alloca.c revision 33965
133965Sjdp/* alloca.c -- allocate automatically reclaimed memory 233965Sjdp (Mostly) portable public-domain implementation -- D A Gwyn 333965Sjdp 433965Sjdp This implementation of the PWB library alloca function, 533965Sjdp which is used to allocate space off the run-time stack so 633965Sjdp that it is automatically reclaimed upon procedure exit, 733965Sjdp was inspired by discussions with J. Q. Johnson of Cornell. 833965Sjdp J.Otto Tennant <jot@cray.com> contributed the Cray support. 933965Sjdp 1033965Sjdp There are some preprocessor constants that can 1133965Sjdp be defined when compiling for your specific system, for 1233965Sjdp improved efficiency; however, the defaults should be okay. 1333965Sjdp 1433965Sjdp The general concept of this implementation is to keep 1533965Sjdp track of all alloca-allocated blocks, and reclaim any 1633965Sjdp that are found to be deeper in the stack than the current 1733965Sjdp invocation. This heuristic does not reclaim storage as 1833965Sjdp soon as it becomes invalid, but it will do so eventually. 1933965Sjdp 2033965Sjdp As a special case, alloca(0) reclaims storage without 2133965Sjdp allocating any. It is a good idea to use alloca(0) in 2233965Sjdp your main control loop, etc. to force garbage collection. */ 2333965Sjdp 2433965Sjdp#ifdef HAVE_CONFIG_H 2533965Sjdp#include "config.h" 2633965Sjdp#endif 2733965Sjdp 2833965Sjdp/* If compiling with GCC, this file's not needed. */ 2933965Sjdp#ifndef alloca 3033965Sjdp 3133965Sjdp#ifdef emacs 3233965Sjdp#ifdef static 3333965Sjdp/* actually, only want this if static is defined as "" 3433965Sjdp -- this is for usg, in which emacs must undefine static 3533965Sjdp in order to make unexec workable 3633965Sjdp */ 3733965Sjdp#ifndef STACK_DIRECTION 3833965Sjdpyou 3933965Sjdplose 4033965Sjdp-- must know STACK_DIRECTION at compile-time 4133965Sjdp#endif /* STACK_DIRECTION undefined */ 4233965Sjdp#endif /* static */ 4333965Sjdp#endif /* emacs */ 4433965Sjdp 4533965Sjdp/* If your stack is a linked list of frames, you have to 4633965Sjdp provide an "address metric" ADDRESS_FUNCTION macro. */ 4733965Sjdp 4833965Sjdp#if defined (CRAY) && defined (CRAY_STACKSEG_END) 4933965Sjdplong i00afunc (); 5033965Sjdp#define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg)) 5133965Sjdp#else 5233965Sjdp#define ADDRESS_FUNCTION(arg) &(arg) 5333965Sjdp#endif 5433965Sjdp 5533965Sjdp#if __STDC__ 5633965Sjdp#include <stddef.h> 5733965Sjdptypedef void *pointer; 5833965Sjdp#else 5933965Sjdptypedef char *pointer; 6033965Sjdptypedef unsigned size_t; 6133965Sjdp#endif 6233965Sjdp 6333965Sjdp#ifndef NULL 6433965Sjdp#define NULL 0 6533965Sjdp#endif 6633965Sjdp 6733965Sjdp/* Different portions of Emacs need to call different versions of 6833965Sjdp malloc. The Emacs executable needs alloca to call xmalloc, because 6933965Sjdp ordinary malloc isn't protected from input signals. On the other 7033965Sjdp hand, the utilities in lib-src need alloca to call malloc; some of 7133965Sjdp them are very simple, and don't have an xmalloc routine. 7233965Sjdp 7333965Sjdp Non-Emacs programs expect this to call use xmalloc. 7433965Sjdp 7533965Sjdp Callers below should use malloc. */ 7633965Sjdp 7733965Sjdp#ifndef emacs 7833965Sjdp#define malloc xmalloc 7933965Sjdpextern pointer xmalloc (); 8033965Sjdp#endif 8133965Sjdp 8233965Sjdp/* Define STACK_DIRECTION if you know the direction of stack 8333965Sjdp growth for your system; otherwise it will be automatically 8433965Sjdp deduced at run-time. 8533965Sjdp 8633965Sjdp STACK_DIRECTION > 0 => grows toward higher addresses 8733965Sjdp STACK_DIRECTION < 0 => grows toward lower addresses 8833965Sjdp STACK_DIRECTION = 0 => direction of growth unknown */ 8933965Sjdp 9033965Sjdp#ifndef STACK_DIRECTION 9133965Sjdp#define STACK_DIRECTION 0 /* Direction unknown. */ 9233965Sjdp#endif 9333965Sjdp 9433965Sjdp#if STACK_DIRECTION != 0 9533965Sjdp 9633965Sjdp#define STACK_DIR STACK_DIRECTION /* Known at compile-time. */ 9733965Sjdp 9833965Sjdp#else /* STACK_DIRECTION == 0; need run-time code. */ 9933965Sjdp 10033965Sjdpstatic int stack_dir; /* 1 or -1 once known. */ 10133965Sjdp#define STACK_DIR stack_dir 10233965Sjdp 10333965Sjdpstatic void 10433965Sjdpfind_stack_direction () 10533965Sjdp{ 10633965Sjdp static char *addr = NULL; /* Address of first `dummy', once known. */ 10733965Sjdp auto char dummy; /* To get stack address. */ 10833965Sjdp 10933965Sjdp if (addr == NULL) 11033965Sjdp { /* Initial entry. */ 11133965Sjdp addr = ADDRESS_FUNCTION (dummy); 11233965Sjdp 11333965Sjdp find_stack_direction (); /* Recurse once. */ 11433965Sjdp } 11533965Sjdp else 11633965Sjdp { 11733965Sjdp /* Second entry. */ 11833965Sjdp if (ADDRESS_FUNCTION (dummy) > addr) 11933965Sjdp stack_dir = 1; /* Stack grew upward. */ 12033965Sjdp else 12133965Sjdp stack_dir = -1; /* Stack grew downward. */ 12233965Sjdp } 12333965Sjdp} 12433965Sjdp 12533965Sjdp#endif /* STACK_DIRECTION == 0 */ 12633965Sjdp 12733965Sjdp/* An "alloca header" is used to: 12833965Sjdp (a) chain together all alloca'ed blocks; 12933965Sjdp (b) keep track of stack depth. 13033965Sjdp 13133965Sjdp It is very important that sizeof(header) agree with malloc 13233965Sjdp alignment chunk size. The following default should work okay. */ 13333965Sjdp 13433965Sjdp#ifndef ALIGN_SIZE 13533965Sjdp#define ALIGN_SIZE sizeof(double) 13633965Sjdp#endif 13733965Sjdp 13833965Sjdptypedef union hdr 13933965Sjdp{ 14033965Sjdp char align[ALIGN_SIZE]; /* To force sizeof(header). */ 14133965Sjdp struct 14233965Sjdp { 14333965Sjdp union hdr *next; /* For chaining headers. */ 14433965Sjdp char *deep; /* For stack depth measure. */ 14533965Sjdp } h; 14633965Sjdp} header; 14733965Sjdp 14833965Sjdpstatic header *last_alloca_header = NULL; /* -> last alloca header. */ 14933965Sjdp 15033965Sjdp/* Return a pointer to at least SIZE bytes of storage, 15133965Sjdp which will be automatically reclaimed upon exit from 15233965Sjdp the procedure that called alloca. Originally, this space 15333965Sjdp was supposed to be taken from the current stack frame of the 15433965Sjdp caller, but that method cannot be made to work for some 15533965Sjdp implementations of C, for example under Gould's UTX/32. */ 15633965Sjdp 15733965Sjdppointer 15833965Sjdpalloca (size) 15933965Sjdp size_t size; 16033965Sjdp{ 16133965Sjdp auto char probe; /* Probes stack depth: */ 16233965Sjdp register char *depth = ADDRESS_FUNCTION (probe); 16333965Sjdp 16433965Sjdp#if STACK_DIRECTION == 0 16533965Sjdp if (STACK_DIR == 0) /* Unknown growth direction. */ 16633965Sjdp find_stack_direction (); 16733965Sjdp#endif 16833965Sjdp 16933965Sjdp /* Reclaim garbage, defined as all alloca'd storage that 17033965Sjdp was allocated from deeper in the stack than currently. */ 17133965Sjdp 17233965Sjdp { 17333965Sjdp register header *hp; /* Traverses linked list. */ 17433965Sjdp 17533965Sjdp for (hp = last_alloca_header; hp != NULL;) 17633965Sjdp if ((STACK_DIR > 0 && hp->h.deep > depth) 17733965Sjdp || (STACK_DIR < 0 && hp->h.deep < depth)) 17833965Sjdp { 17933965Sjdp register header *np = hp->h.next; 18033965Sjdp 18133965Sjdp free ((pointer) hp); /* Collect garbage. */ 18233965Sjdp 18333965Sjdp hp = np; /* -> next header. */ 18433965Sjdp } 18533965Sjdp else 18633965Sjdp break; /* Rest are not deeper. */ 18733965Sjdp 18833965Sjdp last_alloca_header = hp; /* -> last valid storage. */ 18933965Sjdp } 19033965Sjdp 19133965Sjdp if (size == 0) 