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8690e634 JK |
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 int | |
97 | find_stack_direction (int *addr, int depth) | |
98 | { | |
99 | int dir, dummy = 0; | |
100 | if (! addr) | |
101 | addr = &dummy; | |
102 | *addr = addr < &dummy ? 1 : addr == &dummy ? 0 : -1; | |
103 | dir = depth ? find_stack_direction (addr, depth - 1) : 0; | |
104 | return dir + dummy; | |
105 | } | |
106 | ||
107 | # endif /* STACK_DIRECTION == 0 */ | |
108 | ||
109 | /* An "alloca header" is used to: | |
110 | (a) chain together all alloca'ed blocks; | |
111 | (b) keep track of stack depth. | |
112 | ||
113 | It is very important that sizeof(header) agree with malloc | |
114 | alignment chunk size. The following default should work okay. */ | |
115 | ||
116 | # ifndef ALIGN_SIZE | |
117 | # define ALIGN_SIZE sizeof(double) | |
118 | # endif | |
119 | ||
120 | typedef union hdr | |
121 | { | |
122 | char align[ALIGN_SIZE]; /* To force sizeof(header). */ | |
123 | struct | |
124 | { | |
125 | union hdr *next; /* For chaining headers. */ | |
126 | char *deep; /* For stack depth measure. */ | |
127 | } h; | |
128 | } header; | |
129 | ||
130 | static header *last_alloca_header = NULL; /* -> last alloca header. */ | |
131 | ||
132 | /* Return a pointer to at least SIZE bytes of storage, | |
133 | which will be automatically reclaimed upon exit from | |
134 | the procedure that called alloca. Originally, this space | |
135 | was supposed to be taken from the current stack frame of the | |
136 | caller, but that method cannot be made to work for some | |
137 | implementations of C, for example under Gould's UTX/32. */ | |
138 | ||
139 | void * | |
140 | alloca (size_t size) | |
141 | { | |
142 | auto char probe; /* Probes stack depth: */ | |
143 | register char *depth = ADDRESS_FUNCTION (probe); | |
144 | ||
145 | # if STACK_DIRECTION == 0 | |
146 | if (STACK_DIR == 0) /* Unknown growth direction. */ | |
147 | STACK_DIR = find_stack_direction (NULL, (size & 1) + 20); | |
148 | # endif | |
149 | ||
150 | /* Reclaim garbage, defined as all alloca'd storage that | |
151 | was allocated from deeper in the stack than currently. */ | |
152 | ||
153 | { | |
154 | register header *hp; /* Traverses linked list. */ | |
155 | ||
156 | # ifdef emacs | |
157 | BLOCK_INPUT; | |
158 | # endif | |
159 | ||
160 | for (hp = last_alloca_header; hp != NULL;) | |
161 | if ((STACK_DIR > 0 && hp->h.deep > depth) | |
162 | || (STACK_DIR < 0 && hp->h.deep < depth)) | |
163 | { | |
164 | register header *np = hp->h.next; | |
165 | ||
166 | free (hp); /* Collect garbage. */ | |
167 | ||
168 | hp = np; /* -> next header. */ | |
169 | } | |
170 | else | |
171 | break; /* Rest are not deeper. */ | |
172 | ||
173 | last_alloca_header = hp; /* -> last valid storage. */ | |
174 | ||
175 | # ifdef emacs | |
176 | UNBLOCK_INPUT; | |
177 | # endif | |
178 | } | |
179 | ||
180 | if (size == 0) | |
181 | return NULL; /* No allocation required. */ | |
182 | ||
183 | /* Allocate combined header + user data storage. */ | |
184 | ||
185 | { | |
186 | /* Address of header. */ | |
187 | register header *new; | |
188 | ||
189 | size_t combined_size = sizeof (header) + size; | |
190 | if (combined_size < sizeof (header)) | |
191 | memory_full (); | |
192 | ||
193 | new = malloc (combined_size); | |
194 | ||
195 | if (! new) | |
196 | memory_full (); | |
197 | ||
198 | new->h.next = last_alloca_header; | |
199 | new->h.deep = depth; | |
200 | ||
201 | last_alloca_header = new; | |
202 | ||
203 | /* User storage begins just after header. */ | |
204 | ||
205 | return (void *) (new + 1); | |
206 | } | |
207 | } | |
208 | ||
209 | # if defined (CRAY) && defined (CRAY_STACKSEG_END) | |
210 | ||
211 | # ifdef DEBUG_I00AFUNC | |
212 | # include <stdio.h> | |
213 | # endif | |
214 | ||
215 | # ifndef CRAY_STACK | |
216 | # define CRAY_STACK | |
217 | # ifndef CRAY2 | |
218 | /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */ | |
219 | struct stack_control_header | |
220 | { | |
221 | long shgrow:32; /* Number of times stack has grown. */ | |
222 | long shaseg:32; /* Size of increments to stack. */ | |
223 | long shhwm:32; /* High water mark of stack. */ | |
224 | long shsize:32; /* Current size of stack (all segments). */ | |
225 | }; | |
226 | ||
227 | /* The stack segment linkage control information occurs at | |
228 | the high-address end of a stack segment. (The stack | |
