Mercurial > hg-old > index.cgi

comparison lib/alloca.c @ 398:7987ee447833 3.0-beta1

Find changesets by keywords (author, files, the commit message), revision number or hash, or revset expression.
Added generated files for release
author lost@l-w.ca
date Fri, 23 Jul 2010 17:18:52 -0600
parents
children
comparison
equal deleted inserted replaced
397:09fe7c40a082 398:7987ee447833
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 #include <config.h>
25
26 #include <alloca.h>
27
28 #include <string.h>
29 #include <stdlib.h>
30
31 #ifdef emacs
32 # include "lisp.h"
33 # include "blockinput.h"
34 # ifdef EMACS_FREE
35 # undef free
36 # define free EMACS_FREE
37 # endif
38 #else
39 # define memory_full() abort ()
40 #endif
41
42 /* If compiling with GCC 2, this file's not needed. */
43 #if !defined (__GNUC__) || __GNUC__ < 2
44
45 /* If someone has defined alloca as a macro,
46 there must be some other way alloca is supposed to work. */
47 # ifndef alloca
48
49 # ifdef emacs
50 # ifdef static
51 /* actually, only want this if static is defined as ""
52 -- this is for usg, in which emacs must undefine static
53 in order to make unexec workable
54 */
55 # ifndef STACK_DIRECTION
56 you
57 lose
58 -- must know STACK_DIRECTION at compile-time
59 /* Using #error here is not wise since this file should work for
60 old and obscure compilers. */
61 # endif /* STACK_DIRECTION undefined */
62 # endif /* static */
63 # endif /* emacs */
64
65 /* If your stack is a linked list of frames, you have to
66 provide an "address metric" ADDRESS_FUNCTION macro. */
67
68 # if defined (CRAY) && defined (CRAY_STACKSEG_END)
69 long i00afunc ();
70 # define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
71 # else
72 # define ADDRESS_FUNCTION(arg) &(arg)
73 # endif
74
75 /* Define STACK_DIRECTION if you know the direction of stack
76 growth for your system; otherwise it will be automatically
77 deduced at run-time.
78
79 STACK_DIRECTION > 0 => grows toward higher addresses
80 STACK_DIRECTION < 0 => grows toward lower addresses
81 STACK_DIRECTION = 0 => direction of growth unknown */
82
83 # ifndef STACK_DIRECTION
84 # define STACK_DIRECTION 0 /* Direction unknown. */
85 # endif
86
87 # if STACK_DIRECTION != 0
88
89 # define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
90
91 # else /* STACK_DIRECTION == 0; need run-time code. */
92
93 static int stack_dir; /* 1 or -1 once known. */
94 # define STACK_DIR stack_dir
95
96 static void
97 find_stack_direction (void)
98 {
99 static char *addr = NULL; /* Address of first `dummy', once known. */
100 auto char dummy; /* To get stack address. */
101
102 if (addr == NULL)
103 { /* Initial entry. */
104 addr = ADDRESS_FUNCTION (dummy);
105
106 find_stack_direction (); /* Recurse once. */
107 }
108 else
109 {
110 /* Second entry. */
111 if (ADDRESS_FUNCTION (dummy) > addr)
112 stack_dir = 1; /* Stack grew upward. */
113 else
114 stack_dir = -1; /* Stack grew downward. */
115 }
116 }
117
118 # endif /* STACK_DIRECTION == 0 */
119
120 /* An "alloca header" is used to:
121 (a) chain together all alloca'ed blocks;
122 (b) keep track of stack depth.
