e576bb2002-10-11Martin Nilsson /* || This file is part of Pike. For copyright information see COPYRIGHT. || Pike is distributed under GPL, LGPL and MPL. See the file COPYING || for more information.
ab6f442011-04-25Martin Stjernholm || $Id$
e576bb2002-10-11Martin Nilsson */
24ddc71998-03-28Henrik Grubbström (Grubba) 
5267b71995-08-09Fredrik Hübinette (Hubbe) #include <stdio.h> /* alloca -- (mostly) portable public-domain implementation -- D A Gwyn last edit: 86/05/30 rms include config.h, since on VMS it renames some symbols. Use xmalloc instead of malloc. This implementation of the PWB library alloca() function, which is used to allocate space off the run-time stack so that it is automatically reclaimed upon procedure exit, was inspired by discussions with J. Q. Johnson of Cornell. It should work under any C implementation that uses an actual procedure stack (as opposed to a linked list of frames). There are some preprocessor constants that can be defined when compiling for your specific system, for improved efficiency; however, the defaults should be okay. The general concept of this implementation is to keep track of all alloca()-allocated blocks, and reclaim any that are found to be deeper in the stack than the current invocation. This heuristic does not reclaim storage as soon as it becomes invalid, but it will do so eventually. As a special case, alloca(0) reclaims storage without allocating any. It is a good idea to use alloca(0) in your main control loop, etc. to force garbage collection. */ #ifndef lint static char SCCSid[] = "@(#)alloca.c 1.1"; /* for the "what" utility */ #endif #ifdef emacs #include "global.h" #ifdef static /* actually, only want this if static is defined as "" -- this is for usg, in which emacs must undefine static in order to make unexec workable */ #ifndef STACK_DIRECTION you lose -- must know STACK_DIRECTION at compile-time #endif /* STACK_DIRECTION undefined */ #endif /* static */ #endif /* emacs */ #ifdef X3J11 typedef void *pointer; /* generic pointer type */ #else typedef char *pointer; /* generic pointer type */ #endif #ifndef NULL #define NULL 0 /* null pointer constant */ #endif extern void free(); extern pointer malloc(); /* Define STACK_DIRECTION if you know the direction of stack growth for your system; otherwise it will be automatically deduced at run-time. STACK_DIRECTION > 0 => grows toward higher addresses STACK_DIRECTION < 0 => grows toward lower addresses STACK_DIRECTION = 0 => direction of growth unknown */ #ifndef STACK_DIRECTION #define STACK_DIRECTION 0 /* direction unknown */ #endif #if STACK_DIRECTION != 0 #define STACK_DIR STACK_DIRECTION /* known at compile-time */ #else /* STACK_DIRECTION == 0; need run-time code */ static int stack_dir; /* 1 or -1 once known */ #define STACK_DIR stack_dir static void find_stack_direction (/* void */) { static char *addr = NULL; /* address of first `dummy', once known */ auto char dummy; /* to get stack address */ if (addr == NULL) { /* initial entry */ addr = &dummy; find_stack_direction (); /* recurse once */ } else /* second entry */ if (&dummy > addr) stack_dir = 1; /* stack grew upward */ else stack_dir = -1; /* stack grew downward */ } #endif /* STACK_DIRECTION == 0 */ /* An "alloca header" is used to: (a) chain together all alloca()ed blocks; (b) keep track of stack depth. It is very important that sizeof(header) agree with malloc() alignment chunk size. The following default should work okay. */ #ifndef ALIGN_SIZE #define ALIGN_SIZE sizeof(double) #endif typedef union hdr { char align[ALIGN_SIZE]; /* to force sizeof(header) */ struct { union hdr *next; /* for chaining headers */ char *deep; /* for stack depth measure */ } h; } header; /* alloca( size ) returns a pointer to at least `size' bytes of storage which will be automatically reclaimed upon exit from the procedure that called alloca(). Originally, this space
4218011999-01-31Fredrik Hübinette (Hubbe)  was supposed to be taken from the current stack pike_frame of the
5267b71995-08-09Fredrik Hübinette (Hubbe)  caller, but that method cannot be made to work for some implementations of C, for example under Gould's UTX/32. */ static header *last_alloca_header = NULL; /* -> last alloca header */ pointer alloca (size) /* returns pointer to storage */ unsigned size; /* # bytes to allocate */ { auto char probe; /* probes stack depth: */ register char *depth = &probe; #if STACK_DIRECTION == 0 if (STACK_DIR == 0) /* unknown growth direction */ find_stack_direction (); #endif /* Reclaim garbage, defined as all alloca()ed storage that was allocated from deeper in the stack than currently. */ { register header *hp; /* traverses linked list */ for (hp = last_alloca_header; hp != NULL;) if (STACK_DIR > 0 && hp->h.deep > depth || STACK_DIR < 0 && hp->h.deep < depth) { register header *np = hp->h.next; free ((pointer) hp); /* collect garbage */ hp = np; /* -> next header */ } else break; /* rest are not deeper */ last_alloca_header = hp; /* -> last valid storage */ } if (size == 0) return NULL; /* no allocation required */ /* Allocate combined header + user data storage. */ { register pointer new = malloc (sizeof (header) + size); /* address of header */ if (!new) { fprintf(stderr,"alloca: failed!"); return NULL; } ((header *)new)->h.next = last_alloca_header; ((header *)new)->h.deep = depth; last_alloca_header = (header *)new; /* User storage begins just after header. */ return (pointer)((char *)new + sizeof(header)); } }