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