| 1 | /* alloca.c -- allocate automatically reclaimed memory
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| 2 | (Mostly) portable public-domain implementation -- D A Gwyn
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| 3 |
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| 4 | This implementation of the PWB library alloca function,
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| 5 | which is used to allocate space off the run-time stack so
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| 6 | that it is automatically reclaimed upon procedure exit,
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| 7 | was inspired by discussions with J. Q. Johnson of Cornell.
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| 8 | J.Otto Tennant <jot@cray.com> contributed the Cray support.
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| 9 |
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| 10 | There are some preprocessor constants that can
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| 11 | be defined when compiling for your specific system, for
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| 12 | improved efficiency; however, the defaults should be okay.
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| 13 |
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| 14 | The general concept of this implementation is to keep
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| 15 | track of all alloca-allocated blocks, and reclaim any
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| 16 | that are found to be deeper in the stack than the current
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| 17 | invocation. This heuristic does not reclaim storage as
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| 18 | soon as it becomes invalid, but it will do so eventually.
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| 19 |
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| 20 | As a special case, alloca(0) reclaims storage without
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| 21 | allocating any. It is a good idea to use alloca(0) in
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| 22 | your main control loop, etc. to force garbage collection. */
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| 23 |
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| 24 | #ifdef HAVE_CONFIG_H
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| 25 | # include <config.h>
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| 26 | #endif
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| 27 |
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| 28 | #if HAVE_STRING_H
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| 29 | # include <string.h>
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| 30 | #endif
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| 31 | #if HAVE_STDLIB_H
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| 32 | # include <stdlib.h>
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| 33 | #endif
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| 34 |
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| 35 | #ifdef emacs
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| 36 | # include "blockinput.h"
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| 37 | #endif
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| 38 |
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| 39 | /* If compiling with GCC 2, this file's not needed. */
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| 40 | #if !defined (__GNUC__) || __GNUC__ < 2
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| 41 |
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| 42 | /* If someone has defined alloca as a macro,
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| 43 | there must be some other way alloca is supposed to work. */
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| 44 | # ifndef alloca
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| 45 |
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| 46 | # ifdef emacs
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| 47 | # ifdef static
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| 48 | /* actually, only want this if static is defined as ""
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| 49 | -- this is for usg, in which emacs must undefine static
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| 50 | in order to make unexec workable
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| 51 | */
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| 52 | # ifndef STACK_DIRECTION
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| 53 | you
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| 54 | lose
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| 55 | -- must know STACK_DIRECTION at compile-time
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| 56 | # endif /* STACK_DIRECTION undefined */
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| 57 | # endif /* static */
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| 58 | # endif /* emacs */
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| 59 |
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| 60 | /* If your stack is a linked list of frames, you have to
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| 61 | provide an "address metric" ADDRESS_FUNCTION macro. */
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| 62 |
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| 63 | # if defined (CRAY) && defined (CRAY_STACKSEG_END)
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| 64 | long i00afunc ();
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| 65 | # define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
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| 66 | # else
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| 67 | # define ADDRESS_FUNCTION(arg) &(arg)
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| 68 | # endif
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| 69 |
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| 70 | # if __STDC__
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| 71 | typedef void *pointer;
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| 72 | # else
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| 73 | typedef char *pointer;
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| 74 | # endif
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| 75 |
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| 76 | # ifndef NULL
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| 77 | # define NULL 0
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| 78 | # endif
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| 79 |
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| 80 | /* Different portions of Emacs need to call different versions of
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| 81 | malloc. The Emacs executable needs alloca to call xmalloc, because
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| 82 | ordinary malloc isn't protected from input signals. On the other
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| 83 | hand, the utilities in lib-src need alloca to call malloc; some of
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| 84 | them are very simple, and don't have an xmalloc routine.
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| 85 |
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| 86 | Non-Emacs programs expect this to call xmalloc.
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| 87 |
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| 88 | Callers below should use malloc. */
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| 89 |
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| 90 | # ifndef emacs
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| 91 | # undef malloc
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| 92 | # define malloc xmalloc
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| 93 | # endif
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| 94 | extern pointer malloc ();
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| 95 |
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| 96 | /* Define STACK_DIRECTION if you know the direction of stack
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| 97 | growth for your system; otherwise it will be automatically
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| 98 | deduced at run-time.
