1 2 Debugging on Linux for s/390 & z/Architecture 3 by 4 Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com) 5 Copyright (C) 2000-2001 IBM Deutschland Entwicklung GmbH, IBM Corporation 6 Best viewed with fixed width fonts 7 8Overview of Document: 9===================== 10This document is intended to give a good overview of how to debug 11Linux for s/390 & z/Architecture. It isn't intended as a complete reference & not a 12tutorial on the fundamentals of C & assembly. It doesn't go into 13390 IO in any detail. It is intended to complement the documents in the 14reference section below & any other worthwhile references you get. 15 16It is intended like the Enterprise Systems Architecture/390 Reference Summary 17to be printed out & used as a quick cheat sheet self help style reference when 18problems occur. 19 20Contents 21======== 22Register Set 23Address Spaces on Intel Linux 24Address Spaces on Linux for s/390 & z/Architecture 25The Linux for s/390 & z/Architecture Kernel Task Structure 26Register Usage & Stackframes on Linux for s/390 & z/Architecture 27A sample program with comments 28Compiling programs for debugging on Linux for s/390 & z/Architecture 29Figuring out gcc compile errors 30Debugging Tools 31objdump 32strace 33Performance Debugging 34Debugging under VM 35s/390 & z/Architecture IO Overview 36Debugging IO on s/390 & z/Architecture under VM 37GDB on s/390 & z/Architecture 38Stack chaining in gdb by hand 39Examining core dumps 40ldd 41Debugging modules 42The proc file system 43Starting points for debugging scripting languages etc. 44Dumptool & Lcrash 45SysRq 46References 47Special Thanks 48 49Register Set 50============ 51The current architectures have the following registers. 52 5316 General propose registers, 32 bit on s/390 64 bit on z/Architecture, r0-r15 or gpr0-gpr15 used for arithmetic & addressing. 54 5516 Control registers, 32 bit on s/390 64 bit on z/Architecture, ( cr0-cr15 kernel usage only ) used for memory management, 56interrupt control,debugging control etc. 57 5816 Access registers ( ar0-ar15 ) 32 bit on s/390 & z/Architecture 59not used by normal programs but potentially could 60be used as temporary storage. Their main purpose is their 1 to 1 61association with general purpose registers and are used in 62the kernel for copying data between kernel & user address spaces. 63Access register 0 ( & access register 1 on z/Architecture ( needs 64 bit 64pointer ) ) is currently used by the pthread library as a pointer to 65the current running threads private area. 66 6716 64 bit floating point registers (fp0-fp15 ) IEEE & HFP floating 68point format compliant on G5 upwards & a Floating point control reg (FPC) 694 64 bit registers (fp0,fp2,fp4 & fp6) HFP only on older machines. 70Note: 71Linux (currently) always uses IEEE & emulates G5 IEEE format on older machines, 72( provided the kernel is configured for this ). 73 74 75The PSW is the most important register on the machine it 76is 64 bit on s/390 & 128 bit on z/Architecture & serves the roles of 77a program counter (pc), condition code register,memory space designator. 78In IBM standard notation I am counting bit 0 as the MSB. 79It has several advantages over a normal program counter 80in that you can change address translation & program counter 81in a single instruction. To change address translation, 82e.g. switching address translation off requires that you 83have a logical=physical mapping for the address you are 84currently running at. 85 86 Bit Value 87s/390 z/Architecture 880 0 Reserved ( must be 0 ) otherwise specification exception occurs. 89 901 1 Program Event Recording 1 PER enabled, 91 PER is used to facilitate debugging e.g. single stepping. 92 932-4 2-4 Reserved ( must be 0 ). 94 955 5 Dynamic address translation 1=DAT on. 96 976 6 Input/Output interrupt Mask 98 997 7 External interrupt Mask used primarily for interprocessor signalling & 100 clock interrupts. 101 1028-11 8-11 PSW Key used for complex memory protection mechanism not used under linux 103 10412 12 1 on s/390 0 on z/Architecture 105 10613 13 Machine Check Mask 1=enable machine check interrupts 107 10814 14 Wait State set this to 1 to stop the processor except for interrupts & give 109 time to other LPARS used in CPU idle in the kernel to increase overall 110 usage of processor resources. 111 11215 15 Problem state ( if set to 1 certain instructions are disabled ) 113 all linux user programs run with this bit 1 114 ( useful info for debugging under VM ). 115 11616-17 16-17 Address Space Control 117 118 00 Primary Space Mode when DAT on 119 The linux kernel currently runs in this mode, CR1 is affiliated with 120 this mode & points to the primary segment table origin etc. 121 122 01 Access register mode this mode is used in functions to 123 copy data between kernel & user space. 124 125 10 Secondary space mode not used in linux however CR7 the 126 register affiliated with this mode is & this & normally 127 CR13=CR7 to allow us to copy data between kernel & user space. 128 We do this as follows: 129 We set ar2 to 0 to designate its 130 affiliated gpr ( gpr2 )to point to primary=kernel space. 131 We set ar4 to 1 to designate its 132 affiliated gpr ( gpr4 ) to point to secondary=home=user space 133 & then essentially do a memcopy(gpr2,gpr4,size) to 134 copy data between the address spaces, the reason we use home space for the 135 kernel & don't keep secondary space free is that code will not run in 136 secondary space. 137 138 11 Home Space Mode all user programs run in this mode. 139 it is affiliated with CR13. 140 14118-19 18-19 Condition codes (CC) 142 14320 20 Fixed point overflow mask if 1=FPU exceptions for this event 144 occur ( normally 0 ) 145 14621 21 Decimal overflow mask if 1=FPU exceptions for this event occur 147 ( normally 0 ) 148 14922 22 Exponent underflow mask if 1=FPU exceptions for this event occur 150 ( normally 0 ) 151 15223 23 Significance Mask if 1=FPU exceptions for this event occur 153 ( normally 0 ) 154 15524-31 24-30 Reserved Must be 0. 156 157 31 Extended Addressing Mode 158 32 Basic Addressing Mode 159 Used to set addressing mode 160 PSW 31 PSW 32 161 0 0 24 bit 162 0 1 31 bit 163 1 1 64 bit 164 16532 1=31 bit addressing mode 0=24 bit addressing mode (for backward 166 compatibility), linux always runs with this bit set to 1 167 16833-64 Instruction address. 169 33-63 Reserved must be 0 170 64-127 Address 171 In 24 bits mode bits 64-103=0 bits 104-127 Address 172 In 31 bits mode bits 64-96=0 bits 97-127 Address 173 Note: unlike 31 bit mode on s/390 bit 96 must be zero 174 when loading the address with LPSWE otherwise a 175 specification exception occurs, LPSW is fully backward 176 compatible. 177 178 179Prefix Page(s) 180-------------- 181This per cpu memory area is too intimately tied to the processor not to mention. 182It exists between the real addresses 0-4096 on s/390 & 0-8192 z/Architecture & is exchanged 183with a 1 page on s/390 or 2 pages on z/Architecture in absolute storage by the set 184prefix instruction in linux'es startup. 185This page is mapped to a different prefix for each processor in an SMP configuration 186( assuming the os designer is sane of course :-) ). 187Bytes 0-512 ( 200 hex ) on s/390 & 0-512,4096-4544,4604-5119 currently on z/Architecture 188are used by the processor itself for holding such information as exception indications & 189entry points for exceptions. 190Bytes after 0xc00 hex are used by linux for per processor globals on s/390 & z/Architecture 191( there is a gap on z/Architecture too currently between 0xc00 & 1000 which linux uses ). 192The closest thing to this on traditional architectures is the interrupt 193vector table. This is a good thing & does simplify some of the kernel coding 194however it means that we now cannot catch stray NULL pointers in the 195kernel without hard coded checks. 196 197 198 199Address Spaces on Intel Linux 200============================= 201 202The traditional Intel Linux is approximately mapped as follows forgive 203the ascii art. 2040xFFFFFFFF 4GB Himem ***************** 205 * * 206 * Kernel Space * 207 * * 208 ***************** **************** 209User Space Himem (typically 0xC0000000 3GB )* User Stack * * * 210 ***************** * * 211 * Shared Libs * * Next Process * 212 ***************** * to * 213 * * <== * Run * <== 214 * User Program * * * 215 * Data BSS * * * 216 * Text * * * 217 * Sections * * * 2180x00000000 ***************** **************** 219 220Now it is easy to see that on Intel it is quite easy to recognise a kernel address 221as being one greater than user space himem ( in this case 0xC0000000). 222& addresses of less than this are the ones in the current running program on this 223processor ( if an smp box ). 224If using the virtual machine ( VM ) as a debugger it is quite difficult to 225know which user process is running as the address space you are looking at 226could be from any process in the run queue. 227 228The limitation of Intels addressing technique is that the linux 229kernel uses a very simple real address to virtual addressing technique 230of Real Address=Virtual Address-User Space Himem. 231This means that on Intel the kernel linux can typically only address 232Himem=0xFFFFFFFF-0xC0000000=1GB & this is all the RAM these machines 233can typically use. 234They can lower User Himem to 2GB or lower & thus be 235able to use 2GB of RAM however this shrinks the maximum size 236of User Space from 3GB to 2GB they have a no win limit of 4GB unless 237they go to 64 Bit. 238 239 240On 390 our limitations & strengths make us slightly different. 241For backward compatibility we are only allowed use 31 bits (2GB) 242of our 32 bit addresses, however, we use entirely separate address 243spaces for the user & kernel. 244 245This means we can support 2GB of non Extended RAM on s/390, & more 246with the Extended memory management swap device & 247currently 4TB of physical memory currently on z/Architecture. 248 249 250Address Spaces on Linux for s/390 & z/Architecture 251================================================== 252 253Our addressing scheme is as follows 254 255 256Himem 0x7fffffff 2GB on s/390 ***************** **************** 257currently 0x3ffffffffff (2^42)-1 * User Stack * * * 258on z/Architecture. ***************** * * 259 * Shared Libs * * * 260 ***************** * * 261 * * * Kernel * 262 * User Program * * * 263 * Data BSS * * * 264 * Text * * * 265 * Sections * * * 2660x00000000 ***************** **************** 267 268This also means that we need to look at the PSW problem state bit 269or the addressing mode to decide whether we are looking at 270user or kernel space. 271 272Virtual Addresses on s/390 & z/Architecture 273=========================================== 274 275A virtual address on s/390 is made up of 3 parts 276The SX ( segment index, roughly corresponding to the PGD & PMD in linux terminology ) 277being bits 1-11. 278The PX ( page index, corresponding to the page table entry (pte) in linux terminology ) 279being bits 12-19. 280The remaining bits BX (the byte index are the offset in the page ) 281i.e. bits 20 to 31. 282 283On z/Architecture in linux we currently make up an address from 4 parts. 284The region index bits (RX) 0-32 we currently use bits 22-32 285The segment index (SX) being bits 33-43 286The page index (PX) being bits 44-51 287The byte index (BX) being bits 52-63 288 289Notes: 2901) s/390 has no PMD so the PMD is really the PGD also. 291A lot of this stuff is defined in pgtable.h. 292 2932) Also seeing as s/390's page indexes are only 1k in size 294(bits 12-19 x 4 bytes per pte ) we use 1 ( page 4k ) 295to make the best use of memory by updating 4 segment indices 296entries each time we mess with a PMD & use offsets 2970,1024,2048 & 3072 in this page as for our segment indexes. 298On z/Architecture our page indexes are now 2k in size 299( bits 12-19 x 8 bytes per pte ) we do a similar trick 300but only mess with 2 segment indices each time we mess with 301a PMD. 302 3033) As z/Architecture supports up to a massive 5-level page table lookup we 304can only use 3 currently on Linux ( as this is all the generic kernel 305currently supports ) however this may change in future 306this allows us to access ( according to my sums ) 3074TB of virtual storage per process i.e. 3084096*512(PTES)*1024(PMDS)*2048(PGD) = 4398046511104 bytes, 309enough for another 2 or 3 of years I think :-). 310to do this we use a region-third-table designation type in 311our address space control registers. 