229 | grows from low addresses to high addresses.) The initial | |
230 | part of the stack segment linkage control information is | |
231 | 0200 (octal) words. This provides for register storage | |
232 | for the routine which overflows the stack. */ | |
233 | ||
234 | struct stack_segment_linkage | |
235 | { | |
236 | long ss[0200]; /* 0200 overflow words. */ | |
237 | long sssize:32; /* Number of words in this segment. */ | |
238 | long ssbase:32; /* Offset to stack base. */ | |
239 | long:32; | |
240 | long sspseg:32; /* Offset to linkage control of previous | |
241 | segment of stack. */ | |
242 | long:32; | |
243 | long sstcpt:32; /* Pointer to task common address block. */ | |
244 | long sscsnm; /* Private control structure number for | |
245 | microtasking. */ | |
246 | long ssusr1; /* Reserved for user. */ | |
247 | long ssusr2; /* Reserved for user. */ | |
248 | long sstpid; /* Process ID for pid based multi-tasking. */ | |
249 | long ssgvup; /* Pointer to multitasking thread giveup. */ | |
250 | long sscray[7]; /* Reserved for Cray Research. */ | |
251 | long ssa0; | |
252 | long ssa1; | |
253 | long ssa2; | |
254 | long ssa3; | |
255 | long ssa4; | |
256 | long ssa5; | |
257 | long ssa6; | |
258 | long ssa7; | |
259 | long sss0; | |
260 | long sss1; | |
261 | long sss2; | |
262 | long sss3; | |
263 | long sss4; | |
264 | long sss5; | |
265 | long sss6; | |
266 | long sss7; | |
267 | }; | |
268 | ||
269 | # else /* CRAY2 */ | |
270 | /* The following structure defines the vector of words | |
271 | returned by the STKSTAT library routine. */ | |
272 | struct stk_stat | |
273 | { | |
274 | long now; /* Current total stack size. */ | |
275 | long maxc; /* Amount of contiguous space which would | |
276 | be required to satisfy the maximum | |
277 | stack demand to date. */ | |
278 | long high_water; /* Stack high-water mark. */ | |
279 | long overflows; /* Number of stack overflow ($STKOFEN) calls. */ | |
280 | long hits; /* Number of internal buffer hits. */ | |
281 | long extends; /* Number of block extensions. */ | |
282 | long stko_mallocs; /* Block allocations by $STKOFEN. */ | |
283 | long underflows; /* Number of stack underflow calls ($STKRETN). */ | |
284 | long stko_free; /* Number of deallocations by $STKRETN. */ | |
285 | long stkm_free; /* Number of deallocations by $STKMRET. */ | |
286 | long segments; /* Current number of stack segments. */ | |
287 | long maxs; /* Maximum number of stack segments so far. */ | |
288 | long pad_size; /* Stack pad size. */ | |
289 | long current_address; /* Current stack segment address. */ | |
290 | long current_size; /* Current stack segment size. This | |
291 | number is actually corrupted by STKSTAT to | |
292 | include the fifteen word trailer area. */ | |
293 | long initial_address; /* Address of initial segment. */ | |
294 | long initial_size; /* Size of initial segment. */ | |
295 | }; | |
296 | ||
297 | /* The following structure describes the data structure which trails | |
298 | any stack segment. I think that the description in 'asdef' is | |
299 | out of date. I only describe the parts that I am sure about. */ | |
300 | ||
301 | struct stk_trailer | |
302 | { | |
303 | long this_address; /* Address of this block. */ | |
304 | long this_size; /* Size of this block (does not include | |
305 | this trailer). */ | |
306 | long unknown2; | |
307 | long unknown3; | |
308 | long link; /* Address of trailer block of previous | |
309 | segment. */ | |
310 | long unknown5; | |
311 | long unknown6; | |
312 | long unknown7; | |
313 | long unknown8; | |
314 | long unknown9; | |
315 | long unknown10; | |
316 | long unknown11; | |
317 | long unknown12; | |
318 | long unknown13; | |
319 | long unknown14; | |
320 | }; | |
321 | ||
322 | # endif /* CRAY2 */ | |
323 | # endif /* not CRAY_STACK */ | |
324 | ||
325 | # ifdef CRAY2 | |
326 | /* Determine a "stack measure" for an arbitrary ADDRESS. | |
327 | I doubt that "lint" will like this much. */ | |
328 | ||
329 | static long | |
330 | i00afunc (long *address) | |
331 | { | |
332 | struct stk_stat status; | |
333 | struct stk_trailer *trailer; | |
334 | long *block, size; | |
335 | long result = 0; | |
336 | ||
337 | /* We want to iterate through all of the segments. The first | |
338 | step is to get the stack status structure. We could do this | |
339 | more quickly and more directly, perhaps, by referencing the | |
340 | $LM00 common block, but I know that this works. */ | |
341 | ||
342 | STKSTAT (&status); | |