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| 99 |
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| 100 | STACK_DIRECTION > 0 => grows toward higher addresses
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| 101 | STACK_DIRECTION < 0 => grows toward lower addresses
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| 102 | STACK_DIRECTION = 0 => direction of growth unknown */
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| 103 |
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| 104 | # ifndef STACK_DIRECTION
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| 105 | # define STACK_DIRECTION 0 /* Direction unknown. */
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| 106 | # endif
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| 107 |
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| 108 | # if STACK_DIRECTION != 0
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| 109 |
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| 110 | # define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
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| 111 |
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| 112 | # else /* STACK_DIRECTION == 0; need run-time code. */
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| 113 |
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| 114 | static int stack_dir; /* 1 or -1 once known. */
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| 115 | # define STACK_DIR stack_dir
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| 116 |
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| 117 | static void
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| 118 | find_stack_direction ()
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| 119 | {
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| 120 | static char *addr = NULL; /* Address of first `dummy', once known. */
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| 121 | auto char dummy; /* To get stack address. */
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| 122 |
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| 123 | if (addr == NULL)
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| 124 | { /* Initial entry. */
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| 125 | addr = ADDRESS_FUNCTION (dummy);
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| 126 |
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| 127 | find_stack_direction (); /* Recurse once. */
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| 128 | }
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| 129 | else
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| 130 | {
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| 131 | /* Second entry. */
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| 132 | if (ADDRESS_FUNCTION (dummy) > addr)
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| 133 | stack_dir = 1; /* Stack grew upward. */
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| 134 | else
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| 135 | stack_dir = -1; /* Stack grew downward. */
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| 136 | }
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| 137 | }
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| 138 |
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| 139 | # endif /* STACK_DIRECTION == 0 */
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| 140 |
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| 141 | /* An "alloca header" is used to:
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| 142 | (a) chain together all alloca'ed blocks;
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| 143 | (b) keep track of stack depth.
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| 144 |
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| 145 | It is very important that sizeof(header) agree with malloc
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| 146 | alignment chunk size. The following default should work okay. */
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| 147 |
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| 148 | # ifndef ALIGN_SIZE
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| 149 | # define ALIGN_SIZE sizeof(double)
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| 150 | # endif
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| 151 |
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| 152 | typedef union hdr
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| 153 | {
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| 154 | char align[ALIGN_SIZE]; /* To force sizeof(header). */
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| 155 | struct
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| 156 | {
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| 157 | union hdr *next; /* For chaining headers. */
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| 158 | char *deep; /* For stack depth measure. */
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| 159 | } h;
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| 160 | } header;
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| 161 |
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| 162 | static header *last_alloca_header = NULL; /* -> last alloca header. */
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| 163 |
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| 164 | /* Return a pointer to at least SIZE bytes of storage,
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| 165 | which will be automatically reclaimed upon exit from
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| 166 | the procedure that called alloca. Originally, this space
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| 167 | was supposed to be taken from the current stack frame of the
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| 168 | caller, but that method cannot be made to work for some
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| 169 | implementations of C, for example under Gould's UTX/32. */
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| 170 |
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| 171 | pointer
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| 172 | alloca (size_t size)
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| 173 | {
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| 174 | auto char probe; /* Probes stack depth: */
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| 175 | register char *depth = ADDRESS_FUNCTION (probe);
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| 176 |
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| 177 | # if STACK_DIRECTION == 0
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| 178 | if (STACK_DIR == 0) /* Unknown growth direction. */
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| 179 | find_stack_direction ();
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| 180 | # endif
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| 181 |
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| 182 | /* Reclaim garbage, defined as all alloca'd storage that
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| 183 | was allocated from deeper in the stack than currently. */
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| 184 |
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| 185 | {
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| 186 | register header *hp; /* Traverses linked list. */
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| 187 |
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| 188 | # ifdef emacs
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| 189 | BLOCK_INPUT;
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| 190 | # endif
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| 191 |
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| 192 | for (hp = last_alloca_header; hp != NULL;)
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| 193 | if ((STACK_DIR > 0 && hp->h.deep > depth)
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| 194 | || (STACK_DIR < 0 && hp->h.deep < depth))
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| 195 | {
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| 196 | register header *np = hp->h.next;