312 313 314The Linux for s/390 & z/Architecture Kernel Task Structure 315========================================================== 316Each process/thread under Linux for S390 has its own kernel task_struct 317defined in linux/include/linux/sched.h 318The S390 on initialisation & resuming of a process on a cpu sets 319the __LC_KERNEL_STACK variable in the spare prefix area for this cpu 320(which we use for per-processor globals). 321 322The kernel stack pointer is intimately tied with the task structure for 323each processor as follows. 324 325 s/390 326 ************************ 327 * 1 page kernel stack * 328 * ( 4K ) * 329 ************************ 330 * 1 page task_struct * 331 * ( 4K ) * 3328K aligned ************************ 333 334 z/Architecture 335 ************************ 336 * 2 page kernel stack * 337 * ( 8K ) * 338 ************************ 339 * 2 page task_struct * 340 * ( 8K ) * 34116K aligned ************************ 342 343What this means is that we don't need to dedicate any register or global variable 344to point to the current running process & can retrieve it with the following 345very simple construct for s/390 & one very similar for z/Architecture. 346 347static inline struct task_struct * get_current(void) 348{ 349 struct task_struct *current; 350 __asm__("lhi %0,-8192\n\t" 351 "nr %0,15" 352 : "=r" (current) ); 353 return current; 354} 355 356i.e. just anding the current kernel stack pointer with the mask -8192. 357Thankfully because Linux doesn't have support for nested IO interrupts 358& our devices have large buffers can survive interrupts being shut for 359short amounts of time we don't need a separate stack for interrupts. 360 361 362 363 364Register Usage & Stackframes on Linux for s/390 & z/Architecture 365================================================================= 366Overview: 367--------- 368This is the code that gcc produces at the top & the bottom of 369each function. It usually is fairly consistent & similar from 370function to function & if you know its layout you can probably 371make some headway in finding the ultimate cause of a problem 372after a crash without a source level debugger. 373 374Note: To follow stackframes requires a knowledge of C or Pascal & 375limited knowledge of one assembly language. 376 377It should be noted that there are some differences between the 378s/390 & z/Architecture stack layouts as the z/Architecture stack layout didn't have 379to maintain compatibility with older linkage formats. 380 381Glossary: 382--------- 383alloca: 384This is a built in compiler function for runtime allocation 385of extra space on the callers stack which is obviously freed 386up on function exit ( e.g. the caller may choose to allocate nothing 387of a buffer of 4k if required for temporary purposes ), it generates 388very efficient code ( a few cycles ) when compared to alternatives 389like malloc. 390 391automatics: These are local variables on the stack, 392i.e they aren't in registers & they aren't static. 393 394back-chain: 395This is a pointer to the stack pointer before entering a 396framed functions ( see frameless function ) prologue got by 397dereferencing the address of the current stack pointer, 398 i.e. got by accessing the 32 bit value at the stack pointers 399current location. 400 401base-pointer: 402This is a pointer to the back of the literal pool which 403is an area just behind each procedure used to store constants 404in each function. 405 406call-clobbered: The caller probably needs to save these registers if there 407is something of value in them, on the stack or elsewhere before making a 408call to another procedure so that it can restore it later. 409 410epilogue: 411The code generated by the compiler to return to the caller. 412 413frameless-function 414A frameless function in Linux for s390 & z/Architecture is one which doesn't 415need more than the register save area ( 96 bytes on s/390, 160 on z/Architecture ) 416given to it by the caller. 417A frameless function never: 4181) Sets up a back chain. 4192) Calls alloca. 4203) Calls other normal functions 4214) Has automatics. 422 423GOT-pointer: 424This is a pointer to the global-offset-table in ELF 425( Executable Linkable Format, Linux'es most common executable format ), 426all globals & shared library objects are found using this pointer. 427 428lazy-binding 429ELF shared libraries are typically only loaded when routines in the shared 430library are actually first called at runtime. This is lazy binding. 431 432procedure-linkage-table 433This is a table found from the GOT which contains pointers to routines 434in other shared libraries which can't be called to by easier means. 435 436prologue: 437The code generated by the compiler to set up the stack frame. 438 439outgoing-args: 440This is extra area allocated on the stack of the calling function if the 441parameters for the callee's cannot all be put in registers, the same 442area can be reused by each function the caller calls. 443 444routine-descriptor: 445A COFF executable format based concept of a procedure reference 446actually being 8 bytes or more as opposed to a simple pointer to the routine. 447This is typically defined as follows 448Routine Descriptor offset 0=Pointer to Function 449Routine Descriptor offset 4=Pointer to Table of Contents 450The table of contents/TOC is roughly equivalent to a GOT pointer. 451& it means that shared libraries etc. can be shared between several 452environments each with their own TOC. 453 454 455static-chain: This is used in nested functions a concept adopted from pascal 456by gcc not used in ansi C or C++ ( although quite useful ), basically it 457is a pointer used to reference local variables of enclosing functions. 458You might come across this stuff once or twice in your lifetime. 459 460e.g. 461The function below should return 11 though gcc may get upset & toss warnings 462about unused variables. 463int FunctionA(int a) 464{ 465 int b; 466 FunctionC(int c) 467 { 468 b=c+1; 469 } 470 FunctionC(10); 471 return(b); 472} 473 474 475s/390 & z/Architecture Register usage 476===================================== 477r0 used by syscalls/assembly call-clobbered 478r1 used by syscalls/assembly call-clobbered 479r2 argument 0 / return value 0 call-clobbered 480r3 argument 1 / return value 1 (if long long) call-clobbered 481r4 argument 2 call-clobbered 482r5 argument 3 call-clobbered 483r6 argument 4 saved 484r7 pointer-to arguments 5 to ... saved 485r8 this & that saved 486r9 this & that saved 487r10 static-chain ( if nested function ) saved 488r11 frame-pointer ( if function used alloca ) saved 489r12 got-pointer saved 490r13 base-pointer saved 491r14 return-address saved 492r15 stack-pointer saved 493 494f0 argument 0 / return value ( float/double ) call-clobbered 495f2 argument 1 call-clobbered 496f4 z/Architecture argument 2 saved 497f6 z/Architecture argument 3 saved 498The remaining floating points 499f1,f3,f5 f7-f15 are call-clobbered. 500 501Notes: 502------ 5031) The only requirement is that registers which are used 504by the callee are saved, e.g. the compiler is perfectly 505capable of using r11 for purposes other than a frame a 506frame pointer if a frame pointer is not needed. 5072) In functions with variable arguments e.g. printf the calling procedure 508is identical to one without variable arguments & the same number of 509parameters. However, the prologue of this function is somewhat more 510hairy owing to it having to move these parameters to the stack to 511get va_start, va_arg & va_end to work. 5123) Access registers are currently unused by gcc but are used in 513the kernel. Possibilities exist to use them at the moment for 514temporary storage but it isn't recommended. 5154) Only 4 of the floating point registers are used for 516parameter passing as older machines such as G3 only have only 4 517& it keeps the stack frame compatible with other compilers. 518However with IEEE floating point emulation under linux on the 519older machines you are free to use the other 12. 5205) A long long or double parameter cannot be have the 521first 4 bytes in a register & the second four bytes in the 522outgoing args area. It must be purely in the outgoing args 523area if crossing this boundary. 5246) Floating point parameters are mixed with outgoing args 525on the outgoing args area in the order the are passed in as parameters. 5267) Floating point arguments 2 & 3 are saved in the outgoing args area for 527z/Architecture 528 529 530Stack Frame Layout 531------------------ 532s/390 z/Architecture 5330 0 back chain ( a 0 here signifies end of back chain ) 5344 8 eos ( end of stack, not used on Linux for S390 used in other linkage formats ) 5358 16 glue used in other s/390 linkage formats for saved routine descriptors etc. 53612 24 glue used in other s/390 linkage formats for saved routine descriptors etc. 53716 32 scratch area 53820 40 scratch area 53924 48 saved r6 of caller function 54028 56 saved r7 of caller function 54132 64 saved r8 of caller function 54236 72 saved r9 of caller function 54340 80 saved r10 of caller function 54444 88 saved r11 of caller function 54548 96 saved r12 of caller function 54652 104 saved r13 of caller function 54756 112 saved r14 of caller function 54860 120 saved r15 of caller function 54964 128 saved f4 of caller function 55072 132 saved f6 of caller function 55180 undefined 55296 160 outgoing args passed from caller to callee 55396+x 160+x possible stack alignment ( 8 bytes desirable ) 55496+x+y 160+x+y alloca space of caller ( if used ) 55596+x+y+z 160+x+y+z automatics of caller ( if used ) 5560 back-chain 557 558A sample program with comments. 559=============================== 560 561Comments on the function test 562----------------------------- 5631) It didn't need to set up a pointer to the constant pool gpr13 as it isn't used 564( :-( ). 5652) This is a frameless function & no stack is bought. 5663) The compiler was clever enough to recognise that it could return the 567value in r2 as well as use it for the passed in parameter ( :-) ). 5684) The basr ( branch relative & save ) trick works as follows the instruction 569has a special case with r0,r0 with some instruction operands is understood as 570the literal value 0, some risc architectures also do this ). So now 571we are branching to the next address & the address new program counter is 572in r13,so now we subtract the size of the function prologue we have executed 573+ the size of the literal pool to get to the top of the literal pool 5740040037c int test(int b) 575{ # Function prologue below 576 40037c: 90 de f0 34 stm %r13,%r14,52(%r15) # Save registers r13 & r14 577 400380: 0d d0 basr %r13,%r0 # Set up pointer to constant pool using 578 400382: a7 da ff fa ahi %r13,-6 # basr trick 579 return(5+b); 580 # Huge main program 581 400386: a7 2a 00 05 ahi %r2,5 # add 5 to r2 582 583 # Function epilogue below 584 40038a: 98 de f0 34 lm %r13,%r14,52(%r15) # restore registers r13 & 14 585 40038e: 07 fe br %r14 # return 586} 587 588Comments on the function main 589----------------------------- 5901) The compiler did this function optimally ( 8-) ) 591 592Literal pool for main. 593400390: ff ff ff ec .long 0xffffffec 594main(int argc,char *argv[]) 595{ # Function prologue below 596 400394: 90 bf f0 2c stm %r11,%r15,44(%r15) # Save necessary registers 597 400398: 18 0f lr %r0,%r15 # copy stack pointer to r0 598 40039a: a7 fa ff a0 ahi %r15,-96 # Make area for callee saving 599 40039e: 0d d0 basr %r13,%r0 # Set up r13 to point to 600 4003a0: a7 da ff f0 ahi %r13,-16 # literal pool 601 4003a4: 50 00 f0 00 st %r0,0(%r15) # Save backchain 602 603 return(test(5)); # Main Program Below 604 4003a8: 58 e0 d0 00 l %r14,0(%r13) # load relative address of test from 605 # literal pool 606 4003ac: a7 28 00 05 lhi %r2,5 # Set first parameter to 5 607 4003b0: 4d ee d0 00 bas %r14,0(%r14,%r13) # jump to test setting r14 as return 608 # address using branch & save instruction. 609 610 # Function Epilogue below 611 4003b4: 98 bf f0 8c lm %r11,%r15,140(%r15)# Restore necessary registers. 