alloca.c revision 60484
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 2560484Sobrien#include <config.h> 2633965Sjdp#endif 2733965Sjdp 2860484Sobrien#ifdef HAVE_STRING_H 2960484Sobrien#include <string.h> 3060484Sobrien#endif 3160484Sobrien#ifdef HAVE_STDLIB_H 3260484Sobrien#include <stdlib.h> 3360484Sobrien#endif 3460484Sobrien 3560484Sobrien#ifdef emacs 3660484Sobrien#include "blockinput.h" 3760484Sobrien#endif 3860484Sobrien 3960484Sobrien/* If compiling with GCC 2, this file's not needed. Except of course if 4060484Sobrien the C alloca is explicitly requested. */ 4160484Sobrien#if defined (USE_C_ALLOCA) || !defined (__GNUC__) || __GNUC__ < 2 4260484Sobrien 4360484Sobrien/* If someone has defined alloca as a macro, 4460484Sobrien there must be some other way alloca is supposed to work. */ 4533965Sjdp#ifndef alloca 4633965Sjdp 4733965Sjdp#ifdef emacs 4833965Sjdp#ifdef static 4933965Sjdp/* actually, only want this if static is defined as "" 5033965Sjdp -- this is for usg, in which emacs must undefine static 5133965Sjdp in order to make unexec workable 5233965Sjdp */ 5333965Sjdp#ifndef STACK_DIRECTION 5433965Sjdpyou 5533965Sjdplose 5633965Sjdp-- must know STACK_DIRECTION at compile-time 5733965Sjdp#endif /* STACK_DIRECTION undefined */ 5833965Sjdp#endif /* static */ 5933965Sjdp#endif /* emacs */ 6033965Sjdp 6133965Sjdp/* If your stack is a linked list of frames, you have to 6233965Sjdp provide an "address metric" ADDRESS_FUNCTION macro. */ 6333965Sjdp 6433965Sjdp#if defined (CRAY) && defined (CRAY_STACKSEG_END) 6533965Sjdplong i00afunc (); 6633965Sjdp#define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg)) 6733965Sjdp#else 6833965Sjdp#define ADDRESS_FUNCTION(arg) &(arg) 6933965Sjdp#endif 7033965Sjdp 7133965Sjdp#if __STDC__ 7233965Sjdptypedef void *pointer; 7333965Sjdp#else 7433965Sjdptypedef char *pointer; 7533965Sjdp#endif 7633965Sjdp 7733965Sjdp#ifndef NULL 7833965Sjdp#define NULL 0 7933965Sjdp#endif 8033965Sjdp 8133965Sjdp/* Different portions of Emacs need to call different versions of 8233965Sjdp malloc. The Emacs executable needs alloca to call xmalloc, because 8333965Sjdp ordinary malloc isn't protected from input signals. On the other 8433965Sjdp hand, the utilities in lib-src need alloca to call malloc; some of 8533965Sjdp them are very simple, and don't have an xmalloc routine. 8633965Sjdp 8733965Sjdp Non-Emacs programs expect this to call use xmalloc. 8833965Sjdp 8933965Sjdp Callers below should use malloc. */ 9033965Sjdp 9133965Sjdp#ifndef emacs 9233965Sjdp#define malloc xmalloc 9333965Sjdp#endif 9460484Sobrienextern pointer malloc (); 9533965Sjdp 9633965Sjdp/* Define STACK_DIRECTION if you know the direction of stack 9733965Sjdp growth for your system; otherwise it will be automatically 9833965Sjdp deduced at run-time. 9933965Sjdp 10033965Sjdp STACK_DIRECTION > 0 => grows toward higher addresses 10133965Sjdp STACK_DIRECTION < 0 => grows toward lower addresses 10233965Sjdp STACK_DIRECTION = 0 => direction of growth unknown */ 10333965Sjdp 10433965Sjdp#ifndef STACK_DIRECTION 10533965Sjdp#define STACK_DIRECTION 0 /* Direction unknown. */ 10633965Sjdp#endif 10733965Sjdp 10833965Sjdp#if STACK_DIRECTION != 0 10933965Sjdp 11033965Sjdp#define STACK_DIR STACK_DIRECTION /* Known at compile-time. */ 11133965Sjdp 11233965Sjdp#else /* STACK_DIRECTION == 0; need run-time code. */ 11333965Sjdp 11433965Sjdpstatic int stack_dir; /* 1 or -1 once known. */ 11533965Sjdp#define STACK_DIR stack_dir 11633965Sjdp 11733965Sjdpstatic void 11833965Sjdpfind_stack_direction () 11933965Sjdp{ 12033965Sjdp static char *addr = NULL; /* Address of first `dummy', once known. */ 