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alloca.c (14234B)
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1 /* alloca.c -- allocate automatically reclaimed memory
2 (Mostly) portable public-domain implementation -- D A Gwyn
3
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.
9
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.
13
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.
19
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. */
23
24 #ifdef HAVE_CONFIG_H
25 #include <config.h>
26 #endif
27
28 #ifdef HAVE_STRING_H
29 #include <string.h>
30 #endif
31 #ifdef HAVE_STDLIB_H
32 #include <stdlib.h>
33 #endif
34
35 #ifdef emacs
36 #include "blockinput.h"
37 #endif
38
39 /* If compiling with GCC 2, this file's not needed. */
40 #if !defined (__GNUC__) || __GNUC__ < 2
41
42 /* If someone has defined alloca as a macro,
43 there must be some other way alloca is supposed to work. */
44 #ifndef alloca
45
46 #ifdef emacs
47 #ifdef static
48 /* actually, only want this if static is defined as ""
49 -- this is for usg, in which emacs must undefine static
50 in order to make unexec workable
51 */
52 #ifndef STACK_DIRECTION
53 you
54 lose
55 -- must know STACK_DIRECTION at compile-time
56 #endif /* STACK_DIRECTION undefined */
57 #endif /* static */
58 #endif /* emacs */
59
60 /* If your stack is a linked list of frames, you have to
61 provide an "address metric" ADDRESS_FUNCTION macro. */
62
63 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
64 long i00afunc ();
65 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
66 #else
67 #define ADDRESS_FUNCTION(arg) &(arg)
68 #endif
69
70 #if __STDC__
71 typedef void *pointer;
72 #else
73 typedef char *pointer;
74 #endif
75
76 #ifndef NULL
77 #define NULL 0
78 #endif
79
80 /* Different portions of Emacs need to call different versions of
81 malloc. The Emacs executable needs alloca to call xmalloc, because
82 ordinary malloc isn't protected from input signals. On the other
83 hand, the utilities in lib-src need alloca to call malloc; some of
84 them are very simple, and don't have an xmalloc routine.
85
86 Non-Emacs programs expect this to call xmalloc.
87
88 Callers below should use malloc. */
89
90 #ifndef emacs
91 #define malloc xmalloc
92 #endif
93 extern pointer malloc ();
94
95 /* Define STACK_DIRECTION if you know the direction of stack
96 growth for your system; otherwise it will be automatically
97 deduced at run-time.
98
99 STACK_DIRECTION > 0 => grows toward higher addresses
100 STACK_DIRECTION < 0 => grows toward lower addresses
101 STACK_DIRECTION = 0 => direction of growth unknown */
102
103 #ifndef STACK_DIRECTION
104 #define STACK_DIRECTION 0 /* Direction unknown. */
105 #endif
106
107 #if STACK_DIRECTION != 0
108
109 #define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
110
111 #else /* STACK_DIRECTION == 0; need run-time code. */
112
113 static int stack_dir; /* 1 or -1 once known. */
114 #define STACK_DIR stack_dir
115
116 static void
117 find_stack_direction ()
118 {
119 static char *addr = NULL; /* Address of first `dummy', once known. */
120 auto char dummy; /* To get stack address. */
121
122 if (addr == NULL)
123 { /* Initial entry. */
124 addr = ADDRESS_FUNCTION (dummy);
125
126 find_stack_direction (); /* Recurse once. */
127 }
128 else
129 {
130 /* Second entry. */
131 if (ADDRESS_FUNCTION (dummy) > addr)
132 stack_dir = 1; /* Stack grew upward. */
133 else
134 stack_dir = -1; /* Stack grew downward. */
135 }
136 }
137
138 #endif /* STACK_DIRECTION == 0 */
139
140 /* An "alloca header" is used to:
141 (a) chain together all alloca'ed blocks;
142 (b) keep track of stack depth.