612 4003b8: 07 fe br %r14 # return to do program exit 613} 614 615 616Compiler updates 617---------------- 618 619main(int argc,char *argv[]) 620{ 621 4004fc: 90 7f f0 1c stm %r7,%r15,28(%r15) 622 400500: a7 d5 00 04 bras %r13,400508 <main+0xc> 623 400504: 00 40 04 f4 .long 0x004004f4 624 # compiler now puts constant pool in code to so it saves an instruction 625 400508: 18 0f lr %r0,%r15 626 40050a: a7 fa ff a0 ahi %r15,-96 627 40050e: 50 00 f0 00 st %r0,0(%r15) 628 return(test(5)); 629 400512: 58 10 d0 00 l %r1,0(%r13) 630 400516: a7 28 00 05 lhi %r2,5 631 40051a: 0d e1 basr %r14,%r1 632 # compiler adds 1 extra instruction to epilogue this is done to 633 # avoid processor pipeline stalls owing to data dependencies on g5 & 634 # above as register 14 in the old code was needed directly after being loaded 635 # by the lm %r11,%r15,140(%r15) for the br %14. 636 40051c: 58 40 f0 98 l %r4,152(%r15) 637 400520: 98 7f f0 7c lm %r7,%r15,124(%r15) 638 400524: 07 f4 br %r4 639} 640 641 642Hartmut ( our compiler developer ) also has been threatening to take out the 643stack backchain in optimised code as this also causes pipeline stalls, you 644have been warned. 645 64664 bit z/Architecture code disassembly 647-------------------------------------- 648 649If you understand the stuff above you'll understand the stuff 650below too so I'll avoid repeating myself & just say that 651some of the instructions have g's on the end of them to indicate 652they are 64 bit & the stack offsets are a bigger, 653the only other difference you'll find between 32 & 64 bit is that 654we now use f4 & f6 for floating point arguments on 64 bit. 65500000000800005b0 <test>: 656int test(int b) 657{ 658 return(5+b); 659 800005b0: a7 2a 00 05 ahi %r2,5 660 800005b4: b9 14 00 22 lgfr %r2,%r2 # downcast to integer 661 800005b8: 07 fe br %r14 662 800005ba: 07 07 bcr 0,%r7 663 664 665} 666 66700000000800005bc <main>: 668main(int argc,char *argv[]) 669{ 670 800005bc: eb bf f0 58 00 24 stmg %r11,%r15,88(%r15) 671 800005c2: b9 04 00 1f lgr %r1,%r15 672 800005c6: a7 fb ff 60 aghi %r15,-160 673 800005ca: e3 10 f0 00 00 24 stg %r1,0(%r15) 674 return(test(5)); 675 800005d0: a7 29 00 05 lghi %r2,5 676 # brasl allows jumps > 64k & is overkill here bras would do fune 677 800005d4: c0 e5 ff ff ff ee brasl %r14,800005b0 <test> 678 800005da: e3 40 f1 10 00 04 lg %r4,272(%r15) 679 800005e0: eb bf f0 f8 00 04 lmg %r11,%r15,248(%r15) 680 800005e6: 07 f4 br %r4 681} 682 683 684 685Compiling programs for debugging on Linux for s/390 & z/Architecture 686==================================================================== 687-gdwarf-2 now works it should be considered the default debugging 688format for s/390 & z/Architecture as it is more reliable for debugging 689shared libraries, normal -g debugging works much better now 690Thanks to the IBM java compiler developers bug reports. 691 692This is typically done adding/appending the flags -g or -gdwarf-2 to the 693CFLAGS & LDFLAGS variables Makefile of the program concerned. 694 695If using gdb & you would like accurate displays of registers & 696 stack traces compile without optimisation i.e make sure 697that there is no -O2 or similar on the CFLAGS line of the Makefile & 698the emitted gcc commands, obviously this will produce worse code 699( not advisable for shipment ) but it is an aid to the debugging process. 700 701This aids debugging because the compiler will copy parameters passed in 702in registers onto the stack so backtracing & looking at passed in 703parameters will work, however some larger programs which use inline functions 704will not compile without optimisation. 705 706Debugging with optimisation has since much improved after fixing 707some bugs, please make sure you are using gdb-5.0 or later developed 708after Nov'2000. 709 710Figuring out gcc compile errors 711=============================== 712If you are getting a lot of syntax errors compiling a program & the problem 713isn't blatantly obvious from the source. 714It often helps to just preprocess the file, this is done with the -E 715option in gcc. 716What this does is that it runs through the very first phase of compilation 717( compilation in gcc is done in several stages & gcc calls many programs to 718achieve its end result ) with the -E option gcc just calls the gcc preprocessor (cpp). 719The c preprocessor does the following, it joins all the files #included together 720recursively ( #include files can #include other files ) & also the c file you wish to compile. 721It puts a fully qualified path of the #included files in a comment & it 722does macro expansion. 723This is useful for debugging because 7241) You can double check whether the files you expect to be included are the ones 725that are being included ( e.g. double check that you aren't going to the i386 asm directory ). 7262) Check that macro definitions aren't clashing with typedefs, 7273) Check that definitions aren't being used before they are being included. 7284) Helps put the line emitting the error under the microscope if it contains macros. 729 730For convenience the Linux kernel's makefile will do preprocessing automatically for you 731by suffixing the file you want built with .i ( instead of .o ) 732 733e.g. 734from the linux directory type 735make arch/s390/kernel/signal.i 736this will build 737 738s390-gcc -D__KERNEL__ -I/home1/barrow/linux/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer 739-fno-strict-aliasing -D__SMP__ -pipe -fno-strength-reduce -E arch/s390/kernel/signal.c 740> arch/s390/kernel/signal.i 741 742Now look at signal.i you should see something like. 743 744 745# 1 "/home1/barrow/linux/include/asm/types.h" 1 746typedef unsigned short umode_t; 747typedef __signed__ char __s8; 748typedef unsigned char __u8; 749typedef __signed__ short __s16; 750typedef unsigned short __u16; 751 752If instead you are getting errors further down e.g. 753unknown instruction:2515 "move.l" or better still unknown instruction:2515 754"Fixme not implemented yet, call Martin" you are probably are attempting to compile some code 755meant for another architecture or code that is simply not implemented, with a fixme statement 756stuck into the inline assembly code so that the author of the file now knows he has work to do. 757To look at the assembly emitted by gcc just before it is about to call gas ( the gnu assembler ) 758use the -S option. 759Again for your convenience the Linux kernel's Makefile will hold your hand & 760do all this donkey work for you also by building the file with the .s suffix. 761e.g. 762from the Linux directory type 763make arch/s390/kernel/signal.s 764 765s390-gcc -D__KERNEL__ -I/home1/barrow/linux/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer 766-fno-strict-aliasing -D__SMP__ -pipe -fno-strength-reduce -S arch/s390/kernel/signal.c 767-o arch/s390/kernel/signal.s 768 769 770This will output something like, ( please note the constant pool & the useful comments 771in the prologue to give you a hand at interpreting it ). 772 773.LC54: 774 .string "misaligned (__u16 *) in __xchg\n" 775.LC57: 776 .string "misaligned (__u32 *) in __xchg\n" 777.L$PG1: # Pool sys_sigsuspend 778.LC192: 779 .long -262401 780.LC193: 781 .long -1 782.LC194: 783 .long schedule-.L$PG1 784.LC195: 785 .long do_signal-.L$PG1 786 .align 4 787.globl sys_sigsuspend 788 .type sys_sigsuspend,@function 789sys_sigsuspend: 790# leaf function 0 791# automatics 16 792# outgoing args 0 793# need frame pointer 0 794# call alloca 0 795# has varargs 0 796# incoming args (stack) 0 797# function length 168 798 STM 8,15,32(15) 799 LR 0,15 800 AHI 15,-112 801 BASR 13,0 802.L$CO1: AHI 13,.L$PG1-.L$CO1 803 ST 0,0(15) 804 LR 8,2 805 N 5,.LC192-.L$PG1(13) 806 807Adding -g to the above output makes the output even more useful 808e.g. typing 809make CC:="s390-gcc -g" kernel/sched.s 810 811which compiles. 812s390-gcc -g -D__KERNEL__ -I/home/barrow/linux-2.3/include -Wall -Wstrict-prototypes -O2 -fomit-frame-pointer -fno-strict-aliasing -pipe -fno-strength-reduce -S kernel/sched.c -o kernel/sched.s 813 814also outputs stabs ( debugger ) info, from this info you can find out the 815offsets & sizes of various elements in structures. 816e.g. the stab for the structure 817struct rlimit { 818 unsigned long rlim_cur; 819 unsigned long rlim_max; 820}; 821is 822.stabs "rlimit:T(151,2)=s8rlim_cur:(0,5),0,32;rlim_max:(0,5),32,32;;",128,0,0,0 823from this stab you can see that 824rlimit_cur starts at bit offset 0 & is 32 bits in size 825rlimit_max starts at bit offset 32 & is 32 bits in size. 826 827 828Debugging Tools: 829================ 830 831objdump 832======= 833This is a tool with many options the most useful being ( if compiled with -g). 834objdump --source <victim program or object file> > <victims debug listing > 835 836 837The whole kernel can be compiled like this ( Doing this will make a 17MB kernel 838& a 200 MB listing ) however you have to strip it before building the image 839using the strip command to make it a more reasonable size to boot it. 840 841A source/assembly mixed dump of the kernel can be done with the line 842objdump --source vmlinux > vmlinux.lst 843Also, if the file isn't compiled -g, this will output as much debugging information 844as it can (e.g. function names). This is very slow as it spends lots 845of time searching for debugging info. The following self explanatory line should be used 846instead if the code isn't compiled -g, as it is much faster: 847objdump --disassemble-all --syms vmlinux > vmlinux.lst 848 849As hard drive space is valuable most of us use the following approach. 8501) Look at the emitted psw on the console to find the crash address in the kernel. 8512) Look at the file System.map ( in the linux directory ) produced when building 852the kernel to find the closest address less than the current PSW to find the 853offending function. 8543) use grep or similar to search the source tree looking for the source file 855 with this function if you don't know where it is. 8564) rebuild this object file with -g on, as an example suppose the file was 857( /arch/s390/kernel/signal.o ) 8585) Assuming the file with the erroneous function is signal.c Move to the base of the 859Linux source tree. 8606) rm /arch/s390/kernel/signal.o 8617) make /arch/s390/kernel/signal.o 8628) watch the gcc command line emitted 8639) type it in again or alternatively cut & paste it on the console adding the -g option. 86410) objdump --source arch/s390/kernel/signal.o > signal.lst 865This will output the source & the assembly intermixed, as the snippet below shows 866This will unfortunately output addresses which aren't the same 867as the kernel ones you should be able to get around the mental arithmetic 868by playing with the --adjust-vma parameter to objdump. 869 870 871 872 873static inline void spin_lock(spinlock_t *lp) 874{ 875 a0: 18 34 lr %r3,%r4 876 a2: a7 3a 03 bc ahi %r3,956 877 __asm__ __volatile(" lhi 1,-1\n" 878 a6: a7 18 ff ff lhi %r1,-1 879 aa: 1f 00 slr %r0,%r0 880 ac: ba 01 30 00 cs %r0,%r1,0(%r3) 881 b0: a7 44 ff fd jm aa <sys_sigsuspend+0x2e> 882 saveset = current->blocked; 883 b4: d2 07 f0 68 mvc 104(8,%r15),972(%r4) 884 b8: 43 cc 885 return (set->sig[0] & mask) != 0; 886} 887 8886) If debugging under VM go down to that section in the document for more info. 889 890 891I now have a tool which takes the pain out of --adjust-vma 892& you are able to do something like 893make /arch/s390/kernel/traps.lst 894& it automatically generates the correctly relocated entries for 895the text segment in traps.lst. 896This tool is now standard in linux distro's in scripts/makelst 897 898strace: 899------- 900Q. What is it ? 901A. It is a tool for intercepting calls to the kernel & logging them 902to a file & on the screen. 903 904Q. What use is it ? 905A. You can use it to find out what files a particular program opens. 906 907 908 909Example 1 910--------- 911If you wanted to know does ping work but didn't have the source 912strace ping -c 1 127.0.0.1 913& then look at the man pages for each of the syscalls below, 914( In fact this is sometimes easier than looking at some spaghetti 915source which conditionally compiles for several architectures ). 916Not everything that it throws out needs to make sense immediately. 917 918Just looking quickly you can see that it is making up a RAW socket 919for the ICMP protocol. 920Doing an alarm(10) for a 10 second timeout 921& doing a gettimeofday call before & after each read to see 922how long the replies took, & writing some text to stdout so the user 923has an idea what is going on. 924 925socket(PF_INET, SOCK_RAW, IPPROTO_ICMP) = 3 926getuid() = 0 927setuid(0) = 0 928stat("/usr/share/locale/C/libc.cat", 0xbffff134) = -1 ENOENT (No such file or directory) 929stat("/usr/share/locale/libc/C", 0xbffff134) = -1 ENOENT (No such file or directory) 930stat("/usr/local/share/locale/C/libc.cat", 0xbffff134) = -1 ENOENT (No such file or directory) 931getpid() = 353 932setsockopt(3, SOL_SOCKET, SO_BROADCAST, [1], 4) = 0 933setsockopt(3, SOL_SOCKET, SO_RCVBUF, [49152], 4) = 0 934fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(3, 1), ...