12133965Sjdp auto char dummy; /* To get stack address. */ 12233965Sjdp 12333965Sjdp if (addr == NULL) 12433965Sjdp { /* Initial entry. */ 12533965Sjdp addr = ADDRESS_FUNCTION (dummy); 12633965Sjdp 12733965Sjdp find_stack_direction (); /* Recurse once. */ 12833965Sjdp } 12933965Sjdp else 13033965Sjdp { 13133965Sjdp /* Second entry. */ 13233965Sjdp if (ADDRESS_FUNCTION (dummy) > addr) 13333965Sjdp stack_dir = 1; /* Stack grew upward. */ 13433965Sjdp else 13533965Sjdp stack_dir = -1; /* Stack grew downward. */ 13633965Sjdp } 13733965Sjdp} 13833965Sjdp 13933965Sjdp#endif /* STACK_DIRECTION == 0 */ 14033965Sjdp 14133965Sjdp/* An "alloca header" is used to: 14233965Sjdp (a) chain together all alloca'ed blocks; 14333965Sjdp (b) keep track of stack depth. 14433965Sjdp 14533965Sjdp It is very important that sizeof(header) agree with malloc 14633965Sjdp alignment chunk size. The following default should work okay. */ 14733965Sjdp 14833965Sjdp#ifndef ALIGN_SIZE 14933965Sjdp#define ALIGN_SIZE sizeof(double) 15033965Sjdp#endif 15133965Sjdp 15233965Sjdptypedef union hdr 15333965Sjdp{ 15433965Sjdp char align[ALIGN_SIZE]; /* To force sizeof(header). */ 15533965Sjdp struct 15633965Sjdp { 15733965Sjdp union hdr *next; /* For chaining headers. */ 15833965Sjdp char *deep; /* For stack depth measure. */ 15933965Sjdp } h; 16033965Sjdp} header; 16133965Sjdp 16233965Sjdpstatic header *last_alloca_header = NULL; /* -> last alloca header. */ 16333965Sjdp 16433965Sjdp/* Return a pointer to at least SIZE bytes of storage, 16533965Sjdp which will be automatically reclaimed upon exit from 16633965Sjdp the procedure that called alloca. Originally, this space 16733965Sjdp was supposed to be taken from the current stack frame of the 16833965Sjdp caller, but that method cannot be made to work for some 16933965Sjdp implementations of C, for example under Gould's UTX/32. */ 17033965Sjdp 17133965Sjdppointer 17233965Sjdpalloca (size) 17360484Sobrien unsigned size; 17433965Sjdp{ 17533965Sjdp auto char probe; /* Probes stack depth: */ 17633965Sjdp register char *depth = ADDRESS_FUNCTION (probe); 17733965Sjdp 17833965Sjdp#if STACK_DIRECTION == 0 17933965Sjdp if (STACK_DIR == 0) /* Unknown growth direction. */ 18033965Sjdp find_stack_direction (); 18133965Sjdp#endif 18233965Sjdp 18333965Sjdp /* Reclaim garbage, defined as all alloca'd storage that 18460484Sobrien was allocated from deeper in the stack than currently. */ 18533965Sjdp 18633965Sjdp { 18733965Sjdp register header *hp; /* Traverses linked list. */ 18833965Sjdp 18960484Sobrien#ifdef emacs 19060484Sobrien BLOCK_INPUT; 19160484Sobrien#endif 19260484Sobrien 19333965Sjdp for (hp = last_alloca_header; hp != NULL;) 19433965Sjdp if ((STACK_DIR > 0 && hp->h.deep > depth) 19533965Sjdp || (STACK_DIR < 0 && hp->h.deep < depth)) 19633965Sjdp { 19733965Sjdp register header *np = hp->h.next; 19833965Sjdp 19933965Sjdp free ((pointer) hp); /* Collect garbage. */ 20033965Sjdp 20133965Sjdp hp = np; /* -> next header. */ 20233965Sjdp } 20333965Sjdp else 20433965Sjdp break; /* Rest are not deeper. */ 20533965Sjdp 20633965Sjdp last_alloca_header = hp; /* -> last valid storage. */ 20760484Sobrien 20860484Sobrien#ifdef emacs 20960484Sobrien UNBLOCK_INPUT; 21060484Sobrien#endif 21133965Sjdp } 21233965Sjdp 21333965Sjdp if (size == 0) 21433965Sjdp return NULL; /* No allocation required. */ 21533965Sjdp 21633965Sjdp /* Allocate combined header + user data storage. */ 21733965Sjdp 21833965Sjdp { 21933965Sjdp register pointer new = malloc (sizeof (header) + size); 22033965Sjdp /* Address of header. */ 22133965Sjdp 22260484Sobrien if (new == 0) 22360484Sobrien abort(); 22460484Sobrien 