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| 197 |
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| 198 | free ((pointer) hp); /* Collect garbage. */
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| 199 |
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| 200 | hp = np; /* -> next header. */
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| 201 | }
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| 202 | else
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| 203 | break; /* Rest are not deeper. */
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| 204 |
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| 205 | last_alloca_header = hp; /* -> last valid storage. */
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| 206 |
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| 207 | # ifdef emacs
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| 208 | UNBLOCK_INPUT;
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| 209 | # endif
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| 210 | }
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| 211 |
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| 212 | if (size == 0)
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| 213 | return NULL; /* No allocation required. */
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| 214 |
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| 215 | /* Allocate combined header + user data storage. */
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| 216 |
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| 217 | {
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| 218 | register pointer new = malloc (sizeof (header) + size);
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| 219 | /* Address of header. */
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| 220 |
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| 221 | if (new == 0)
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| 222 | abort();
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| 223 |
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| 224 | ((header *) new)->h.next = last_alloca_header;
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| 225 | ((header *) new)->h.deep = depth;
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| 226 |
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| 227 | last_alloca_header = (header *) new;
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| 228 |
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| 229 | /* User storage begins just after header. */
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| 230 |
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| 231 | return (pointer) ((char *) new + sizeof (header));
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| 232 | }
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| 233 | }
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| 234 |
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| 235 | # if defined (CRAY) && defined (CRAY_STACKSEG_END)
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| 236 |
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| 237 | # ifdef DEBUG_I00AFUNC
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| 238 | # include <stdio.h>
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| 239 | # endif
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| 240 |
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| 241 | # ifndef CRAY_STACK
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| 242 | # define CRAY_STACK
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| 243 | # ifndef CRAY2
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| 244 | /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
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| 245 | struct stack_control_header
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| 246 | {
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| 247 | long shgrow:32; /* Number of times stack has grown. */
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| 248 | long shaseg:32; /* Size of increments to stack. */
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| 249 | long shhwm:32; /* High water mark of stack. */
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| 250 | long shsize:32; /* Current size of stack (all segments). */
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| 251 | };
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| 252 |
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| 253 | /* The stack segment linkage control information occurs at
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| 254 | the high-address end of a stack segment. (The stack
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| 255 | grows from low addresses to high addresses.) The initial
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| 256 | part of the stack segment linkage control information is
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| 257 | 0200 (octal) words. This provides for register storage
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| 258 | for the routine which overflows the stack. */
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| 259 |
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| 260 | struct stack_segment_linkage
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| 261 | {
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| 262 | long ss[0200]; /* 0200 overflow words. */
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| 263 | long sssize:32; /* Number of words in this segment. */
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| 264 | long ssbase:32; /* Offset to stack base. */
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| 265 | long:32;
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| 266 | long sspseg:32; /* Offset to linkage control of previous
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| 267 | segment of stack. */
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| 268 | long:32;
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| 269 | long sstcpt:32; /* Pointer to task common address block. */
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| 270 | long sscsnm; /* Private control structure number for
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| 271 | microtasking. */
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| 272 | long ssusr1; /* Reserved for user. */
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| 273 | long ssusr2; /* Reserved for user. */
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| 274 | long sstpid; /* Process ID for pid based multi-tasking. */
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| 275 | long ssgvup; /* Pointer to multitasking thread giveup. */
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| 276 | long sscray[7]; /* Reserved for Cray Research. */
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| 277 | long ssa0;
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| 278 | long ssa1;
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| 279 | long ssa2;
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| 280 | long ssa3;
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| 281 | long ssa4;
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| 282 | long ssa5;
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| 283 | long ssa6;
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| 284 | long ssa7;
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| 285 | long sss0;
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| 286 | long sss1;
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| 287 | long sss2;
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| 288 | long sss3;
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| 289 | long sss4;
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| 290 | long sss5;
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| 291 | long sss6;
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| 292 | long sss7;
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| 293 | };
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| 294 |
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| 295 | # else /* CRAY2 */
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| 296 | /* The following structure defines the vector of words