}) = 0 935mmap(0, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40008000 936ioctl(1, TCGETS, {B9600 opost isig icanon echo ...}) = 0 937write(1, "PING 127.0.0.1 (127.0.0.1): 56 d"..., 42PING 127.0.0.1 (127.0.0.1): 56 data bytes 938) = 42 939sigaction(SIGINT, {0x8049ba0, [], SA_RESTART}, {SIG_DFL}) = 0 940sigaction(SIGALRM, {0x8049600, [], SA_RESTART}, {SIG_DFL}) = 0 941gettimeofday({948904719, 138951}, NULL) = 0 942sendto(3, "\10\0D\201a\1\0\0\17#\2178\307\36"..., 64, 0, {sin_family=AF_INET, 943sin_port=htons(0), sin_addr=inet_addr("127.0.0.1")}, 16) = 64 944sigaction(SIGALRM, {0x8049600, [], SA_RESTART}, {0x8049600, [], SA_RESTART}) = 0 945sigaction(SIGALRM, {0x8049ba0, [], SA_RESTART}, {0x8049600, [], SA_RESTART}) = 0 946alarm(10) = 0 947recvfrom(3, "E\0\0T\0005\0\0@\1|r\177\0\0\1\177"..., 192, 0, 948{sin_family=AF_INET, sin_port=htons(50882), sin_addr=inet_addr("127.0.0.1")}, [16]) = 84 949gettimeofday({948904719, 160224}, NULL) = 0 950recvfrom(3, "E\0\0T\0006\0\0\377\1\275p\177\0"..., 192, 0, 951{sin_family=AF_INET, sin_port=htons(50882), sin_addr=inet_addr("127.0.0.1")}, [16]) = 84 952gettimeofday({948904719, 166952}, NULL) = 0 953write(1, "64 bytes from 127.0.0.1: icmp_se"..., 9545764 bytes from 127.0.0.1: icmp_seq=0 ttl=255 time=28.0 ms 955 956Example 2 957--------- 958strace passwd 2>&1 | grep open 959produces the following output 960open("/etc/ld.so.cache", O_RDONLY) = 3 961open("/opt/kde/lib/libc.so.5", O_RDONLY) = -1 ENOENT (No such file or directory) 962open("/lib/libc.so.5", O_RDONLY) = 3 963open("/dev", O_RDONLY) = 3 964open("/var/run/utmp", O_RDONLY) = 3 965open("/etc/passwd", O_RDONLY) = 3 966open("/etc/shadow", O_RDONLY) = 3 967open("/etc/login.defs", O_RDONLY) = 4 968open("/dev/tty", O_RDONLY) = 4 969 970The 2>&1 is done to redirect stderr to stdout & grep is then filtering this input 971through the pipe for each line containing the string open. 972 973 974Example 3 975--------- 976Getting sophisticated 977telnetd crashes & I don't know why 978 979Steps 980----- 9811) Replace the following line in /etc/inetd.conf 982telnet stream tcp nowait root /usr/sbin/in.telnetd -h 983with 984telnet stream tcp nowait root /blah 985 9862) Create the file /blah with the following contents to start tracing telnetd 987#!/bin/bash 988/usr/bin/strace -o/t1 -f /usr/sbin/in.telnetd -h 9893) chmod 700 /blah to make it executable only to root 9904) 991killall -HUP inetd 992or ps aux | grep inetd 993get inetd's process id 994& kill -HUP inetd to restart it. 995 996Important options 997----------------- 998-o is used to tell strace to output to a file in our case t1 in the root directory 999-f is to follow children i.e. 1000e.g in our case above telnetd will start the login process & subsequently a shell like bash. 1001You will be able to tell which is which from the process ID's listed on the left hand side 1002of the strace output. 1003-p<pid> will tell strace to attach to a running process, yup this can be done provided 1004 it isn't being traced or debugged already & you have enough privileges, 1005the reason 2 processes cannot trace or debug the same program is that strace 1006becomes the parent process of the one being debugged & processes ( unlike people ) 1007can have only one parent. 1008 1009 1010However the file /t1 will get big quite quickly 1011to test it telnet 127.0.0.1 1012 1013now look at what files in.telnetd execve'd 1014413 execve("/usr/sbin/in.telnetd", ["/usr/sbin/in.telnetd", "-h"], [/* 17 vars */]) = 0 1015414 execve("/bin/login", ["/bin/login", "-h", "localhost", "-p"], [/* 2 vars */]) = 0 1016 1017Whey it worked!. 1018 1019 1020Other hints: 1021------------ 1022If the program is not very interactive ( i.e. not much keyboard input ) 1023& is crashing in one architecture but not in another you can do 1024an strace of both programs under as identical a scenario as you can 1025on both architectures outputting to a file then. 1026do a diff of the two traces using the diff program 1027i.e. 1028diff output1 output2 1029& maybe you'll be able to see where the call paths differed, this 1030is possibly near the cause of the crash. 1031 1032More info 1033--------- 1034Look at man pages for strace & the various syscalls 1035e.g. man strace, man alarm, man socket. 1036 1037 1038Performance Debugging 1039===================== 1040gcc is capable of compiling in profiling code just add the -p option 1041to the CFLAGS, this obviously affects program size & performance. 1042This can be used by the gprof gnu profiling tool or the 1043gcov the gnu code coverage tool ( code coverage is a means of testing 1044code quality by checking if all the code in an executable in exercised by 1045a tester ). 1046 1047 1048Using top to find out where processes are sleeping in the kernel 1049---------------------------------------------------------------- 1050To do this copy the System.map from the root directory where 1051the linux kernel was built to the /boot directory on your 1052linux machine. 1053Start top 1054Now type fU<return> 1055You should see a new field called WCHAN which 1056tells you where each process is sleeping here is a typical output. 1057 1058 6:59pm up 41 min, 1 user, load average: 0.00, 0.00, 0.00 105928 processes: 27 sleeping, 1 running, 0 zombie, 0 stopped 1060CPU states: 0.0% user, 0.1% system, 0.0% nice, 99.8% idle 1061Mem: 254900K av, 45976K used, 208924K free, 0K shrd, 28636K buff 1062Swap: 0K av, 0K used, 0K free 8620K cached 1063 1064 PID USER PRI NI SIZE RSS SHARE WCHAN STAT LIB %CPU %MEM TIME COMMAND 1065 750 root 12 0 848 848 700 do_select S 0 0.1 0.3 0:00 in.telnetd 1066 767 root 16 0 1140 1140 964 R 0 0.1 0.4 0:00 top 1067 1 root 8 0 212 212 180 do_select S 0 0.0 0.0 0:00 init 1068 2 root 9 0 0 0 0 down_inte SW 0 0.0 0.0 0:00 kmcheck 1069 1070The time command 1071---------------- 1072Another related command is the time command which gives you an indication 1073of where a process is spending the majority of its time. 1074e.g. 1075time ping -c 5 nc 1076outputs 1077real 0m4.054s 1078user 0m0.010s 1079sys 0m0.010s 1080 1081Debugging under VM 1082================== 1083 1084Notes 1085----- 1086Addresses & values in the VM debugger are always hex never decimal 1087Address ranges are of the format <HexValue1>-<HexValue2> or <HexValue1>.<HexValue2> 1088e.g. The address range 0x2000 to 0x3000 can be described as 2000-3000 or 2000.1000 1089 1090The VM Debugger is case insensitive. 1091 1092VM's strengths are usually other debuggers weaknesses you can get at any resource 1093no matter how sensitive e.g. memory management resources,change address translation 1094in the PSW. For kernel hacking you will reap dividends if you get good at it. 1095 1096The VM Debugger displays operators but not operands, probably because some 1097of it was written when memory was expensive & the programmer was probably proud that 1098it fitted into 2k of memory & the programmers & didn't want to shock hardcore VM'ers by 1099changing the interface :-), also the debugger displays useful information on the same line & 1100the author of the code probably felt that it was a good idea not to go over 1101the 80 columns on the screen. 1102 1103As some of you are probably in a panic now this isn't as unintuitive as it may seem 1104as the 390 instructions are easy to decode mentally & you can make a good guess at a lot 1105of them as all the operands are nibble ( half byte aligned ) & if you have an objdump listing 1106also it is quite easy to follow, if you don't have an objdump listing keep a copy of 1107the s/390 Reference Summary & look at between pages 2 & 7 or alternatively the 1108s/390 principles of operation. 1109e.g. even I can guess that 11100001AFF8' LR 180F CC 0 1111is a ( load register ) lr r0,r15 1112 1113Also it is very easy to tell the length of a 390 instruction from the 2 most significant 1114bits in the instruction ( not that this info is really useful except if you are trying to 1115make sense of a hexdump of code ). 1116Here is a table 1117Bits Instruction Length 1118------------------------------------------ 111900 2 Bytes 112001 4 Bytes 112110 4 Bytes 112211 6 Bytes 1123 1124 1125 1126 1127The debugger also displays other useful info on the same line such as the 1128addresses being operated on destination addresses of branches & condition codes. 1129e.g. 113000019736' AHI A7DAFF0E CC 1 1131000198BA' BRC A7840004 -> 000198C2' CC 0 1132000198CE' STM 900EF068 >> 0FA95E78 CC 2 1133 1134 1135 1136Useful VM debugger commands 1137--------------------------- 1138 1139I suppose I'd better mention this before I start 1140to list the current active traces do 1141Q TR 1142there can be a maximum of 255 of these per set 1143( more about trace sets later ). 1144To stop traces issue a 1145TR END. 1146To delete a particular breakpoint issue 1147TR DEL <breakpoint number> 1148 1149The PA1 key drops to CP mode so you can issue debugger commands, 1150Doing alt c (on my 3270 console at least ) clears the screen. 1151hitting b <enter> comes back to the running operating system 1152from cp mode ( in our case linux ). 1153It is typically useful to add shortcuts to your profile.exec file 1154if you have one ( this is roughly equivalent to autoexec.bat in DOS ). 1155file here are a few from mine. 1156/* this gives me command history on issuing f12 */ 1157set pf12 retrieve 1158/* this continues */ 1159set pf8 imm b 1160/* goes to trace set a */ 1161set pf1 imm tr goto a 1162/* goes to trace set b */ 1163set pf2 imm tr goto b 1164/* goes to trace set c */ 1165set pf3 imm tr goto c 1166 1167 1168 1169Instruction Tracing 1170------------------- 1171Setting a simple breakpoint 1172TR I PSWA <address> 1173To debug a particular function try 1174TR I R <function address range> 1175TR I on its own will single step. 1176TR I DATA <MNEMONIC> <OPTIONAL RANGE> will trace for particular mnemonics 1177e.g. 1178TR I DATA 4D R 0197BC.4000 1179will trace for BAS'es ( opcode 4D ) in the range 0197BC.4000 1180if you were inclined you could add traces for all branch instructions & 1181suffix them with the run prefix so you would have a backtrace on screen 1182when a program crashes. 1183TR BR <INTO OR FROM> will trace branches into or out of an address. 1184e.g. 1185TR BR INTO 0 is often quite useful if a program is getting awkward & deciding 1186to branch to 0 & crashing as this will stop at the address before in jumps to 0. 1187TR I R <address range> RUN cmd d g 1188single steps a range of addresses but stays running & 1189displays the gprs on each step. 1190 1191 1192 1193Displaying & modifying Registers 1194-------------------------------- 1195D G will display all the gprs 1196Adding a extra G to all the commands is necessary to access the full 64 bit 1197content in VM on z/Architecture obviously this isn't required for access registers 1198as these are still 32 bit. 1199e.g. DGG instead of DG 1200D X will display all the control registers 1201D AR will display all the access registers 1202D AR4-7 will display access registers 4 to 7 1203CPU ALL D G will display the GRPS of all CPUS in the configuration 1204D PSW will display the current PSW 1205st PSW 2000 will put the value 2000 into the PSW & 1206cause crash your machine. 1207D PREFIX displays the prefix offset 1208 1209 1210Displaying Memory 1211----------------- 1212To display memory mapped using the current PSW's mapping try 1213D <range> 1214To make VM display a message each time it hits a particular address & continue try 1215D I<range> will disassemble/display a range of instructions. 1216ST addr 32 bit word will store a 32 bit aligned address 1217D T<range> will display the EBCDIC in an address ( if you are that way inclined ) 1218D R<range> will display real addresses ( without DAT ) but with prefixing. 1219There are other complex options to display if you need to get at say home space 1220but are in primary space the easiest thing to do is to temporarily 1221modify the PSW to the other addressing mode, display the stuff & then 1222restore it. 1223 1224 1225 1226Hints 1227----- 1228If you want to issue a debugger command without halting your virtual machine with the 1229PA1 key try prefixing the command with #CP e.g. 1230#cp tr i pswa 2000 1231also suffixing most debugger commands with RUN will cause them not 1232to stop just display the mnemonic at the current instruction on the console. 