22533965Sjdp ((header *) new)->h.next = last_alloca_header; 22633965Sjdp ((header *) new)->h.deep = depth; 22733965Sjdp 22833965Sjdp last_alloca_header = (header *) new; 22933965Sjdp 23033965Sjdp /* User storage begins just after header. */ 23133965Sjdp 23233965Sjdp return (pointer) ((char *) new + sizeof (header)); 23333965Sjdp } 23433965Sjdp} 23533965Sjdp 23633965Sjdp#if defined (CRAY) && defined (CRAY_STACKSEG_END) 23733965Sjdp 23833965Sjdp#ifdef DEBUG_I00AFUNC 23933965Sjdp#include <stdio.h> 24033965Sjdp#endif 24133965Sjdp 24233965Sjdp#ifndef CRAY_STACK 24333965Sjdp#define CRAY_STACK 24433965Sjdp#ifndef CRAY2 24533965Sjdp/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ 24633965Sjdpstruct stack_control_header 24733965Sjdp { 24833965Sjdp long shgrow:32; /* Number of times stack has grown. */ 24933965Sjdp long shaseg:32; /* Size of increments to stack. */ 25033965Sjdp long shhwm:32; /* High water mark of stack. */ 25133965Sjdp long shsize:32; /* Current size of stack (all segments). */ 25233965Sjdp }; 25333965Sjdp 25433965Sjdp/* The stack segment linkage control information occurs at 25533965Sjdp the high-address end of a stack segment. (The stack 25633965Sjdp grows from low addresses to high addresses.) The initial 25733965Sjdp part of the stack segment linkage control information is 25833965Sjdp 0200 (octal) words. This provides for register storage 25933965Sjdp for the routine which overflows the stack. */ 26033965Sjdp 26133965Sjdpstruct stack_segment_linkage 26233965Sjdp { 26333965Sjdp long ss[0200]; /* 0200 overflow words. */ 26433965Sjdp long sssize:32; /* Number of words in this segment. */ 26533965Sjdp long ssbase:32; /* Offset to stack base. */ 26633965Sjdp long:32; 26733965Sjdp long sspseg:32; /* Offset to linkage control of previous 26833965Sjdp segment of stack. */ 26933965Sjdp long:32; 27033965Sjdp long sstcpt:32; /* Pointer to task common address block. */ 27133965Sjdp long sscsnm; /* Private control structure number for 27233965Sjdp microtasking. */ 27333965Sjdp long ssusr1; /* Reserved for user. */ 27433965Sjdp long ssusr2; /* Reserved for user. */ 27533965Sjdp long sstpid; /* Process ID for pid based multi-tasking. */ 27633965Sjdp long ssgvup; /* Pointer to multitasking thread giveup. */ 27733965Sjdp long sscray[7]; /* Reserved for Cray Research. */ 27833965Sjdp long ssa0; 27933965Sjdp long ssa1; 28033965Sjdp long ssa2; 28133965Sjdp long ssa3; 28233965Sjdp long ssa4; 28333965Sjdp long ssa5; 28433965Sjdp long ssa6; 28533965Sjdp long ssa7; 28633965Sjdp long sss0; 28733965Sjdp long sss1; 28833965Sjdp long sss2; 28933965Sjdp long sss3; 29033965Sjdp long sss4; 29133965Sjdp long sss5; 29233965Sjdp long sss6; 29333965Sjdp long sss7; 29433965Sjdp }; 29533965Sjdp 29633965Sjdp#else /* CRAY2 */ 29733965Sjdp/* The following structure defines the vector of words 29833965Sjdp returned by the STKSTAT library routine. */ 29933965Sjdpstruct stk_stat 30033965Sjdp { 30133965Sjdp long now; /* Current total stack size. */ 30233965Sjdp long maxc; /* Amount of contiguous space which would 30333965Sjdp be required to satisfy the maximum 30433965Sjdp stack demand to date. */ 30533965Sjdp long high_water; /* Stack high-water mark. */ 30633965Sjdp long overflows; /* Number of stack overflow ($STKOFEN) calls. */ 30733965Sjdp long hits; /* Number of internal buffer hits. */ 30833965Sjdp long extends; /* Number of block extensions. */ 30933965Sjdp long stko_mallocs; /* Block allocations by $STKOFEN. */ 31033965Sjdp long underflows; /* Number of stack underflow calls ($STKRETN). */ 31133965Sjdp long stko_free; /* Number of deallocations by $STKRETN. */ 31233965Sjdp long