19233965Sjdp return NULL; /* No allocation required. */ 19333965Sjdp 19433965Sjdp /* Allocate combined header + user data storage. */ 19533965Sjdp 19633965Sjdp { 19733965Sjdp register pointer new = malloc (sizeof (header) + size); 19833965Sjdp /* Address of header. */ 19933965Sjdp 20033965Sjdp ((header *) new)->h.next = last_alloca_header; 20133965Sjdp ((header *) new)->h.deep = depth; 20233965Sjdp 20333965Sjdp last_alloca_header = (header *) new; 20433965Sjdp 20533965Sjdp /* User storage begins just after header. */ 20633965Sjdp 20733965Sjdp return (pointer) ((char *) new + sizeof (header)); 20833965Sjdp } 20933965Sjdp} 21033965Sjdp 21133965Sjdp#if defined (CRAY) && defined (CRAY_STACKSEG_END) 21233965Sjdp 21333965Sjdp#ifdef DEBUG_I00AFUNC 21433965Sjdp#include <stdio.h> 21533965Sjdp#endif 21633965Sjdp 21733965Sjdp#ifndef CRAY_STACK 21833965Sjdp#define CRAY_STACK 21933965Sjdp#ifndef CRAY2 22033965Sjdp/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ 22133965Sjdpstruct stack_control_header 22233965Sjdp { 22333965Sjdp long shgrow:32; /* Number of times stack has grown. */ 22433965Sjdp long shaseg:32; /* Size of increments to stack. */ 22533965Sjdp long shhwm:32; /* High water mark of stack. */ 22633965Sjdp long shsize:32; /* Current size of stack (all segments). */ 22733965Sjdp }; 22833965Sjdp 22933965Sjdp/* The stack segment linkage control information occurs at 23033965Sjdp the high-address end of a stack segment. (The stack 23133965Sjdp grows from low addresses to high addresses.) The initial 23233965Sjdp part of the stack segment linkage control information is 23333965Sjdp 0200 (octal) words. This provides for register storage 23433965Sjdp for the routine which overflows the stack. */ 23533965Sjdp 23633965Sjdpstruct stack_segment_linkage 23733965Sjdp { 23833965Sjdp long ss[0200]; /* 0200 overflow words. */ 23933965Sjdp long sssize:32; /* Number of words in this segment. */ 24033965Sjdp long ssbase:32; /* Offset to stack base. */ 24133965Sjdp long:32; 24233965Sjdp long sspseg:32; /* Offset to linkage control of previous 24333965Sjdp segment of stack. */ 24433965Sjdp long:32; 24533965Sjdp long sstcpt:32; /* Pointer to task common address block. */ 24633965Sjdp long sscsnm; /* Private control structure number for 24733965Sjdp microtasking. */ 24833965Sjdp long ssusr1; /* Reserved for user. */ 24933965Sjdp long ssusr2; /* Reserved for user. */ 25033965Sjdp long sstpid; /* Process ID for pid based multi-tasking. */ 25133965Sjdp long ssgvup; /* Pointer to multitasking thread giveup. */ 25233965Sjdp long sscray[7]; /* Reserved for Cray Research. */ 25333965Sjdp long ssa0; 25433965Sjdp long ssa1; 25533965Sjdp long ssa2; 25633965Sjdp long ssa3; 25733965Sjdp long ssa4; 25833965Sjdp long ssa5; 25933965Sjdp long ssa6; 26033965Sjdp long ssa7; 26133965Sjdp long sss0; 26233965Sjdp long sss1; 26333965Sjdp long sss2; 26433965Sjdp long sss3; 26533965Sjdp long sss4; 26633965Sjdp long sss5; 26733965Sjdp long sss6; 26833965Sjdp long sss7; 26933965Sjdp }; 27033965Sjdp 27133965Sjdp#else /* CRAY2 */ 27233965Sjdp/* The following structure defines the vector of words 27333965Sjdp returned by the STKSTAT library routine. */ 27433965Sjdpstruct stk_stat 27533965Sjdp { 27633965Sjdp long now; /* Current total stack size. */ 27733965Sjdp long maxc; /* Amount of contiguous space which would 27833965Sjdp be required to satisfy the maximum 27933965Sjdp stack demand to date. */ 28033965Sjdp long high_water; /* Stack high-water mark. */ 28133965Sjdp long overflows; /* Number of stack overflow ($STKOFEN) calls. */ 28233965Sjdp long hits; /* Number of internal buffer hits. */ 28333965Sjdp long extends; /* Number of block extensions. */ 28433965Sjdp long stko_mallocs; /* Block