123
124 It is very important that sizeof(header) agree with malloc
125 alignment chunk size. The following default should work okay. */
126
127 # ifndef ALIGN_SIZE
128 # define ALIGN_SIZE sizeof(double)
129 # endif
130
131 typedef union hdr
132 {
133 char align[ALIGN_SIZE]; /* To force sizeof(header). */
134 struct
135 {
136 union hdr *next; /* For chaining headers. */
137 char *deep; /* For stack depth measure. */
138 } h;
139 } header;
140
141 static header *last_alloca_header = NULL; /* -> last alloca header. */
142
143 /* Return a pointer to at least SIZE bytes of storage,
144 which will be automatically reclaimed upon exit from
145 the procedure that called alloca. Originally, this space
146 was supposed to be taken from the current stack frame of the
147 caller, but that method cannot be made to work for some
148 implementations of C, for example under Gould's UTX/32. */
149
150 void *
151 alloca (size_t size)
152 {
153 auto char probe; /* Probes stack depth: */
154 register char *depth = ADDRESS_FUNCTION (probe);
155
156 # if STACK_DIRECTION == 0
157 if (STACK_DIR == 0) /* Unknown growth direction. */
158 find_stack_direction ();
159 # endif
160
161 /* Reclaim garbage, defined as all alloca'd storage that
162 was allocated from deeper in the stack than currently. */
163
164 {
165 register header *hp; /* Traverses linked list. */
166
167 # ifdef emacs
168 BLOCK_INPUT;
169 # endif
170
171 for (hp = last_alloca_header; hp != NULL;)
172 if ((STACK_DIR > 0 && hp->h.deep > depth)
173 || (STACK_DIR < 0 && hp->h.deep < depth))
174 {
175 register header *np = hp->h.next;
176
177 free (hp); /* Collect garbage. */
178
179 hp = np; /* -> next header. */
180 }
181 else
182 break; /* Rest are not deeper. */
183
184 last_alloca_header = hp; /* -> last valid storage. */
185
186 # ifdef emacs
187 UNBLOCK_INPUT;
188 # endif
189 }
190
191 if (size == 0)
192 return NULL; /* No allocation required. */
193
194 /* Allocate combined header + user data storage. */
195
196 {
197 /* Address of header. */
198 register header *new;
199
200 size_t combined_size = sizeof (header) + size;
201 if (combined_size < sizeof (header))
202 memory_full ();
203
204 new = malloc (combined_size);
205
206 if (! new)
207 memory_full ();
208
209 new->h.next = last_alloca_header;
210 new->h.deep = depth;
211
212 last_alloca_header = new;
213
214 /* User storage begins just after header. */
215
216 return (void *) (new + 1);
217 }
218 }
219
220 # if defined (CRAY) && defined (CRAY_STACKSEG_END)
221
222 # ifdef DEBUG_I00AFUNC
223 # include <stdio.h>
224 # endif
225
226 # ifndef CRAY_STACK
227 # define CRAY_STACK
228 # ifndef CRAY2
229 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
230 struct stack_control_header
231 {
232 long shgrow:32; /* Number of times stack has grown. */
233 long shaseg:32; /* Size of increments to stack. */
234 long shhwm:32; /* High water mark of stack. */
235 long shsize:32; /* Current size of stack (all segments). */
236 };
237
238 /* The stack segment linkage control information occurs at
239 the high-address end of a stack segment. (The stack
240 grows from low addresses to high addresses.) The initial
241 part of the stack segment linkage control information is
242 0200 (octal) words. This provides for register storage
243 for the routine which overflows the stack. */
244
245 struct stack_segment_linkage
246 {
247 long ss[0200]; /* 0200 overflow words. */
248 long sssize:32; /* Number of words in this segment. */
249 long ssbase:32; /* Offset to stack base. */
250 long:32;
251 long sspseg:32; /* Offset to linkage control of previous
252 segment of stack. */
253 long:32;
254 long sstcpt:32; /* Pointer to task common address block. */
255 long sscsnm; /* Private control structure number for
256 microtasking. */
257 long ssusr1; /* Reserved for user. */
258 long ssusr2; /* Reserved for user. */
259 long sstpid; /* Process ID for pid based multi-tasking. */
260 long ssgvup; /* Pointer to multitasking thread giveup. */
261 long sscray[7]; /* Reserved for Cray Research. */
262 long ssa0;
263 long ssa1;
264 long ssa2;
265 long ssa3;
266 long ssa4;
267 long ssa5;
268 long ssa6;
269 long ssa7;
270 long sss0;
271 long sss1;
272 long sss2;
273 long sss3;
274 long sss4;
275 long sss5;
276 long sss6;
277 long sss7;
278 };
279
280 # else /* CRAY2 */
281 /* The following structure defines the vector of words
282 returned by the STKSTAT library routine. */
283 struct stk_stat
284 {
285 long now; /* Current total stack size. */
286 long maxc; /* Amount of contiguous space which would
287 be required to satisfy the maximum
288 stack demand to date. */
289 long high_water; /* Stack high-water mark. */
290 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
291 long hits; /* Number of internal buffer hits. */
292 long extends; /* Number of block extensions. */
293 long stko_mallocs; /* Block allocations by $STKOFEN. */
294 long underflows; /* Number of stack underflow calls ($STKRETN). */
295 long stko_free; /* Number of deallocations by $STKRETN. */
296 long stkm_free; /* Number of deallocations by $STKMRET. */
297 long segments; /* Current number of stack segments. */
298 long maxs; /* Maximum number of stack segments so far. */
299 long pad_size; /* Stack pad size. */
300 long current_address; /* Current stack segment address. */
301 long current_size; /* Current stack segment size. This
302 number is actually corrupted by STKSTAT to
303 include the fifteen word trailer area. */
304 long initial_address; /* Address of initial segment. */
305 long initial_size; /* Size of initial segment. */
306 };
307
308 /* The following structure describes the data structure which trails
309 any stack segment. I think that the description in 'asdef' is
310 out of date. I only describe the parts that I am sure about. */
311
312 struct stk_trailer
313 {
314 long this_address; /* Address of this block. */
315 long this_size; /* Size of this block (does not include
316 this trailer). */
317 long unknown2;
318 long unknown3;
319 long link; /* Address of trailer block of previous
320 segment. */
321 long unknown5;
322 long unknown6;
323 long unknown7;
324 long unknown8;
325 long unknown9;
326 long unknown10;
327 long unknown11;
328 long unknown12;
329 long unknown13;
330 long unknown14;
331 };
332
333 # endif /* CRAY2 */
334 # endif /* not CRAY_STACK */
335
336 # ifdef CRAY2
337 /* Determine a "stack measure" for an arbitrary ADDRESS.