1233If you have several breakpoints you want to put into your program & 1234you get fed up of cross referencing with System.map 1235you can do the following trick for several symbols. 1236grep do_signal System.map 1237which emits the following among other things 12380001f4e0 T do_signal 1239now you can do 1240 1241TR I PSWA 0001f4e0 cmd msg * do_signal 1242This sends a message to your own console each time do_signal is entered. 1243( As an aside I wrote a perl script once which automatically generated a REXX 1244script with breakpoints on every kernel procedure, this isn't a good idea 1245because there are thousands of these routines & VM can only set 255 breakpoints 1246at a time so you nearly had to spend as long pruning the file down as you would 1247entering the msg's by hand ),however, the trick might be useful for a single object file. 1248On linux'es 3270 emulator x3270 there is a very useful option under the file ment 1249Save Screens In File this is very good of keeping a copy of traces. 1250 1251From CMS help <command name> will give you online help on a particular command. 1252e.g. 1253HELP DISPLAY 1254 1255Also CP has a file called profile.exec which automatically gets called 1256on startup of CMS ( like autoexec.bat ), keeping on a DOS analogy session 1257CP has a feature similar to doskey, it may be useful for you to 1258use profile.exec to define some keystrokes. 1259e.g. 1260SET PF9 IMM B 1261This does a single step in VM on pressing F8. 1262SET PF10 ^ 1263This sets up the ^ key. 1264which can be used for ^c (ctrl-c),^z (ctrl-z) which can't be typed directly into some 3270 consoles. 1265SET PF11 ^- 1266This types the starting keystrokes for a sysrq see SysRq below. 1267SET PF12 RETRIEVE 1268This retrieves command history on pressing F12. 1269 1270 1271Sometimes in VM the display is set up to scroll automatically this 1272can be very annoying if there are messages you wish to look at 1273to stop this do 1274TERM MORE 255 255 1275This will nearly stop automatic screen updates, however it will 1276cause a denial of service if lots of messages go to the 3270 console, 1277so it would be foolish to use this as the default on a production machine. 1278 1279 1280Tracing particular processes 1281---------------------------- 1282The kernel's text segment is intentionally at an address in memory that it will 1283very seldom collide with text segments of user programs ( thanks Martin ), 1284this simplifies debugging the kernel. 1285However it is quite common for user processes to have addresses which collide 1286this can make debugging a particular process under VM painful under normal 1287circumstances as the process may change when doing a 1288TR I R <address range>. 1289Thankfully after reading VM's online help I figured out how to debug 1290I particular process. 1291 1292Your first problem is to find the STD ( segment table designation ) 1293of the program you wish to debug. 1294There are several ways you can do this here are a few 12951) objdump --syms <program to be debugged> | grep main 1296To get the address of main in the program. 1297tr i pswa <address of main> 1298Start the program, if VM drops to CP on what looks like the entry 1299point of the main function this is most likely the process you wish to debug. 1300Now do a D X13 or D XG13 on z/Architecture. 1301On 31 bit the STD is bits 1-19 ( the STO segment table origin ) 1302& 25-31 ( the STL segment table length ) of CR13. 1303now type 1304TR I R STD <CR13's value> 0.7fffffff 1305e.g. 1306TR I R STD 8F32E1FF 0.7fffffff 1307Another very useful variation is 1308TR STORE INTO STD <CR13's value> <address range> 1309for finding out when a particular variable changes. 1310 1311An alternative way of finding the STD of a currently running process 1312is to do the following, ( this method is more complex but 1313could be quite convenient if you aren't updating the kernel much & 1314so your kernel structures will stay constant for a reasonable period of 1315time ). 1316 1317grep task /proc/<pid>/status 1318from this you should see something like 1319task: 0f160000 ksp: 0f161de8 pt_regs: 0f161f68 1320This now gives you a pointer to the task structure. 1321Now make CC:="s390-gcc -g" kernel/sched.s 1322To get the task_struct stabinfo. 1323( task_struct is defined in include/linux/sched.h ). 1324Now we want to look at 1325task->active_mm->pgd 1326on my machine the active_mm in the task structure stab is 1327active_mm:(4,12),672,32 1328its offset is 672/8=84=0x54 1329the pgd member in the mm_struct stab is 1330pgd:(4,6)=*(29,5),96,32 1331so its offset is 96/8=12=0xc 1332 1333so we'll 1334hexdump -s 0xf160054 /dev/mem | more 1335i.e. task_struct+active_mm offset 1336to look at the active_mm member 1337f160054 0fee cc60 0019 e334 0000 0000 0000 0011 1338hexdump -s 0x0feecc6c /dev/mem | more 1339i.e. active_mm+pgd offset 1340feecc6c 0f2c 0000 0000 0001 0000 0001 0000 0010 1341we get something like 1342now do 1343TR I R STD <pgd|0x7f> 0.7fffffff 1344i.e. the 0x7f is added because the pgd only 1345gives the page table origin & we need to set the low bits 1346to the maximum possible segment table length. 1347TR I R STD 0f2c007f 0.7fffffff 1348on z/Architecture you'll probably need to do 1349TR I R STD <pgd|0x7> 0.ffffffffffffffff 1350to set the TableType to 0x1 & the Table length to 3. 1351 1352 1353 1354Tracing Program Exceptions 1355-------------------------- 1356If you get a crash which says something like 1357illegal operation or specification exception followed by a register dump 1358You can restart linux & trace these using the tr prog <range or value> trace option. 1359 1360 1361 1362The most common ones you will normally be tracing for is 13631=operation exception 13642=privileged operation exception 13654=protection exception 13665=addressing exception 13676=specification exception 136810=segment translation exception 136911=page translation exception 1370 1371The full list of these is on page 22 of the current s/390 Reference Summary. 1372e.g. 1373tr prog 10 will trace segment translation exceptions. 1374tr prog on its own will trace all program interruption codes. 1375 1376Trace Sets 1377---------- 1378On starting VM you are initially in the INITIAL trace set. 1379You can do a Q TR to verify this. 1380If you have a complex tracing situation where you wish to wait for instance 1381till a driver is open before you start tracing IO, but know in your 1382heart that you are going to have to make several runs through the code till you 1383have a clue whats going on. 1384 1385What you can do is 1386TR I PSWA <Driver open address> 1387hit b to continue till breakpoint 1388reach the breakpoint 1389now do your 1390TR GOTO B 1391TR IO 7c08-7c09 inst int run 1392or whatever the IO channels you wish to trace are & hit b 1393 1394To got back to the initial trace set do 1395TR GOTO INITIAL 1396& the TR I PSWA <Driver open address> will be the only active breakpoint again. 1397 1398 1399Tracing linux syscalls under VM 1400------------------------------- 1401Syscalls are implemented on Linux for S390 by the Supervisor call instruction (SVC) there 256 1402possibilities of these as the instruction is made up of a 0xA opcode & the second byte being 1403the syscall number. They are traced using the simple command. 1404TR SVC <Optional value or range> 1405the syscalls are defined in linux/include/asm-s390/unistd.h 1406e.g. to trace all file opens just do 1407TR SVC 5 ( as this is the syscall number of open ) 1408 1409 1410SMP Specific commands 1411--------------------- 1412To find out how many cpus you have 1413Q CPUS displays all the CPU's available to your virtual machine 1414To find the cpu that the current cpu VM debugger commands are being directed at do 1415Q CPU to change the current cpu VM debugger commands are being directed at do 1416CPU <desired cpu no> 1417 1418On a SMP guest issue a command to all CPUs try prefixing the command with cpu all. 1419To issue a command to a particular cpu try cpu <cpu number> e.g. 1420CPU 01 TR I R 2000.3000 1421If you are running on a guest with several cpus & you have a IO related problem 1422& cannot follow the flow of code but you know it isn't smp related. 1423from the bash prompt issue 1424shutdown -h now or halt. 1425do a Q CPUS to find out how many cpus you have 1426detach each one of them from cp except cpu 0 1427by issuing a 1428DETACH CPU 01-(number of cpus in configuration) 1429& boot linux again. 1430TR SIGP will trace inter processor signal processor instructions. 1431DEFINE CPU 01-(number in configuration) 1432will get your guests cpus back. 1433 1434 1435Help for displaying ascii textstrings 1436------------------------------------- 1437On the very latest VM Nucleus'es VM can now display ascii 1438( thanks Neale for the hint ) by doing 1439D TX<lowaddr>.<len> 1440e.g. 1441D TX0.100 1442 1443Alternatively 1444============= 1445Under older VM debuggers ( I love EBDIC too ) you can use this little program I wrote which 1446will convert a command line of hex digits to ascii text which can be compiled under linux & 1447you can copy the hex digits from your x3270 terminal to your xterm if you are debugging 1448from a linuxbox. 1449 1450This is quite useful when looking at a parameter passed in as a text string 1451under VM ( unless you are good at decoding ASCII in your head ). 1452 1453e.g. consider tracing an open syscall 1454TR SVC 5 1455We have stopped at a breakpoint 1456000151B0' SVC 0A05 -> 0001909A' CC 0 1457 1458D 20.8 to check the SVC old psw in the prefix area & see was it from userspace 1459( for the layout of the prefix area consult P18 of the s/390 390 Reference Summary 1460if you have it available ). 1461V00000020 070C2000 800151B2 1462The problem state bit wasn't set & it's also too early in the boot sequence 1463for it to be a userspace SVC if it was we would have to temporarily switch the 1464psw to user space addressing so we could get at the first parameter of the open in 1465gpr2. 1466Next do a 1467D G2 1468GPR 2 = 00014CB4 1469Now display what gpr2 is pointing to 1470D 00014CB4.20 1471V00014CB4 2F646576 2F636F6E 736F6C65 00001BF5 1472V00014CC4 FC00014C B4001001 E0001000 B8070707 1473Now copy the text till the first 00 hex ( which is the end of the string 1474to an xterm & do hex2ascii on it. 1475hex2ascii 2F646576 2F636F6E 736F6C65 00 1476outputs 1477Decoded Hex:=/ d e v / c o n s o l e 0x00 1478We were opening the console device, 1479 1480You can compile the code below yourself for practice :-), 1481/* 1482 * hex2ascii.c 1483 * a useful little tool for converting a hexadecimal command line to ascii 1484 * 1485 * Author(s): Denis Joseph Barrow (djbarrow@de.ibm.com,barrow_dj@yahoo.com) 1486 * (C) 2000 IBM Deutschland Entwicklung GmbH, IBM Corporation. 1487 */ 1488#include <stdio.h> 1489 1490int main(int argc,char *argv[]) 1491{ 1492 int cnt1,cnt2,len,toggle=0; 1493 int startcnt=1; 1494 unsigned char c,hex; 1495 1496 if(argc>1&&(strcmp(argv[1],"-a")==0)) 1497 startcnt=2; 1498 printf("Decoded Hex:="); 1499 for(cnt1=startcnt;cnt1<argc;cnt1++) 1500 { 1501 len=strlen(argv[cnt1]); 1502 for(cnt2=0;cnt2<len;cnt2++) 1503 { 1504 c=argv[cnt1][cnt2]; 1505 if(c>='0'&&c<='9') 1506 c=c-'0'; 1507 if(c>='A'&&c<='F') 1508 c=c-'A'+10; 1509 if(c>='a'&&c<='f') 1510 c=c-'a'+10; 1511 switch(toggle) 1512 { 1513 case 0: 1514 hex=c<<4; 1515 toggle=1; 1516 break; 1517 case 1: 1518 hex+=c; 1519 if(hex<32||hex>127) 1520 { 1521 if(startcnt==1) 1522 printf("0x%02X ",(int)hex); 1523 else 1524 printf("."); 1525 } 1526 else 1527 { 1528 printf("%c",hex); 1529 if(startcnt==1) 1530 printf(" "); 1531 } 1532 toggle=0; 1533 break; 1534 } 1535 } 1536 } 1537 printf("\n"); 1538} 1539 1540 1541 1542 1543Stack tracing under VM 1544---------------------- 1545A basic backtrace 1546----------------- 1547 1548Here are the tricks I use 9 out of 10 times it works pretty well, 1549 1550When your backchain reaches a dead end 1551-------------------------------------- 1552This can happen when an exception happens in the kernel & the kernel is entered twice 1553if you reach the NULL pointer at the end of the back chain you should be 1554able to sniff further back if you follow the following tricks. 15551) A kernel address should be easy to recognise since it is in 1556primary space & the problem state bit isn't set & also 1557The Hi bit of the address is set. 15582) Another backchain should also be easy to recognise since it is an 1559address pointing to another address approximately 100 bytes or 0x70 hex 1560behind the current stackpointer. 