allocations by $STKOFEN. */ 28533965Sjdp long underflows; /* Number of stack underflow calls ($STKRETN). */ 28633965Sjdp long stko_free; /* Number of deallocations by $STKRETN. */ 28733965Sjdp long stkm_free; /* Number of deallocations by $STKMRET. */ 28833965Sjdp long segments; /* Current number of stack segments. */ 28933965Sjdp long maxs; /* Maximum number of stack segments so far. */ 29033965Sjdp long pad_size; /* Stack pad size. */ 29133965Sjdp long current_address; /* Current stack segment address. */ 29233965Sjdp long current_size; /* Current stack segment size. This 29333965Sjdp number is actually corrupted by STKSTAT to 29433965Sjdp include the fifteen word trailer area. */ 29533965Sjdp long initial_address; /* Address of initial segment. */ 29633965Sjdp long initial_size; /* Size of initial segment. */ 29733965Sjdp }; 29833965Sjdp 29933965Sjdp/* The following structure describes the data structure which trails 30033965Sjdp any stack segment. I think that the description in 'asdef' is 30133965Sjdp out of date. I only describe the parts that I am sure about. */ 30233965Sjdp 30333965Sjdpstruct stk_trailer 30433965Sjdp { 30533965Sjdp long this_address; /* Address of this block. */ 30633965Sjdp long this_size; /* Size of this block (does not include 30733965Sjdp this trailer). */ 30833965Sjdp long unknown2; 30933965Sjdp long unknown3; 31033965Sjdp long link; /* Address of trailer block of previous 31133965Sjdp segment. */ 31233965Sjdp long unknown5; 31333965Sjdp long unknown6; 31433965Sjdp long unknown7; 31533965Sjdp long unknown8; 31633965Sjdp long unknown9; 31733965Sjdp long unknown10; 31833965Sjdp long unknown11; 31933965Sjdp long unknown12; 32033965Sjdp long unknown13; 32133965Sjdp long unknown14; 32233965Sjdp }; 32333965Sjdp 32433965Sjdp#endif /* CRAY2 */ 32533965Sjdp#endif /* not CRAY_STACK */ 32633965Sjdp 32733965Sjdp#ifdef CRAY2 32833965Sjdp/* Determine a "stack measure" for an arbitrary ADDRESS. 32933965Sjdp I doubt that "lint" will like this much. */ 33033965Sjdp 33133965Sjdpstatic long 33233965Sjdpi00afunc (long *address) 33333965Sjdp{ 33433965Sjdp struct stk_stat status; 33533965Sjdp struct stk_trailer *trailer; 33633965Sjdp long *block, size; 33733965Sjdp long result = 0; 33833965Sjdp 33933965Sjdp /* We want to iterate through all of the segments. The first 34033965Sjdp step is to get the stack status structure. We could do this 34133965Sjdp more quickly and more directly, perhaps, by referencing the 34233965Sjdp $LM00 common block, but I know that this works. */ 34333965Sjdp 34433965Sjdp STKSTAT (&status); 34533965Sjdp 34633965Sjdp /* Set up the iteration. */ 34733965Sjdp 34833965Sjdp trailer = (struct stk_trailer *) (status.current_address 34933965Sjdp + status.current_size 35033965Sjdp - 15); 35133965Sjdp 35233965Sjdp /* There must be at least one stack segment. Therefore it is 35333965Sjdp a fatal error if "trailer" is null. */ 35433965Sjdp 35533965Sjdp if (trailer == 0) 35633965Sjdp abort (); 35733965Sjdp 35833965Sjdp /* Discard segments that do not contain our argument address. */ 35933965Sjdp 36033965Sjdp while (trailer != 0) 36133965Sjdp { 36233965Sjdp block = (long *) trailer->this_address; 36333965Sjdp size = trailer->this_size; 36433965Sjdp if (block == 0 || size == 0) 36533965Sjdp abort (); 36633965Sjdp trailer = (struct stk_trailer *) trailer->link; 36733965Sjdp if ((block <= address) && (address < (block + size))) 36833965Sjdp break; 36933965Sjdp } 37033965Sjdp 37133965Sjdp /* Set the result to the offset in this segment and add the sizes 37233965Sjdp of all predecessor segments. */ 37333965Sjdp 37433965Sjdp result = address - block; 37533965Sjdp 37633965Sjdp if (trailer == 0) 37733965Sjdp { 37833965Sjdp return result; 