stkm_free; /* Number of deallocations by $STKMRET. */ 31333965Sjdp long segments; /* Current number of stack segments. */ 31433965Sjdp long maxs; /* Maximum number of stack segments so far. */ 31533965Sjdp long pad_size; /* Stack pad size. */ 31633965Sjdp long current_address; /* Current stack segment address. */ 31733965Sjdp long current_size; /* Current stack segment size. This 31833965Sjdp number is actually corrupted by STKSTAT to 31933965Sjdp include the fifteen word trailer area. */ 32033965Sjdp long initial_address; /* Address of initial segment. */ 32133965Sjdp long initial_size; /* Size of initial segment. */ 32233965Sjdp }; 32333965Sjdp 32433965Sjdp/* The following structure describes the data structure which trails 32533965Sjdp any stack segment. I think that the description in 'asdef' is 32633965Sjdp out of date. I only describe the parts that I am sure about. */ 32733965Sjdp 32833965Sjdpstruct stk_trailer 32933965Sjdp { 33033965Sjdp long this_address; /* Address of this block. */ 33133965Sjdp long this_size; /* Size of this block (does not include 33233965Sjdp this trailer). */ 33333965Sjdp long unknown2; 33433965Sjdp long unknown3; 33533965Sjdp long link; /* Address of trailer block of previous 33633965Sjdp segment. */ 33733965Sjdp long unknown5; 33833965Sjdp long unknown6; 33933965Sjdp long unknown7; 34033965Sjdp long unknown8; 34133965Sjdp long unknown9; 34233965Sjdp long unknown10; 34333965Sjdp long unknown11; 34433965Sjdp long unknown12; 34533965Sjdp long unknown13; 34633965Sjdp long unknown14; 34733965Sjdp }; 34833965Sjdp 34933965Sjdp#endif /* CRAY2 */ 35033965Sjdp#endif /* not CRAY_STACK */ 35133965Sjdp 35233965Sjdp#ifdef CRAY2 35333965Sjdp/* Determine a "stack measure" for an arbitrary ADDRESS. 35460484Sobrien I doubt that "lint" will like this much. */ 35533965Sjdp 35633965Sjdpstatic long 35733965Sjdpi00afunc (long *address) 35833965Sjdp{ 35933965Sjdp struct stk_stat status; 36033965Sjdp struct stk_trailer *trailer; 36133965Sjdp long *block, size; 36233965Sjdp long result = 0; 36333965Sjdp 36433965Sjdp /* We want to iterate through all of the segments. The first 36533965Sjdp step is to get the stack status structure. We could do this 36633965Sjdp more quickly and more directly, perhaps, by referencing the 36733965Sjdp $LM00 common block, but I know that this works. */ 36833965Sjdp 36933965Sjdp STKSTAT (&status); 37033965Sjdp 37133965Sjdp /* Set up the iteration. */ 37233965Sjdp 37333965Sjdp trailer = (struct stk_trailer *) (status.current_address 37433965Sjdp + status.current_size 37533965Sjdp - 15); 37633965Sjdp 37733965Sjdp /* There must be at least one stack segment. Therefore it is 37833965Sjdp a fatal error if "trailer" is null. */ 37933965Sjdp 38033965Sjdp if (trailer == 0) 38133965Sjdp abort (); 38233965Sjdp 38333965Sjdp /* Discard segments that do not contain our argument address. */ 38433965Sjdp 38533965Sjdp while (trailer != 0) 38633965Sjdp { 38733965Sjdp block = (long *) trailer->this_address; 38833965Sjdp size = trailer->this_size; 38933965Sjdp if (block == 0 || size == 0) 39033965Sjdp abort (); 39133965Sjdp trailer = (struct stk_trailer *) trailer->link; 39233965Sjdp if ((block <= address) && (address < (block + size))) 39333965Sjdp break; 39433965Sjdp } 39533965Sjdp 39633965Sjdp /* Set the result to the offset in this segment and add the sizes 39733965Sjdp of all predecessor segments. */ 39833965Sjdp 39933965Sjdp result = address - block; 40033965Sjdp 40133965Sjdp if (trailer == 0) 40233965Sjdp { 40333965Sjdp return result; 40433965Sjdp } 40533965Sjdp 40633965Sjdp do 40733965Sjdp { 40833965Sjdp if (trailer->this_size <= 0) 40933965Sjdp abort (); 41033965Sjdp result += trailer->this_size; 41133965Sjdp trailer = (struct stk_trailer *) trailer->link; 41233965Sjdp } 41333965Sjdp while (trailer != 0); 41433965Sjdp 41533965Sjdp /* We are done. Note that if you present a bogus address (one 41633965Sjdp not in any segment), you will get a different number back, formed 41733965Sjdp from subtracting the address of the first block. This is probably 41833965Sjdp not what you want. */ 41933965Sjdp 42033965Sjdp return (result); 42133965Sjdp} 42233965Sjdp 42333965Sjdp#else /* not CRAY2 */ 42433965Sjdp/* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. 42533965Sjdp Determine the number of the cell within the stack, 42633965Sjdp given the address of the cell. The purpose of this 42733965Sjdp routine is to linearize, in some sense, stack addresses 42833965Sjdp for alloca. */ 42933965Sjdp 43033965Sjdpstatic long 43133965Sjdpi00afunc (long address) 43233965Sjdp{ 43333965Sjdp long stkl = 0; 43433965Sjdp 43533965Sjdp long size, pseg, this_segment, stack; 43633965Sjdp long result = 0; 43733965Sjdp 43833965Sjdp struct stack_segment_linkage *ssptr; 43933965Sjdp 44033965Sjdp /* Register B67 contains the address of the end of the 44133965Sjdp current stack segment. If you (as a subprogram) store 44233965Sjdp your registers on the stack and find that you are past 44333965Sjdp the contents of B67, you have overflowed the segment. 44433965Sjdp 44533965Sjdp B67 also points to the stack segment linkage control 44633965Sjdp area, which is what we are really interested in. */ 44733965Sjdp 44833965Sjdp stkl = CRAY_STACKSEG_END (); 44933965Sjdp ssptr = (struct stack_segment_linkage *) stkl; 45033965Sjdp 45133965Sjdp /* If one subtracts 'size' from the end of the segment, 45233965Sjdp one has the address of the first word of the segment. 45333965Sjdp 45433965Sjdp If this is not the first segment, 'pseg' will be 45533965Sjdp nonzero. */ 45633965Sjdp 45733965Sjdp pseg = ssptr->sspseg; 45833965Sjdp size = ssptr->sssize; 45933965Sjdp 46033965Sjdp this_segment = stkl - size; 46133965Sjdp 46233965Sjdp /* It is possible that calling this routine itself caused 46333965Sjdp a stack overflow. Discard stack segments which do not 46433965Sjdp contain the target address. */ 46533965Sjdp 46633965Sjdp while (!(this_segment <= address && address <= stkl)) 46733965Sjdp { 46833965Sjdp#ifdef DEBUG_I00AFUNC 46933965Sjdp fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); 47033965Sjdp#endif 47133965Sjdp if (pseg == 0) 47233965Sjdp break; 47333965Sjdp stkl = stkl - pseg; 47433965Sjdp ssptr = (struct stack_segment_linkage *) stkl; 47533965Sjdp size = ssptr->sssize; 47633965Sjdp pseg = ssptr->sspseg; 47733965Sjdp this_segment = stkl - size; 47833965Sjdp } 47933965Sjdp 48033965Sjdp result = address - this_segment; 48133965Sjdp 48233965Sjdp /* If you subtract pseg from the current end of the stack, 48333965Sjdp you get the address of the previous stack segment's end. 48433965Sjdp This seems a little convoluted to me, but I'll bet you save 48533965Sjdp a cycle somewhere. */ 48633965Sjdp 48733965Sjdp while (pseg != 0) 48833965Sjdp { 48933965Sjdp#ifdef DEBUG_I00AFUNC 49033965Sjdp fprintf (stderr, "%011o %011o\n", pseg, size); 49133965Sjdp#endif 49233965Sjdp stkl = stkl - pseg; 49333965Sjdp ssptr = (struct stack_segment_linkage *) stkl; 49433965Sjdp size = ssptr->sssize; 49533965Sjdp pseg = ssptr->sspseg; 49633965Sjdp result += size; 49733965Sjdp } 49833965Sjdp return (result); 49933965Sjdp} 50033965Sjdp 50133965Sjdp#endif /* not CRAY2 */ 50233965Sjdp#endif /* CRAY */ 50333965Sjdp 50433965Sjdp#endif /* no alloca */ 50560484Sobrien#endif /* not GCC version 2 */ 506