1561 1562 1563Here is some practice. 1564boot the kernel & hit PA1 at some random time 1565d g to display the gprs, this should display something like 1566GPR 0 = 00000001 00156018 0014359C 00000000 1567GPR 4 = 00000001 001B8888 000003E0 00000000 1568GPR 8 = 00100080 00100084 00000000 000FE000 1569GPR 12 = 00010400 8001B2DC 8001B36A 000FFED8 1570Note that GPR14 is a return address but as we are real men we are going to 1571trace the stack. 1572display 0x40 bytes after the stack pointer. 1573 1574V000FFED8 000FFF38 8001B838 80014C8E 000FFF38 1575V000FFEE8 00000000 00000000 000003E0 00000000 1576V000FFEF8 00100080 00100084 00000000 000FE000 1577V000FFF08 00010400 8001B2DC 8001B36A 000FFED8 1578 1579 1580Ah now look at whats in sp+56 (sp+0x38) this is 8001B36A our saved r14 if 1581you look above at our stackframe & also agrees with GPR14. 1582 1583now backchain 1584d 000FFF38.40 1585we now are taking the contents of SP to get our first backchain. 1586 1587V000FFF38 000FFFA0 00000000 00014995 00147094 1588V000FFF48 00147090 001470A0 000003E0 00000000 1589V000FFF58 00100080 00100084 00000000 001BF1D0 1590V000FFF68 00010400 800149BA 80014CA6 000FFF38 1591 1592This displays a 2nd return address of 80014CA6 1593 1594now do d 000FFFA0.40 for our 3rd backchain 1595 1596V000FFFA0 04B52002 0001107F 00000000 00000000 1597V000FFFB0 00000000 00000000 FF000000 0001107F 1598V000FFFC0 00000000 00000000 00000000 00000000 1599V000FFFD0 00010400 80010802 8001085A 000FFFA0 1600 1601 1602our 3rd return address is 8001085A 1603 1604as the 04B52002 looks suspiciously like rubbish it is fair to assume that the kernel entry routines 1605for the sake of optimisation don't set up a backchain. 1606 1607now look at System.map to see if the addresses make any sense. 1608 1609grep -i 0001b3 System.map 1610outputs among other things 16110001b304 T cpu_idle 1612so 8001B36A 1613is cpu_idle+0x66 ( quiet the cpu is asleep, don't wake it ) 1614 1615 1616grep -i 00014 System.map 1617produces among other things 161800014a78 T start_kernel 1619so 0014CA6 is start_kernel+some hex number I can't add in my head. 1620 1621grep -i 00108 System.map 1622this produces 162300010800 T _stext 1624so 8001085A is _stext+0x5a 1625 1626Congrats you've done your first backchain. 1627 1628 1629 1630s/390 & z/Architecture IO Overview 1631================================== 1632 1633I am not going to give a course in 390 IO architecture as this would take me quite a 1634while & I'm no expert. Instead I'll give a 390 IO architecture summary for Dummies if you have 1635the s/390 principles of operation available read this instead. If nothing else you may find a few 1636useful keywords in here & be able to use them on a web search engine like altavista to find 1637more useful information. 1638 1639Unlike other bus architectures modern 390 systems do their IO using mostly 1640fibre optics & devices such as tapes & disks can be shared between several mainframes, 1641also S390 can support up to 65536 devices while a high end PC based system might be choking 1642with around 64. Here is some of the common IO terminology 1643 1644Subchannel: 1645This is the logical number most IO commands use to talk to an IO device there can be up to 16460x10000 (65536) of these in a configuration typically there is a few hundred. Under VM 1647for simplicity they are allocated contiguously, however on the native hardware they are not 1648they typically stay consistent between boots provided no new hardware is inserted or removed. 1649Under Linux for 390 we use these as IRQ's & also when issuing an IO command (CLEAR SUBCHANNEL, 1650HALT SUBCHANNEL,MODIFY SUBCHANNEL,RESUME SUBCHANNEL,START SUBCHANNEL,STORE SUBCHANNEL & 1651TEST SUBCHANNEL ) we use this as the ID of the device we wish to talk to, the most 1652important of these instructions are START SUBCHANNEL ( to start IO ), TEST SUBCHANNEL ( to check 1653whether the IO completed successfully ), & HALT SUBCHANNEL ( to kill IO ), a subchannel 1654can have up to 8 channel paths to a device this offers redundancy if one is not available. 1655 1656 1657Device Number: 1658This number remains static & Is closely tied to the hardware, there are 65536 of these 1659also they are made up of a CHPID ( Channel Path ID, the most significant 8 bits ) 1660& another lsb 8 bits. These remain static even if more devices are inserted or removed 1661from the hardware, there is a 1 to 1 mapping between Subchannels & Device Numbers provided 1662devices aren't inserted or removed. 1663 1664Channel Control Words: 1665CCWS are linked lists of instructions initially pointed to by an operation request block (ORB), 1666which is initially given to Start Subchannel (SSCH) command along with the subchannel number 1667for the IO subsystem to process while the CPU continues executing normal code. 1668These come in two flavours, Format 0 ( 24 bit for backward ) 1669compatibility & Format 1 ( 31 bit ). These are typically used to issue read & write 1670( & many other instructions ) they consist of a length field & an absolute address field. 1671For each IO typically get 1 or 2 interrupts one for channel end ( primary status ) when the 1672channel is idle & the second for device end ( secondary status ) sometimes you get both 1673concurrently, you check how the IO went on by issuing a TEST SUBCHANNEL at each interrupt, 1674from which you receive an Interruption response block (IRB). If you get channel & device end 1675status in the IRB without channel checks etc. your IO probably went okay. If you didn't you 1676probably need a doctor to examine the IRB & extended status word etc. 1677If an error occurs, more sophisticated control units have a facility known as 1678concurrent sense this means that if an error occurs Extended sense information will 1679be presented in the Extended status word in the IRB if not you have to issue a 1680subsequent SENSE CCW command after the test subchannel. 1681 1682 1683TPI( Test pending interrupt) can also be used for polled IO but in multitasking multiprocessor 1684systems it isn't recommended except for checking special cases ( i.e. non looping checks for 1685pending IO etc. ). 1686 1687Store Subchannel & Modify Subchannel can be used to examine & modify operating characteristics 1688of a subchannel ( e.g. channel paths ). 1689 1690Other IO related Terms: 1691Sysplex: S390's Clustering Technology 1692QDIO: S390's new high speed IO architecture to support devices such as gigabit ethernet, 1693this architecture is also designed to be forward compatible with up & coming 64 bit machines. 1694 1695 1696General Concepts 1697 1698Input Output Processors (IOP's) are responsible for communicating between 1699the mainframe CPU's & the channel & relieve the mainframe CPU's from the 1700burden of communicating with IO devices directly, this allows the CPU's to 1701concentrate on data processing. 1702 1703IOP's can use one or more links ( known as channel paths ) to talk to each 1704IO device. It first checks for path availability & chooses an available one, 1705then starts ( & sometimes terminates IO ). 1706There are two types of channel path: ESCON & the Parallel IO interface. 1707 1708IO devices are attached to control units, control units provide the 1709logic to interface the channel paths & channel path IO protocols to 1710the IO devices, they can be integrated with the devices or housed separately 1711& often talk to several similar devices ( typical examples would be raid 1712controllers or a control unit which connects to 1000 3270 terminals ). 1713 1714 1715 +---------------------------------------------------------------+ 1716 | +-----+ +-----+ +-----+ +-----+ +----------+ +----------+ | 1717 | | CPU | | CPU | | CPU | | CPU | | Main | | Expanded | | 1718 | | | | | | | | | | Memory | | Storage | | 1719 | +-----+ +-----+ +-----+ +-----+ +----------+ +----------+ | 1720 |---------------------------------------------------------------+ 1721 | IOP | IOP | IOP | 1722 |--------------------------------------------------------------- 1723 | C | C | C | C | C | C | C | C | C | C | C | C | C | C | C | C | 1724 ---------------------------------------------------------------- 1725 || || 1726 || Bus & Tag Channel Path || ESCON 1727 || ====================== || Channel 1728 || || || || Path 1729 +----------+ +----------+ +----------+ 1730 | | | | | | 1731 | CU | | CU | | CU | 1732 | | | | | | 1733 +----------+ +----------+ +----------+ 1734 | | | | | 1735+----------+ +----------+ +----------+ +----------+ +----------+ 1736|I/O Device| |I/O Device| |I/O Device| |I/O Device| |I/O Device| 1737+----------+ +----------+ +----------+ +----------+ +----------+ 1738 CPU = Central Processing Unit 1739 C = Channel 1740 IOP = IP Processor 1741 CU = Control Unit 1742 1743The 390 IO systems come in 2 flavours the current 390 machines support both 1744 1745The Older 360 & 370 Interface,sometimes called the Parallel I/O interface, 1746sometimes called Bus-and Tag & sometimes Original Equipment Manufacturers 1747Interface (OEMI). 1748 1749This byte wide Parallel channel path/bus has parity & data on the "Bus" cable 1750& control lines on the "Tag" cable. These can operate in byte multiplex mode for 1751sharing between several slow devices or burst mode & monopolize the channel for the 1752whole burst. Up to 256 devices can be addressed on one of these cables. These cables are 1753about one inch in diameter. The maximum unextended length supported by these cables is 1754125 Meters but this can be extended up to 2km with a fibre optic channel extended 1755such as a 3044. The maximum burst speed supported is 4.5 megabytes per second however 1756some really old processors support only transfer rates of 3.0, 2.0 & 1.0 MB/sec. 1757One of these paths can be daisy chained to up to 8 control units. 1758 1759 1760ESCON if fibre optic it is also called FICON 1761Was introduced by IBM in 1990. Has 2 fibre optic cables & uses either leds or lasers 1762for communication at a signaling rate of up to 200 megabits/sec. As 10bits are transferred 1763for every 8 bits info this drops to 160 megabits/sec & to 18.6 Megabytes/sec once 1764control info & CRC are added. ESCON only operates in burst mode. 1765 1766ESCONs typical max cable length is 3km for the led version & 20km for the laser version 1767known as XDF ( extended distance facility ). This can be further extended by using an 1768ESCON director which triples the above mentioned ranges. Unlike Bus & Tag as ESCON is 1769serial it uses a packet switching architecture the standard Bus & Tag control protocol 1770is however present within the packets. Up to 256 devices can be attached to each control 1771unit that uses one of these interfaces. 1772 1773Common 390 Devices include: 1774Network adapters typically OSA2,3172's,2116's & OSA-E gigabit ethernet adapters, 1775Consoles 3270 & 3215 ( a teletype emulated under linux for a line mode console ). 1776DASD's direct access storage devices ( otherwise known as hard disks ). 1777Tape Drives. 1778CTC ( Channel to Channel Adapters ), 1779ESCON or Parallel Cables used as a very high speed serial link 1780between 2 machines. We use 2 cables under linux to do a bi-directional serial link. 1781 1782 1783Debugging IO on s/390 & z/Architecture under VM 1784=============================================== 1785 1786Now we are ready to go on with IO tracing commands under VM 1787 1788A few self explanatory queries: 1789Q OSA 1790Q CTC 1791Q DISK ( This command is CMS specific ) 1792Q DASD 1793 1794 1795 1796 1797 1798 1799Q OSA on my machine returns 1800OSA 7C08 ON OSA 7C08 SUBCHANNEL = 0000 1801OSA 7C09 ON OSA 7C09 SUBCHANNEL = 0001 1802OSA 7C14 ON OSA 7C14 SUBCHANNEL = 0002 1803OSA 7C15 ON OSA 7C15 SUBCHANNEL = 0003 1804 1805If you have a guest with certain privileges you may be able to see devices 1806which don't belong to you. To avoid this, add the option V. 1807e.g. 1808Q V OSA 1809 1810Now using the device numbers returned by this command we will 1811Trace the io starting up on the first device 7c08 & 7c09 1812In our simplest case we can trace the 1813start subchannels 1814like TR SSCH 7C08-7C09 1815or the halt subchannels 1816or TR HSCH 7C08-7C09 1817MSCH's ,STSCH's I think you can guess the rest 1818 1819Ingo's favourite trick is tracing all the IO's & CCWS & spooling them into the reader of another 1820VM guest so he can ftp the logfile back to his own machine.I'll do a small bit of this & give you 1821 a look at the output. 