37933965Sjdp } 38033965Sjdp 38133965Sjdp do 38233965Sjdp { 38333965Sjdp if (trailer->this_size <= 0) 38433965Sjdp abort (); 38533965Sjdp result += trailer->this_size; 38633965Sjdp trailer = (struct stk_trailer *) trailer->link; 38733965Sjdp } 38833965Sjdp while (trailer != 0); 38933965Sjdp 39033965Sjdp /* We are done. Note that if you present a bogus address (one 39133965Sjdp not in any segment), you will get a different number back, formed 39233965Sjdp from subtracting the address of the first block. This is probably 39333965Sjdp not what you want. */ 39433965Sjdp 39533965Sjdp return (result); 39633965Sjdp} 39733965Sjdp 39833965Sjdp#else /* not CRAY2 */ 39933965Sjdp/* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. 40033965Sjdp Determine the number of the cell within the stack, 40133965Sjdp given the address of the cell. The purpose of this 40233965Sjdp routine is to linearize, in some sense, stack addresses 40333965Sjdp for alloca. */ 40433965Sjdp 40533965Sjdpstatic long 40633965Sjdpi00afunc (long address) 40733965Sjdp{ 40833965Sjdp long stkl = 0; 40933965Sjdp 41033965Sjdp long size, pseg, this_segment, stack; 41133965Sjdp long result = 0; 41233965Sjdp 41333965Sjdp struct stack_segment_linkage *ssptr; 41433965Sjdp 41533965Sjdp /* Register B67 contains the address of the end of the 41633965Sjdp current stack segment. If you (as a subprogram) store 41733965Sjdp your registers on the stack and find that you are past 41833965Sjdp the contents of B67, you have overflowed the segment. 41933965Sjdp 42033965Sjdp B67 also points to the stack segment linkage control 42133965Sjdp area, which is what we are really interested in. */ 42233965Sjdp 42333965Sjdp stkl = CRAY_STACKSEG_END (); 42433965Sjdp ssptr = (struct stack_segment_linkage *) stkl; 42533965Sjdp 42633965Sjdp /* If one subtracts 'size' from the end of the segment, 42733965Sjdp one has the address of the first word of the segment. 42833965Sjdp 42933965Sjdp If this is not the first segment, 'pseg' will be 43033965Sjdp nonzero. */ 43133965Sjdp 43233965Sjdp pseg = ssptr->sspseg; 43333965Sjdp size = ssptr->sssize; 43433965Sjdp 43533965Sjdp this_segment = stkl - size; 43633965Sjdp 43733965Sjdp /* It is possible that calling this routine itself caused 43833965Sjdp a stack overflow. Discard stack segments which do not 43933965Sjdp contain the target address. */ 44033965Sjdp 44133965Sjdp while (!(this_segment <= address && address <= stkl)) 44233965Sjdp { 44333965Sjdp#ifdef DEBUG_I00AFUNC 44433965Sjdp fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); 44533965Sjdp#endif 44633965Sjdp if (pseg == 0) 44733965Sjdp break; 44833965Sjdp stkl = stkl - pseg; 44933965Sjdp ssptr = (struct stack_segment_linkage *) stkl; 45033965Sjdp size = ssptr->sssize; 45133965Sjdp pseg = ssptr->sspseg; 45233965Sjdp this_segment = stkl - size; 45333965Sjdp } 45433965Sjdp 45533965Sjdp result = address - this_segment; 45633965Sjdp 45733965Sjdp /* If you subtract pseg from the current end of the stack, 45833965Sjdp you get the address of the previous stack segment's end. 45933965Sjdp This seems a little convoluted to me, but I'll bet you save 46033965Sjdp a cycle somewhere. */ 46133965Sjdp 46233965Sjdp while (pseg != 0) 46333965Sjdp { 46433965Sjdp#ifdef DEBUG_I00AFUNC 46533965Sjdp fprintf (stderr, "%011o %011o\n", pseg, size); 46633965Sjdp#endif 46733965Sjdp stkl = stkl - pseg; 46833965Sjdp ssptr = (struct stack_segment_linkage *) stkl; 46933965Sjdp size = ssptr->sssize; 47033965Sjdp pseg = ssptr->sspseg; 47133965Sjdp result += size; 47233965Sjdp } 47333965Sjdp return (result); 47433965Sjdp} 47533965Sjdp 47633965Sjdp#endif /* not CRAY2 */ 47733965Sjdp#endif /* CRAY */ 47833965Sjdp 47933965Sjdp#endif /* no alloca */ 480