338 I doubt that "lint" will like this much. */
339
340 static long
341 i00afunc (long *address)
342 {
343 struct stk_stat status;
344 struct stk_trailer *trailer;
345 long *block, size;
346 long result = 0;
347
348 /* We want to iterate through all of the segments. The first
349 step is to get the stack status structure. We could do this
350 more quickly and more directly, perhaps, by referencing the
351 $LM00 common block, but I know that this works. */
352
353 STKSTAT (&status);
354
355 /* Set up the iteration. */
356
357 trailer = (struct stk_trailer *) (status.current_address
358 + status.current_size
359 - 15);
360
361 /* There must be at least one stack segment. Therefore it is
362 a fatal error if "trailer" is null. */
363
364 if (trailer == 0)
365 abort ();
366
367 /* Discard segments that do not contain our argument address. */
368
369 while (trailer != 0)
370 {
371 block = (long *) trailer->this_address;
372 size = trailer->this_size;
373 if (block == 0 || size == 0)
374 abort ();
375 trailer = (struct stk_trailer *) trailer->link;
376 if ((block <= address) && (address < (block + size)))
377 break;
378 }
379
380 /* Set the result to the offset in this segment and add the sizes
381 of all predecessor segments. */
382
383 result = address - block;
384
385 if (trailer == 0)
386 {
387 return result;
388 }
389
390 do
391 {
392 if (trailer->this_size <= 0)
393 abort ();
394 result += trailer->this_size;
395 trailer = (struct stk_trailer *) trailer->link;
396 }
397 while (trailer != 0);
398
399 /* We are done. Note that if you present a bogus address (one
400 not in any segment), you will get a different number back, formed
401 from subtracting the address of the first block. This is probably
402 not what you want. */
403
404 return (result);
405 }
406
407 # else /* not CRAY2 */
408 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
409 Determine the number of the cell within the stack,
410 given the address of the cell. The purpose of this
411 routine is to linearize, in some sense, stack addresses
412 for alloca. */
413
414 static long
415 i00afunc (long address)
416 {
417 long stkl = 0;
418
419 long size, pseg, this_segment, stack;
420 long result = 0;
421
422 struct stack_segment_linkage *ssptr;
423
424 /* Register B67 contains the address of the end of the
425 current stack segment. If you (as a subprogram) store
426 your registers on the stack and find that you are past
427 the contents of B67, you have overflowed the segment.
428
429 B67 also points to the stack segment linkage control
430 area, which is what we are really interested in. */
431
432 stkl = CRAY_STACKSEG_END ();
433 ssptr = (struct stack_segment_linkage *) stkl;
434
435 /* If one subtracts 'size' from the end of the segment,
436 one has the address of the first word of the segment.
437
438 If this is not the first segment, 'pseg' will be
439 nonzero. */
440
441 pseg = ssptr->sspseg;
442 size = ssptr->sssize;
443
444 this_segment = stkl - size;
445
446 /* It is possible that calling this routine itself caused
447 a stack overflow. Discard stack segments which do not
448 contain the target address. */
449
450 while (!(this_segment <= address && address <= stkl))
451 {
452 # ifdef DEBUG_I00AFUNC
453 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
454 # endif
455 if (pseg == 0)
456 break;
457 stkl = stkl - pseg;
458 ssptr = (struct stack_segment_linkage *) stkl;
459 size = ssptr->sssize;
460 pseg = ssptr->sspseg;
461 this_segment = stkl - size;
462 }
463
464 result = address - this_segment;
465
466 /* If you subtract pseg from the current end of the stack,
467 you get the address of the previous stack segment's end.
468 This seems a little convoluted to me, but I'll bet you save
469 a cycle somewhere. */
470
471 while (pseg != 0)
472 {
473 # ifdef DEBUG_I00AFUNC
474 fprintf (stderr, "%011o %011o\n", pseg, size);
475 # endif
476 stkl = stkl - pseg;
477 ssptr = (struct stack_segment_linkage *) stkl;
478 size = ssptr->sssize;
479 pseg = ssptr->sspseg;
480 result += size;
481 }
482 return (result);
483 }
484
485 # endif /* not CRAY2 */
486 # endif /* CRAY */
487
488 # endif /* no alloca */
489 #endif /* not GCC version 3 */