343 | ||
344 | /* Set up the iteration. */ | |
345 | ||
346 | trailer = (struct stk_trailer *) (status.current_address | |
347 | + status.current_size | |
348 | - 15); | |
349 | ||
350 | /* There must be at least one stack segment. Therefore it is | |
351 | a fatal error if "trailer" is null. */ | |
352 | ||
353 | if (trailer == 0) | |
354 | abort (); | |
355 | ||
356 | /* Discard segments that do not contain our argument address. */ | |
357 | ||
358 | while (trailer != 0) | |
359 | { | |
360 | block = (long *) trailer->this_address; | |
361 | size = trailer->this_size; | |
362 | if (block == 0 || size == 0) | |
363 | abort (); | |
364 | trailer = (struct stk_trailer *) trailer->link; | |
365 | if ((block <= address) && (address < (block + size))) | |
366 | break; | |
367 | } | |
368 | ||
369 | /* Set the result to the offset in this segment and add the sizes | |
370 | of all predecessor segments. */ | |
371 | ||
372 | result = address - block; | |
373 | ||
374 | if (trailer == 0) | |
375 | { | |
376 | return result; | |
377 | } | |
378 | ||
379 | do | |
380 | { | |
381 | if (trailer->this_size <= 0) | |
382 | abort (); | |
383 | result += trailer->this_size; | |
384 | trailer = (struct stk_trailer *) trailer->link; | |
385 | } | |
386 | while (trailer != 0); | |
387 | ||
388 | /* We are done. Note that if you present a bogus address (one | |
389 | not in any segment), you will get a different number back, formed | |
390 | from subtracting the address of the first block. This is probably | |
391 | not what you want. */ | |
392 | ||
393 | return (result); | |
394 | } | |
395 | ||
396 | # else /* not CRAY2 */ | |
397 | /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP. | |
398 | Determine the number of the cell within the stack, | |
399 | given the address of the cell. The purpose of this | |
400 | routine is to linearize, in some sense, stack addresses | |
401 | for alloca. */ | |
402 | ||
403 | static long | |
404 | i00afunc (long address) | |
405 | { | |
406 | long stkl = 0; | |
407 | ||
408 | long size, pseg, this_segment, stack; | |
409 | long result = 0; | |
410 | ||
411 | struct stack_segment_linkage *ssptr; | |
412 | ||
413 | /* Register B67 contains the address of the end of the | |
414 | current stack segment. If you (as a subprogram) store | |
415 | your registers on the stack and find that you are past | |
416 | the contents of B67, you have overflowed the segment. | |
417 | ||
418 | B67 also points to the stack segment linkage control | |
419 | area, which is what we are really interested in. */ | |
420 | ||
421 | stkl = CRAY_STACKSEG_END (); | |
422 | ssptr = (struct stack_segment_linkage *) stkl; | |
423 | ||
424 | /* If one subtracts 'size' from the end of the segment, | |
425 | one has the address of the first word of the segment. | |
426 | ||
427 | If this is not the first segment, 'pseg' will be | |
428 | nonzero. */ | |
429 | ||
430 | pseg = ssptr->sspseg; | |
431 | size = ssptr->sssize; | |
432 | ||
433 | this_segment = stkl - size; | |
434 | ||
435 | /* It is possible that calling this routine itself caused | |
436 | a stack overflow. Discard stack segments which do not | |
437 | contain the target address. */ | |
438 | ||
439 | while (!(this_segment <= address && address <= stkl)) | |
440 | { | |
441 | # ifdef DEBUG_I00AFUNC | |
442 | fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl); | |
443 | # endif | |
444 | if (pseg == 0) | |
445 | break; | |
446 | stkl = stkl - pseg; | |
447 | ssptr = (struct stack_segment_linkage *) stkl; | |
448 | size = ssptr->sssize; | |
449 | pseg = ssptr->sspseg; | |
450 | this_segment = stkl - size; | |
451 | } | |
452 | ||
453 | result = address - this_segment; | |
454 | ||
455 | /* If you subtract pseg from the current end of the stack, | |
456 | you get the address of the previous stack segment's end. | |
457 | This seems a little convoluted to me, but I'll bet you save | |
458 | a cycle somewhere. */ | |
459 | ||
460 | while (pseg != 0) | |
461 | { | |
462 | # ifdef DEBUG_I00AFUNC | |
463 | fprintf (stderr, "%011o %011o\n", pseg, size); | |
464 | # endif | |
465 | stkl = stkl - pseg; | |
466 | ssptr = (struct stack_segment_linkage *) stkl; | |
467 | size = ssptr->sssize; | |
468 | pseg = ssptr->sspseg; | |
469 | result += size; | |
470 | } | |
471 | return (result); | |
472 | } | |
473 | ||
474 | # endif /* not CRAY2 */ | |
475 | # endif /* CRAY */ | |
476 | ||
477 | # endif /* no alloca */ | |
478 | #endif /* not GCC 2 */ |