1822 18231) Spool stdout to VM reader 1824SP PRT TO (another vm guest ) or * for the local vm guest 18252) Fill the reader with the trace 1826TR IO 7c08-7c09 INST INT CCW PRT RUN 18273) Start up linux 1828i 00c 18294) Finish the trace 1830TR END 18315) close the reader 1832C PRT 18336) list reader contents 1834RDRLIST 18357) copy it to linux4's minidisk 1836RECEIVE / LOG TXT A1 ( replace 18378) 1838filel & press F11 to look at it 1839You should see something like: 1840 184100020942' SSCH B2334000 0048813C CC 0 SCH 0000 DEV 7C08 1842 CPA 000FFDF0 PARM 00E2C9C4 KEY 0 FPI C0 LPM 80 1843 CCW 000FFDF0 E4200100 00487FE8 0000 E4240100 ........ 1844 IDAL 43D8AFE8 1845 IDAL 0FB76000 184600020B0A' I/O DEV 7C08 -> 000197BC' SCH 0000 PARM 00E2C9C4 184700021628' TSCH B2354000 >> 00488164 CC 0 SCH 0000 DEV 7C08 1848 CCWA 000FFDF8 DEV STS 0C SCH STS 00 CNT 00EC 1849 KEY 0 FPI C0 CC 0 CTLS 4007 185000022238' STSCH B2344000 >> 00488108 CC 0 SCH 0000 DEV 7C08 1851 1852If you don't like messing up your readed ( because you possibly booted from it ) 1853you can alternatively spool it to another readers guest. 1854 1855 1856Other common VM device related commands 1857--------------------------------------------- 1858These commands are listed only because they have 1859been of use to me in the past & may be of use to 1860you too. For more complete info on each of the commands 1861use type HELP <command> from CMS. 1862detaching devices 1863DET <devno range> 1864ATT <devno range> <guest> 1865attach a device to guest * for your own guest 1866READY <devno> cause VM to issue a fake interrupt. 1867 1868The VARY command is normally only available to VM administrators. 1869VARY ON PATH <path> TO <devno range> 1870VARY OFF PATH <PATH> FROM <devno range> 1871This is used to switch on or off channel paths to devices. 1872 1873Q CHPID <channel path ID> 1874This displays state of devices using this channel path 1875D SCHIB <subchannel> 1876This displays the subchannel information SCHIB block for the device. 1877this I believe is also only available to administrators. 1878DEFINE CTC <devno> 1879defines a virtual CTC channel to channel connection 18802 need to be defined on each guest for the CTC driver to use. 1881COUPLE devno userid remote devno 1882Joins a local virtual device to a remote virtual device 1883( commonly used for the CTC driver ). 1884 1885Building a VM ramdisk under CMS which linux can use 1886def vfb-<blocksize> <subchannel> <number blocks> 1887blocksize is commonly 4096 for linux. 1888Formatting it 1889format <subchannel> <driver letter e.g. x> (blksize <blocksize> 1890 1891Sharing a disk between multiple guests 1892LINK userid devno1 devno2 mode password 1893 1894 1895 1896GDB on S390 1897=========== 1898N.B. if compiling for debugging gdb works better without optimisation 1899( see Compiling programs for debugging ) 1900 1901invocation 1902---------- 1903gdb <victim program> <optional corefile> 1904 1905Online help 1906----------- 1907help: gives help on commands 1908e.g. 1909help 1910help display 1911Note gdb's online help is very good use it. 1912 1913 1914Assembly 1915-------- 1916info registers: displays registers other than floating point. 1917info all-registers: displays floating points as well. 1918disassemble: disassembles 1919e.g. 1920disassemble without parameters will disassemble the current function 1921disassemble $pc $pc+10 1922 1923Viewing & modifying variables 1924----------------------------- 1925print or p: displays variable or register 1926e.g. p/x $sp will display the stack pointer 1927 1928display: prints variable or register each time program stops 1929e.g. 1930display/x $pc will display the program counter 1931display argc 1932 1933undisplay : undo's display's 1934 1935info breakpoints: shows all current breakpoints 1936 1937info stack: shows stack back trace ( if this doesn't work too well, I'll show you the 1938stacktrace by hand below ). 1939 1940info locals: displays local variables. 1941 1942info args: display current procedure arguments. 1943 1944set args: will set argc & argv each time the victim program is invoked. 1945 1946set <variable>=value 1947set argc=100 1948set $pc=0 1949 1950 1951 1952Modifying execution 1953------------------- 1954step: steps n lines of sourcecode 1955step steps 1 line. 1956step 100 steps 100 lines of code. 1957 1958next: like step except this will not step into subroutines 1959 1960stepi: steps a single machine code instruction. 1961e.g. stepi 100 1962 1963nexti: steps a single machine code instruction but will not step into subroutines. 1964 1965finish: will run until exit of the current routine 1966 1967run: (re)starts a program 1968 1969cont: continues a program 1970 1971quit: exits gdb. 1972 1973 1974breakpoints 1975------------ 1976 1977break 1978sets a breakpoint 1979e.g. 1980 1981break main 1982 1983break *$pc 1984 1985break *0x400618 1986 1987heres a really useful one for large programs 1988rbr 1989Set a breakpoint for all functions matching REGEXP 1990e.g. 1991rbr 390 1992will set a breakpoint with all functions with 390 in their name. 1993 1994info breakpoints 1995lists all breakpoints 1996 1997delete: delete breakpoint by number or delete them all 1998e.g. 1999delete 1 will delete the first breakpoint 2000delete will delete them all 2001 2002watch: This will set a watchpoint ( usually hardware assisted ), 2003This will watch a variable till it changes 2004e.g. 2005watch cnt, will watch the variable cnt till it changes. 2006As an aside unfortunately gdb's, architecture independent watchpoint code 2007is inconsistent & not very good, watchpoints usually work but not always. 2008 2009info watchpoints: Display currently active watchpoints 2010 2011condition: ( another useful one ) 2012Specify breakpoint number N to break only if COND is true. 2013Usage is `condition N COND', where N is an integer and COND is an 2014expression to be evaluated whenever breakpoint N is reached. 2015 2016 2017 2018User defined functions/macros 2019----------------------------- 2020define: ( Note this is very very useful,simple & powerful ) 2021usage define <name> <list of commands> end 2022 2023examples which you should consider putting into .gdbinit in your home directory 2024define d 2025stepi 2026disassemble $pc $pc+10 2027end 2028 2029define e 2030nexti 2031disassemble $pc $pc+10 2032end 2033 2034 2035Other hard to classify stuff 2036---------------------------- 2037signal n: 2038sends the victim program a signal. 2039e.g. signal 3 will send a SIGQUIT. 2040 2041info signals: 2042what gdb does when the victim receives certain signals. 2043 2044list: 2045e.g. 2046list lists current function source 2047list 1,10 list first 10 lines of current file. 2048list test.c:1,10 2049 2050 2051directory: 2052Adds directories to be searched for source if gdb cannot find the source. 2053(note it is a bit sensitive about slashes) 2054e.g. To add the root of the filesystem to the searchpath do 2055directory // 2056 2057 2058call <function> 2059This calls a function in the victim program, this is pretty powerful 2060e.g. 2061(gdb) call printf("hello world") 2062outputs: 2063$1 = 11 2064 2065You might now be thinking that the line above didn't work, something extra had to be done. 2066(gdb) call fflush(stdout) 2067hello world$2 = 0 2068As an aside the debugger also calls malloc & free under the hood 2069to make space for the "hello world" string. 2070 2071 2072 2073hints 2074----- 20751) command completion works just like bash 2076( if you are a bad typist like me this really helps ) 2077e.g. hit br <TAB> & cursor up & down :-). 2078 20792) if you have a debugging problem that takes a few steps to recreate 2080put the steps into a file called .gdbinit in your current working directory 2081if you have defined a few extra useful user defined commands put these in 2082your home directory & they will be read each time gdb is launched. 2083 2084A typical .gdbinit file might be. 2085break main 2086run 2087break runtime_exception 2088cont 2089 2090 2091stack chaining in gdb by hand 2092----------------------------- 2093This is done using a the same trick described for VM 2094p/x (*($sp+56))&0x7fffffff get the first backchain. 2095 2096For z/Architecture 2097Replace 56 with 112 & ignore the &0x7fffffff 2098in the macros below & do nasty casts to longs like the following 2099as gdb unfortunately deals with printed arguments as ints which 2100messes up everything. 2101i.e. here is a 3rd backchain dereference 2102p/x *(long *)(***(long ***)$sp+112) 2103 2104 2105this outputs 2106$5 = 0x528f18 2107on my machine. 2108Now you can use 2109info symbol (*($sp+56))&0x7fffffff 2110you might see something like. 2111rl_getc + 36 in section .text telling you what is located at address 0x528f18 2112Now do. 2113p/x (*(*$sp+56))&0x7fffffff 2114This outputs 2115$6 = 0x528ed0 2116Now do. 2117info symbol (*(*$sp+56))&0x7fffffff 2118rl_read_key + 180 in section .text 2119now do 2120p/x (*(**$sp+56))&0x7fffffff 2121& so on. 2122 2123Disassembling instructions without debug info 2124--------------------------------------------- 2125gdb typically complains if there is a lack of debugging 2126symbols in the disassemble command with 2127"No function contains specified address." To get around 2128this do 2129x/<number lines to disassemble>xi <address> 2130e.g. 2131x/20xi 0x400730 2132 2133 2134 2135Note: Remember gdb has history just like bash you don't need to retype the 2136whole line just use the up & down arrows. 2137 2138 2139 2140For more info 2141------------- 2142From your linuxbox do 2143man gdb or info gdb. 2144 2145core dumps 2146---------- 2147What a core dump ?, 2148A core dump is a file generated by the kernel ( if allowed ) which contains the registers, 2149& all active pages of the program which has crashed. 2150From this file gdb will allow you to look at the registers & stack trace & memory of the 2151program as if it just crashed on your system, it is usually called core & created in the 2152current working directory. 2153This is very useful in that a customer can mail a core dump to a technical support department 2154& the technical support department can reconstruct what happened. 2155Provided they have an identical copy of this program with debugging symbols compiled in & 2156the source base of this build is available. 2157In short it is far more useful than something like a crash log could ever hope to be. 2158 2159In theory all that is missing to restart a core dumped program is a kernel patch which 2160will do the following. 21611) Make a new kernel task structure 21622) Reload all the dumped pages back into the kernel's memory management structures. 21633) Do the required clock fixups 21644) Get all files & network connections for the process back into an identical state ( really difficult ). 21655) A few more difficult things I haven't thought of. 2166 2167 2168 2169Why have I never seen one ?. 2170Probably because you haven't used the command 2171ulimit -c unlimited in bash 2172to allow core dumps, now do 2173ulimit -a 2174to verify that the limit was accepted. 2175 2176A sample core dump 2177To create this I'm going to do 2178ulimit -c unlimited 2179gdb 2180to launch gdb (my victim app. ) now be bad & do the following from another 2181telnet/xterm session to the same machine 2182ps -aux | grep gdb 2183kill -SIGSEGV <gdb's pid> 2184or alternatively use killall -SIGSEGV gdb if you have the killall command. 2185Now look at the core dump. 2186./gdb core 2187Displays the following 2188GNU gdb 4.18 2189Copyright 1998 Free Software Foundation, Inc. 2190GDB is free software, covered by the GNU General Public License, and you are 2191welcome to change it and/or distribute copies of it under certain conditions. 2192Type "show copying" to see the conditions. 2193There is absolutely no warranty for GDB. Type "show warranty" for details. 2194This GDB was configured as "s390-ibm-linux"... 2195Core was generated by `./gdb'. 2196Program terminated with signal 11, Segmentation fault. 2197Reading symbols from /usr/lib/libncurses.so.4...done. 2198Reading symbols from /lib/libm.so.6...done. 2199Reading symbols from /lib/libc.so.6...done. 2200Reading symbols from /lib/ld-linux.so.2...done. 2201#0 0x40126d1a in read () from /lib/libc.so.6 2202Setting up the environment for debugging gdb. 2203Breakpoint 1 at 0x4dc6f8: file utils.c, line 471. 2204Breakpoint 2 at 0x4d87a4: file top.c, line 2609. 