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| 297 | returned by the STKSTAT library routine. */
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| 298 | struct stk_stat
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| 299 | {
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| 300 | long now; /* Current total stack size. */
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| 301 | long maxc; /* Amount of contiguous space which would
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| 302 | be required to satisfy the maximum
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| 303 | stack demand to date. */
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| 304 | long high_water; /* Stack high-water mark. */
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| 305 | long overflows; /* Number of stack overflow ($STKOFEN) calls. */
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| 306 | long hits; /* Number of internal buffer hits. */
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| 307 | long extends; /* Number of block extensions. */
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| 308 | long stko_mallocs; /* Block allocations by $STKOFEN. */
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| 309 | long underflows; /* Number of stack underflow calls ($STKRETN). */
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| 310 | long stko_free; /* Number of deallocations by $STKRETN. */
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| 311 | long stkm_free; /* Number of deallocations by $STKMRET. */
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| 312 | long segments; /* Current number of stack segments. */
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| 313 | long maxs; /* Maximum number of stack segments so far. */
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| 314 | long pad_size; /* Stack pad size. */
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| 315 | long current_address; /* Current stack segment address. */
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| 316 | long current_size; /* Current stack segment size. This
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| 317 | number is actually corrupted by STKSTAT to
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| 318 | include the fifteen word trailer area. */
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| 319 | long initial_address; /* Address of initial segment. */
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| 320 | long initial_size; /* Size of initial segment. */
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| 321 | };
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| 322 |
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| 323 | /* The following structure describes the data structure which trails
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| 324 | any stack segment. I think that the description in 'asdef' is
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| 325 | out of date. I only describe the parts that I am sure about. */
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| 326 |
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| 327 | struct stk_trailer
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| 328 | {
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| 329 | long this_address; /* Address of this block. */
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| 330 | long this_size; /* Size of this block (does not include
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| 331 | this trailer). */
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| 332 | long unknown2;
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| 333 | long unknown3;
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| 334 | long link; /* Address of trailer block of previous
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| 335 | segment. */
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| 336 | long unknown5;
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| 337 | long unknown6;
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| 338 | long unknown7;
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| 339 | long unknown8;
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| 340 | long unknown9;
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| 341 | long unknown10;
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| 342 | long unknown11;
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| 343 | long unknown12;
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| 344 | long unknown13;
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| 345 | long unknown14;
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| 346 | };
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| 347 |
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| 348 | # endif /* CRAY2 */
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| 349 | # endif /* not CRAY_STACK */
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| 350 |
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| 351 | # ifdef CRAY2
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| 352 | /* Determine a "stack measure" for an arbitrary ADDRESS.
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| 353 | I doubt that "lint" will like this much. */
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| 354 |
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| 355 | static long
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| 356 | i00afunc (long *address)
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| 357 | {
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| 358 | struct stk_stat status;
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| 359 | struct stk_trailer *trailer;
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| 360 | long *block, size;
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| 361 | long result = 0;
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| 362 |
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| 363 | /* We want to iterate through all of the segments. The first
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| 364 | step is to get the stack status structure. We could do this
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| 365 | more quickly and more directly, perhaps, by referencing the
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| 366 | $LM00 common block, but I know that this works. */
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| 367 |
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| 368 | STKSTAT (&status);
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| 369 |
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| 370 | /* Set up the iteration. */
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| 371 |
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| 372 | trailer = (struct stk_trailer *) (status.current_address
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| 373 | + status.current_size
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| 374 | - 15);
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| 375 |
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| 376 | /* There must be at least one stack segment. Therefore it is
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| 377 | a fatal error if "trailer" is null. */
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| 378 |
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| 379 | if (trailer == 0)
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| 380 | abort ();
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| 381 |
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| 382 | /* Discard segments that do not contain our argument address. */
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| 383 |
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| 384 | while (trailer != 0)
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| 385 | {
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| 386 | block = (long *) trailer->this_address;
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| 387 | size = trailer->this_size;
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| 388 | if (block == 0 || size == 0)
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| 389 | abort ();
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| 390 | trailer = (struct stk_trailer *) trailer->link;