143
144 It is very important that sizeof(header) agree with malloc
145 alignment chunk size. The following default should work okay. */
146
147 #ifndef ALIGN_SIZE
148 #define ALIGN_SIZE sizeof(double)
149 #endif
150
151 typedef union hdr
152 {
153 char align[ALIGN_SIZE]; /* To force sizeof(header). */
154 struct
155 {
156 union hdr *next; /* For chaining headers. */
157 char *deep; /* For stack depth measure. */
158 } h;
159 } header;
160
161 static header *last_alloca_header = NULL; /* -> last alloca header. */
162
163 /* Return a pointer to at least SIZE bytes of storage,
164 which will be automatically reclaimed upon exit from
165 the procedure that called alloca. Originally, this space
166 was supposed to be taken from the current stack frame of the
167 caller, but that method cannot be made to work for some
168 implementations of C, for example under Gould's UTX/32. */
169
170 pointer
171 alloca (size)
172 unsigned size;
173 {
174 auto char probe; /* Probes stack depth: */
175 register char *depth = ADDRESS_FUNCTION (probe);
176
177 #if STACK_DIRECTION == 0
178 if (STACK_DIR == 0) /* Unknown growth direction. */
179 find_stack_direction ();
180 #endif
181
182 /* Reclaim garbage, defined as all alloca'd storage that
183 was allocated from deeper in the stack than currently. */
184
185 {
186 register header *hp; /* Traverses linked list. */
187
188 #ifdef emacs
189 BLOCK_INPUT;
190 #endif
191
192 for (hp = last_alloca_header; hp != NULL;)
193 if ((STACK_DIR > 0 && hp->h.deep > depth)
194 || (STACK_DIR < 0 && hp->h.deep < depth))
195 {
196 register header *np = hp->h.next;
197
198 free ((pointer) hp); /* Collect garbage. */
199
200 hp = np; /* -> next header. */
201 }
202 else
203 break; /* Rest are not deeper. */
204
205 last_alloca_header = hp; /* -> last valid storage. */
206
207 #ifdef emacs
208 UNBLOCK_INPUT;
209 #endif
210 }
211
212 if (size == 0)
213 return NULL; /* No allocation required. */
214
215 /* Allocate combined header + user data storage. */
216
217 {
218 register pointer new = malloc (sizeof (header) + size);
219 /* Address of header. */
220
221 if (new == 0)
222 abort();
223
224 ((header *) new)->h.next = last_alloca_header;
225 ((header *) new)->h.deep = depth;
226
227 last_alloca_header = (header *) new;
228
229 /* User storage begins just after header. */
230
231 return (pointer) ((char *) new + sizeof (header));
232 }
233 }
234
235 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
236
237 #ifdef DEBUG_I00AFUNC
238 #include <stdio.h>
239 #endif
240
241 #ifndef CRAY_STACK
242 #define CRAY_STACK
243 #ifndef CRAY2
244 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
245 struct stack_control_header
246 {
247 long shgrow:32; /* Number of times stack has grown. */
248 long shaseg:32; /* Size of increments to stack. */
249 long shhwm:32; /* High water mark of stack. */
250 long shsize:32; /* Current size of stack (all segments). */
251 };
252
253 /* The stack segment linkage control information occurs at
254 the high-address end of a stack segment. (The stack
255 grows from low addresses to high addresses.) The initial
256 part of the stack segment linkage control information is
257 0200 (octal) words. This provides for register storage
258 for the routine which overflows the stack. */
259
260 struct stack_segment_linkage
261 {
262 long ss[0200]; /* 0200 overflow words. */
263 long sssize:32; /* Number of words in this segment. */
264 long ssbase:32; /* Offset to stack base. */
265 long:32;
266 long sspseg:32; /* Offset to linkage control of previous
267 segment of stack. */
268 long:32;
269 long sstcpt:32; /* Pointer to task common address block. */
270 long sscsnm; /* Private control structure number for
271 microtasking. */
272 long ssusr1; /* Reserved for user. */
273 long ssusr2; /* Reserved for user. */
274 long sstpid; /* Process ID for pid based multi-tasking. */
275 long ssgvup; /* Pointer to multitasking thread giveup. */
276 long sscray[7]; /* Reserved for Cray Research. */
277 long ssa0;
278 long ssa1;
279 long ssa2;
280 long ssa3;
281 long ssa4;
282 long ssa5;
283 long ssa6;
284 long ssa7;
285 long sss0;
286 long sss1;
287 long sss2;
288 long sss3;
289 long sss4;
290 long sss5;
291 long sss6;
292 long sss7;
293 };
294
295 #else /* CRAY2 */
296 /* The following structure defines the vector of words
297 returned by the STKSTAT library routine. */
298 struct stk_stat
299 {
300 long now; /* Current total stack size. */
301 long maxc; /* Amount of contiguous space which would
302 be required to satisfy the maximum
303 stack demand to date. */
304 long high_water; /* Stack high-water mark. */
305 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
306 long hits; /* Number of internal buffer hits. */
307 long extends; /* Number of block extensions. */
308 long stko_mallocs; /* Block allocations by $STKOFEN. */
309 long underflows; /* Number of stack underflow calls ($STKRETN). */
310 long stko_free; /* Number of deallocations by $STKRETN. */
311 long stkm_free; /* Number of deallocations by $STKMRET. */
312 long segments; /* Current number of stack segments. */
313 long maxs; /* Maximum number of stack segments so far. */
314 long pad_size; /* Stack pad size. */
315 long current_address; /* Current stack segment address. */
316 long current_size; /* Current stack segment size. This
317 number is actually corrupted by STKSTAT to
318 include the fifteen word trailer area. */
319 long initial_address; /* Address of initial segment. */
320 long initial_size; /* Size of initial segment. */
321 };
322
323 /* The following structure describes the data structure which trails
324 any stack segment. I think that the description in 'asdef' is
325 out of date. I only describe the parts that I am sure about. */
326
327 struct stk_trailer
328 {
329 long this_address; /* Address of this block. */
330 long this_size; /* Size of this block (does not include
331 this trailer). */
332 long unknown2;
333 long unknown3;
334 long link; /* Address of trailer block of previous
335 segment. */
336 long unknown5;
337 long unknown6;
338 long unknown7;
339 long unknown8;
340 long unknown9;
341 long unknown10;
342 long unknown11;
343 long unknown12;
344 long unknown13;
345 long unknown14;
346 };
347
348 #endif /* CRAY2 */
349 #endif /* not CRAY_STACK */
350
351 #ifdef CRAY2
352 /* Determine a "stack measure" for an arbitrary ADDRESS.