2205(top-gdb) info stack 2206#0 0x40126d1a in read () from /lib/libc.so.6 2207#1 0x528f26 in rl_getc (stream=0x7ffffde8) at input.c:402 2208#2 0x528ed0 in rl_read_key () at input.c:381 2209#3 0x5167e6 in readline_internal_char () at readline.c:454 2210#4 0x5168ee in readline_internal_charloop () at readline.c:507 2211#5 0x51692c in readline_internal () at readline.c:521 2212#6 0x5164fe in readline (prompt=0x7ffff810 "\177��������x\177������������\177��������x����") 2213 at readline.c:349 2214#7 0x4d7a8a in command_line_input (prrompt=0x564420 "(gdb) ", repeat=1, 2215 annotation_suffix=0x4d6b44 "prompt") at top.c:2091 2216#8 0x4d6cf0 in command_loop () at top.c:1345 2217#9 0x4e25bc in main (argc=1, argv=0x7ffffdf4) at main.c:635 2218 2219 2220LDD 2221=== 2222This is a program which lists the shared libraries which a library needs, 2223Note you also get the relocations of the shared library text segments which 2224help when using objdump --source. 2225e.g. 2226 ldd ./gdb 2227outputs 2228libncurses.so.4 => /usr/lib/libncurses.so.4 (0x40018000) 2229libm.so.6 => /lib/libm.so.6 (0x4005e000) 2230libc.so.6 => /lib/libc.so.6 (0x40084000) 2231/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000) 2232 2233 2234Debugging shared libraries 2235========================== 2236Most programs use shared libraries, however it can be very painful 2237when you single step instruction into a function like printf for the 2238first time & you end up in functions like _dl_runtime_resolve this is 2239the ld.so doing lazy binding, lazy binding is a concept in ELF where 2240shared library functions are not loaded into memory unless they are 2241actually used, great for saving memory but a pain to debug. 2242To get around this either relink the program -static or exit gdb type 2243export LD_BIND_NOW=true this will stop lazy binding & restart the gdb'ing 2244the program in question. 2245 2246 2247 2248Debugging modules 2249================= 2250As modules are dynamically loaded into the kernel their address can be 2251anywhere to get around this use the -m option with insmod to emit a load 2252map which can be piped into a file if required. 2253 2254The proc file system 2255==================== 2256What is it ?. 2257It is a filesystem created by the kernel with files which are created on demand 2258by the kernel if read, or can be used to modify kernel parameters, 2259it is a powerful concept. 2260 2261e.g. 2262 2263cat /proc/sys/net/ipv4/ip_forward 2264On my machine outputs 22650 2266telling me ip_forwarding is not on to switch it on I can do 2267echo 1 > /proc/sys/net/ipv4/ip_forward 2268cat it again 2269cat /proc/sys/net/ipv4/ip_forward 2270On my machine now outputs 22711 2272IP forwarding is on. 2273There is a lot of useful info in here best found by going in & having a look around, 2274so I'll take you through some entries I consider important. 2275 2276All the processes running on the machine have there own entry defined by 2277/proc/<pid> 2278So lets have a look at the init process 2279cd /proc/1 2280 2281cat cmdline 2282emits 2283init [2] 2284 2285cd /proc/1/fd 2286This contains numerical entries of all the open files, 2287some of these you can cat e.g. stdout (2) 2288 2289cat /proc/29/maps 2290on my machine emits 2291 229200400000-00478000 r-xp 00000000 5f:00 4103 /bin/bash 229300478000-0047e000 rw-p 00077000 5f:00 4103 /bin/bash 22940047e000-00492000 rwxp 00000000 00:00 0 229540000000-40015000 r-xp 00000000 5f:00 14382 /lib/ld-2.1.2.so 229640015000-40016000 rw-p 00014000 5f:00 14382 /lib/ld-2.1.2.so 229740016000-40017000 rwxp 00000000 00:00 0 229840017000-40018000 rw-p 00000000 00:00 0 229940018000-4001b000 r-xp 00000000 5f:00 14435 /lib/libtermcap.so.2.0.8 23004001b000-4001c000 rw-p 00002000 5f:00 14435 /lib/libtermcap.so.2.0.8 23014001c000-4010d000 r-xp 00000000 5f:00 14387 /lib/libc-2.1.2.so 23024010d000-40111000 rw-p 000f0000 5f:00 14387 /lib/libc-2.1.2.so 230340111000-40114000 rw-p 00000000 00:00 0 230440114000-4011e000 r-xp 00000000 5f:00 14408 /lib/libnss_files-2.1.2.so 23054011e000-4011f000 rw-p 00009000 5f:00 14408 /lib/libnss_files-2.1.2.so 23067fffd000-80000000 rwxp ffffe000 00:00 0 2307 2308 2309Showing us the shared libraries init uses where they are in memory 2310& memory access permissions for each virtual memory area. 2311 2312/proc/1/cwd is a softlink to the current working directory. 2313/proc/1/root is the root of the filesystem for this process. 2314 2315/proc/1/mem is the current running processes memory which you 2316can read & write to like a file. 2317strace uses this sometimes as it is a bit faster than the 2318rather inefficient ptrace interface for peeking at DATA. 2319 2320 2321cat status 2322 2323Name: init 2324State: S (sleeping) 2325Pid: 1 2326PPid: 0 2327Uid: 0 0 0 0 2328Gid: 0 0 0 0 2329Groups: 2330VmSize: 408 kB 2331VmLck: 0 kB 2332VmRSS: 208 kB 2333VmData: 24 kB 2334VmStk: 8 kB 2335VmExe: 368 kB 2336VmLib: 0 kB 2337SigPnd: 0000000000000000 2338SigBlk: 0000000000000000 2339SigIgn: 7fffffffd7f0d8fc 2340SigCgt: 00000000280b2603 2341CapInh: 00000000fffffeff 2342CapPrm: 00000000ffffffff 2343CapEff: 00000000fffffeff 2344 2345User PSW: 070de000 80414146 2346task: 004b6000 tss: 004b62d8 ksp: 004b7ca8 pt_regs: 004b7f68 2347User GPRS: 234800000400 00000000 0000000b 7ffffa90 234900000000 00000000 00000000 0045d9f4 23500045cafc 7ffffa90 7fffff18 0045cb08 235100010400 804039e8 80403af8 7ffff8b0 2352User ACRS: 235300000000 00000000 00000000 00000000 235400000001 00000000 00000000 00000000 235500000000 00000000 00000000 00000000 235600000000 00000000 00000000 00000000 2357Kernel BackChain CallChain BackChain CallChain 2358 004b7ca8 8002bd0c 004b7d18 8002b92c 2359 004b7db8 8005cd50 004b7e38 8005d12a 2360 004b7f08 80019114 2361Showing among other things memory usage & status of some signals & 2362the processes'es registers from the kernel task_structure 2363as well as a backchain which may be useful if a process crashes 2364in the kernel for some unknown reason. 2365 2366Some driver debugging techniques 2367================================ 2368debug feature 2369------------- 2370Some of our drivers now support a "debug feature" in 2371/proc/s390dbf see s390dbf.txt in the linux/Documentation directory 2372for more info. 2373e.g. 2374to switch on the lcs "debug feature" 2375echo 5 > /proc/s390dbf/lcs/level 2376& then after the error occurred. 2377cat /proc/s390dbf/lcs/sprintf >/logfile 2378the logfile now contains some information which may help 2379tech support resolve a problem in the field. 2380 2381 2382 2383high level debugging network drivers 2384------------------------------------ 2385ifconfig is a quite useful command 2386it gives the current state of network drivers. 2387 2388If you suspect your network device driver is dead 2389one way to check is type 2390ifconfig <network device> 2391e.g. tr0 2392You should see something like 2393tr0 Link encap:16/4 Mbps Token Ring (New) HWaddr 00:04:AC:20:8E:48 2394 inet addr:9.164.185.132 Bcast:9.164.191.255 Mask:255.255.224.0 2395 UP BROADCAST RUNNING MULTICAST MTU:2000 Metric:1 2396 RX packets:246134 errors:0 dropped:0 overruns:0 frame:0 2397 TX packets:5 errors:0 dropped:0 overruns:0 carrier:0 2398 collisions:0 txqueuelen:100 2399 2400if the device doesn't say up 2401try 2402/etc/rc.d/init.d/network start 2403( this starts the network stack & hopefully calls ifconfig tr0 up ). 2404ifconfig looks at the output of /proc/net/dev & presents it in a more presentable form 2405Now ping the device from a machine in the same subnet. 2406if the RX packets count & TX packets counts don't increment you probably 2407have problems. 2408next 2409cat /proc/net/arp 2410Do you see any hardware addresses in the cache if not you may have problems. 2411Next try 2412ping -c 5 <broadcast_addr> i.e. the Bcast field above in the output of 2413ifconfig. Do you see any replies from machines other than the local machine 2414if not you may have problems. also if the TX packets count in ifconfig 2415hasn't incremented either you have serious problems in your driver 2416(e.g. the txbusy field of the network device being stuck on ) 2417or you may have multiple network devices connected. 2418 2419 2420chandev 2421------- 2422There is a new device layer for channel devices, some 2423drivers e.g. lcs are registered with this layer. 2424If the device uses the channel device layer you'll be 2425able to find what interrupts it uses & the current state 2426of the device. 2427See the manpage chandev.8 &type cat /proc/chandev for more info. 2428 2429 2430 2431Starting points for debugging scripting languages etc. 2432====================================================== 2433 2434bash/sh 2435 2436bash -x <scriptname> 2437e.g. bash -x /usr/bin/bashbug 2438displays the following lines as it executes them. 2439+ MACHINE=i586 2440+ OS=linux-gnu 2441+ CC=gcc 2442+ CFLAGS= -DPROGRAM='bash' -DHOSTTYPE='i586' -DOSTYPE='linux-gnu' -DMACHTYPE='i586-pc-linux-gnu' -DSHELL -DHAVE_CONFIG_H -I. -I. -I./lib -O2 -pipe 2443+ RELEASE=2.01 2444+ PATCHLEVEL=1 2445+ RELSTATUS=release 2446+ MACHTYPE=i586-pc-linux-gnu 2447 2448perl -d <scriptname> runs the perlscript in a fully interactive debugger 2449<like gdb>. 2450Type 'h' in the debugger for help. 2451 2452for debugging java type 2453jdb <filename> another fully interactive gdb style debugger. 2454& type ? in the debugger for help. 2455 2456 2457 2458Dumptool & Lcrash ( lkcd ) 2459========================== 2460Michael Holzheu & others here at IBM have a fairly mature port of 2461SGI's lcrash tool which allows one to look at kernel structures in a 2462running kernel. 2463 2464It also complements a tool called dumptool which dumps all the kernel's 2465memory pages & registers to either a tape or a disk. 2466This can be used by tech support or an ambitious end user do 2467post mortem debugging of a machine like gdb core dumps. 2468 2469Going into how to use this tool in detail will be explained 2470in other documentation supplied by IBM with the patches & the 2471lcrash homepage http://oss.sgi.com/projects/lkcd/ & the lcrash manpage. 2472 2473How they work 2474------------- 2475Lcrash is a perfectly normal program,however, it requires 2 2476additional files, Kerntypes which is built using a patch to the 2477linux kernel sources in the linux root directory & the System.map. 2478 2479Kerntypes is an objectfile whose sole purpose in life 2480is to provide stabs debug info to lcrash, to do this 2481Kerntypes is built from kerntypes.c which just includes the most commonly 2482referenced header files used when debugging, lcrash can then read the 2483.stabs section of this file. 2484 2485Debugging a live system it uses /dev/mem 2486alternatively for post mortem debugging it uses the data 2487collected by dumptool. 2488 2489 2490 2491SysRq 2492===== 2493This is now supported by linux for s/390 & z/Architecture. 2494To enable it do compile the kernel with 2495Kernel Hacking -> Magic SysRq Key Enabled 2496echo "1" > /proc/sys/kernel/sysrq 2497also type 2498echo "8" >/proc/sys/kernel/printk 2499To make printk output go to console. 2500On 390 all commands are prefixed with 2501^- 2502e.g. 2503^-t will show tasks. 2504^-? or some unknown command will display help. 2505The sysrq key reading is very picky ( I have to type the keys in an 2506 xterm session & paste them into the x3270 console ) 2507& it may be wise to predefine the keys as described in the VM hints above 2508 2509This is particularly useful for syncing disks unmounting & rebooting 2510if the machine gets partially hung. 2511 2512Read Documentation/sysrq.txt for more info 2513 2514References: 2515=========== 2516Enterprise Systems Architecture Reference Summary 2517Enterprise Systems Architecture Principles of Operation 2518Hartmut Penners s390 stack frame sheet. 2519IBM Mainframe Channel Attachment a technology brief from a CISCO webpage 2520Various bits of man & info pages of Linux. 2521Linux & GDB source. 2522Various info & man pages. 2523CMS Help on tracing commands. 2524Linux for s/390 Elf Application Binary Interface 2525Linux for z/Series Elf Application Binary Interface ( Both Highly Recommended ) 2526z/Architecture Principles of Operation SA22-7832-00 2527Enterprise Systems Architecture/390 Reference Summary SA22-7209-01 & the 2528Enterprise Systems Architecture/390 Principles of Operation SA22-7201-05 2529 2530Special Thanks 2531============== 2532Special thanks to Neale Ferguson who maintains a much 2533prettier HTML version of this page at 2534http://penguinvm.princeton.edu/notes.html#Debug390 2535Bob Grainger Stefan Bader & others for reporting bugs 2536