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| 391 | if ((block <= address) && (address < (block + size)))
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| 392 | break;
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| 393 | }
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| 394 |
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| 395 | /* Set the result to the offset in this segment and add the sizes
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| 396 | of all predecessor segments. */
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| 397 |
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| 398 | result = address - block;
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| 399 |
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| 400 | if (trailer == 0)
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| 401 | {
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| 402 | return result;
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| 403 | }
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| 404 |
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| 405 | do
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| 406 | {
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| 407 | if (trailer->this_size <= 0)
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| 408 | abort ();
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| 409 | result += trailer->this_size;
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| 410 | trailer = (struct stk_trailer *) trailer->link;
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| 411 | }
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| 412 | while (trailer != 0);
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| 413 |
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| 414 | /* We are done. Note that if you present a bogus address (one
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| 415 | not in any segment), you will get a different number back, formed
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| 416 | from subtracting the address of the first block. This is probably
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| 417 | not what you want. */
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| 418 |
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| 419 | return (result);
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| 420 | }
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| 421 |
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| 422 | # else /* not CRAY2 */
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| 423 | /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
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| 424 | Determine the number of the cell within the stack,
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| 425 | given the address of the cell. The purpose of this
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| 426 | routine is to linearize, in some sense, stack addresses
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| 427 | for alloca. */
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| 428 |
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| 429 | static long
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| 430 | i00afunc (long address)
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| 431 | {
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| 432 | long stkl = 0;
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| 433 |
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| 434 | long size, pseg, this_segment, stack;
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| 435 | long result = 0;
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| 436 |
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| 437 | struct stack_segment_linkage *ssptr;
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| 438 |
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| 439 | /* Register B67 contains the address of the end of the
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| 440 | current stack segment. If you (as a subprogram) store
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| 441 | your registers on the stack and find that you are past
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| 442 | the contents of B67, you have overflowed the segment.
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| 443 |
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| 444 | B67 also points to the stack segment linkage control
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| 445 | area, which is what we are really interested in. */
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| 446 |
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| 447 | stkl = CRAY_STACKSEG_END ();
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| 448 | ssptr = (struct stack_segment_linkage *) stkl;
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| 449 |
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| 450 | /* If one subtracts 'size' from the end of the segment,
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| 451 | one has the address of the first word of the segment.
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| 452 |
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| 453 | If this is not the first segment, 'pseg' will be
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| 454 | nonzero. */
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| 455 |
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| 456 | pseg = ssptr->sspseg;
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| 457 | size = ssptr->sssize;
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| 458 |
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| 459 | this_segment = stkl - size;
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| 460 |
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| 461 | /* It is possible that calling this routine itself caused
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| 462 | a stack overflow. Discard stack segments which do not
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|---|
| 463 | contain the target address. */
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| 464 |
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| 465 | while (!(this_segment <= address && address <= stkl))
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| 466 | {
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|---|
| 467 | # ifdef DEBUG_I00AFUNC
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| 468 | fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
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| 469 | # endif
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| 470 | if (pseg == 0)
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| 471 | break;
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| 472 | stkl = stkl - pseg;
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|---|
| 473 | ssptr = (struct stack_segment_linkage *) stkl;
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| 474 | size = ssptr->sssize;
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| 475 | pseg = ssptr->sspseg;
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|---|
| 476 | this_segment = stkl - size;
|
|---|
| 477 | }
|
|---|
| 478 |
|
|---|
| 479 | result = address - this_segment;
|
|---|
| 480 |
|
|---|
| 481 | /* If you subtract pseg from the current end of the stack,
|
|---|
| 482 | you get the address of the previous stack segment's end.
|
|---|
| 483 | This seems a little convoluted to me, but I'll bet you save
|
|---|
| 484 | a cycle somewhere. */
|
|---|
| 485 |
|
|---|
| 486 | while (pseg != 0)
|
|---|
| 487 | {
|
|---|
| 488 | # ifdef DEBUG_I00AFUNC
|
|---|
| 489 | fprintf (stderr, "%011o %011o\n", pseg, size);
|
|---|
| 490 | # endif
|
|---|
| 491 | stkl = stkl - pseg;
|
|---|
| 492 | ssptr = (struct stack_segment_linkage *) stkl;
|
|---|
| 493 | size = ssptr->sssize;
|
|---|
| 494 | pseg = ssptr->sspseg;
|
|---|
| 495 | result += size;
|
|---|
| 496 | }
|
|---|
| 497 | return (result);
|
|---|
| 498 | }
|
|---|
| 499 |
|
|---|
| 500 | # endif /* not CRAY2 */
|
|---|
| 501 | # endif /* CRAY */
|
|---|
| 502 |
|
|---|
| 503 | # endif /* no alloca */
|
|---|
| 504 | #endif /* not GCC version 2 */
|
|---|