353 I doubt that "lint" will like this much. */
354
355 static long
356 i00afunc (long *address)
357 {
358 struct stk_stat status;
359 struct stk_trailer *trailer;
360 long *block, size;
361 long result = 0;
362
363 /* We want to iterate through all of the segments. The first
364 step is to get the stack status structure. We could do this
365 more quickly and more directly, perhaps, by referencing the
366 $LM00 common block, but I know that this works. */
367
368 STKSTAT (&status);
369
370 /* Set up the iteration. */
371
372 trailer = (struct stk_trailer *) (status.current_address
373 + status.current_size
374 - 15);
375
376 /* There must be at least one stack segment. Therefore it is
377 a fatal error if "trailer" is null. */
378
379 if (trailer == 0)
380 abort ();
381
382 /* Discard segments that do not contain our argument address. */
383
384 while (trailer != 0)
385 {
386 block = (long *) trailer->this_address;
387 size = trailer->this_size;
388 if (block == 0 || size == 0)
389 abort ();
390 trailer = (struct stk_trailer *) trailer->link;
391 if ((block <= address) && (address < (block + size)))
392 break;
393 }
394
395 /* Set the result to the offset in this segment and add the sizes
396 of all predecessor segments. */
397
398 result = address - block;
399
400 if (trailer == 0)
401 {
402 return result;
403 }
404
405 do
406 {
407 if (trailer->this_size <= 0)
408 abort ();
409 result += trailer->this_size;
410 trailer = (struct stk_trailer *) trailer->link;
411 }
412 while (trailer != 0);
413
414 /* We are done. Note that if you present a bogus address (one
415 not in any segment), you will get a different number back, formed
416 from subtracting the address of the first block. This is probably
417 not what you want. */
418
419 return (result);
420 }
421
422 #else /* not CRAY2 */
423 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
424 Determine the number of the cell within the stack,
425 given the address of the cell. The purpose of this
426 routine is to linearize, in some sense, stack addresses
427 for alloca. */
428
429 static long
430 i00afunc (long address)
431 {
432 long stkl = 0;
433
434 long size, pseg, this_segment, stack;
435 long result = 0;
436
437 struct stack_segment_linkage *ssptr;
438
439 /* Register B67 contains the address of the end of the
440 current stack segment. If you (as a subprogram) store
441 your registers on the stack and find that you are past
442 the contents of B67, you have overflowed the segment.
443
444 B67 also points to the stack segment linkage control
445 area, which is what we are really interested in. */
446
447 stkl = CRAY_STACKSEG_END ();
448 ssptr = (struct stack_segment_linkage *) stkl;
449
450 /* If one subtracts 'size' from the end of the segment,
451 one has the address of the first word of the segment.
452
453 If this is not the first segment, 'pseg' will be
454 nonzero. */
455
456 pseg = ssptr->sspseg;
457 size = ssptr->sssize;
458
459 this_segment = stkl - size;
460
461 /* It is possible that calling this routine itself caused
462 a stack overflow. Discard stack segments which do not
463 contain the target address. */
464
465 while (!(this_segment <= address && address <= stkl))
466 {
467 #ifdef DEBUG_I00AFUNC
468 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
469 #endif
470 if (pseg == 0)
471 break;
472 stkl = stkl - pseg;
473 ssptr = (struct stack_segment_linkage *) stkl;
474 size = ssptr->sssize;
475 pseg = ssptr->sspseg;
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 */