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 use 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
find_stack_direction(void)117 find_stack_direction (void)
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
alloca(unsigned size)171 alloca (unsigned size)
172 {
173 auto char probe; /* Probes stack depth: */
174 register char *depth = ADDRESS_FUNCTION (probe);
175
176 #if STACK_DIRECTION == 0
177 if (STACK_DIR == 0) /* Unknown growth direction. */
178 find_stack_direction ();
179 #endif
180
181 /* Reclaim garbage, defined as all alloca'd storage that
182 was allocated from deeper in the stack than currently. */
183
184 {
185 register header *hp; /* Traverses linked list. */
186
187 #ifdef emacs
188 BLOCK_INPUT;
189 #endif
190
191 for (hp = last_alloca_header; hp != NULL;)
192 if ((STACK_DIR > 0 && hp->h.deep > depth)
193 || (STACK_DIR < 0 && hp->h.deep < depth))
194 {
195 register header *np = hp->h.next;
196
197 free ((pointer) hp); /* Collect garbage. */
198
199 hp = np; /* -> next header. */
200 }
201 else
202 break; /* Rest are not deeper. */
203
204 last_alloca_header = hp; /* -> last valid storage. */
205
206 #ifdef emacs
207 UNBLOCK_INPUT;
208 #endif
209 }
210
211 if (size == 0)
212 return NULL; /* No allocation required. */
213
214 /* Allocate combined header + user data storage. */
215
216 {
217 register pointer new = malloc (sizeof (header) + size);
218 /* Address of header. */
219
220 if (new == 0)
221 abort();
222
223 ((header *) new)->h.next = last_alloca_header;
224 ((header *) new)->h.deep = depth;
225
226 last_alloca_header = (header *) new;
227
228 /* User storage begins just after header. */
229
230 return (pointer) ((char *) new + sizeof (header));
231 }
232 }
233
234 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
235
236 #ifdef DEBUG_I00AFUNC
237 #include <stdio.h>
238 #endif
239
240 #ifndef CRAY_STACK
241 #define CRAY_STACK
242 #ifndef CRAY2
243 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
244 struct stack_control_header
245 {
246 long shgrow:32; /* Number of times stack has grown. */
247 long shaseg:32; /* Size of increments to stack. */
248 long shhwm:32; /* High water mark of stack. */
249 long shsize:32; /* Current size of stack (all segments). */
250 };
251
252 /* The stack segment linkage control information occurs at
253 the high-address end of a stack segment. (The stack
254 grows from low addresses to high addresses.) The initial
255 part of the stack segment linkage control information is
256 0200 (octal) words. This provides for register storage
257 for the routine which overflows the stack. */
258
259 struct stack_segment_linkage
260 {
261 long ss[0200]; /* 0200 overflow words. */
262 long sssize:32; /* Number of words in this segment. */
263 long ssbase:32; /* Offset to stack base. */
264 long:32;
265 long sspseg:32; /* Offset to linkage control of previous
266 segment of stack. */
267 long:32;
268 long sstcpt:32; /* Pointer to task common address block. */
269 long sscsnm; /* Private control structure number for
270 microtasking. */
271 long ssusr1; /* Reserved for user. */
272 long ssusr2; /* Reserved for user. */
273 long sstpid; /* Process ID for pid based multi-tasking. */
274 long ssgvup; /* Pointer to multitasking thread giveup. */
275 long sscray[7]; /* Reserved for Cray Research. */
276 long ssa0;
277 long ssa1;
278 long ssa2;
279 long ssa3;
280 long ssa4;
281 long ssa5;
282 long ssa6;
283 long ssa7;
284 long sss0;
285 long sss1;
286 long sss2;
287 long sss3;
288 long sss4;
289 long sss5;
290 long sss6;
291 long sss7;
292 };
293
294 #else /* CRAY2 */
295 /* The following structure defines the vector of words
296 returned by the STKSTAT library routine. */
297 struct stk_stat
298 {
299 long now; /* Current total stack size. */
300 long maxc; /* Amount of contiguous space which would
301 be required to satisfy the maximum
302 stack demand to date. */
303 long high_water; /* Stack high-water mark. */
304 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
305 long hits; /* Number of internal buffer hits. */
306 long extends; /* Number of block extensions. */
307 long stko_mallocs; /* Block allocations by $STKOFEN. */
308 long underflows; /* Number of stack underflow calls ($STKRETN). */
309 long stko_free; /* Number of deallocations by $STKRETN. */
310 long stkm_free; /* Number of deallocations by $STKMRET. */
311 long segments; /* Current number of stack segments. */
312 long maxs; /* Maximum number of stack segments so far. */
313 long pad_size; /* Stack pad size. */
314 long current_address; /* Current stack segment address. */
315 long current_size; /* Current stack segment size. This
316 number is actually corrupted by STKSTAT to
317 include the fifteen word trailer area. */
318 long initial_address; /* Address of initial segment. */
319 long initial_size; /* Size of initial segment. */
320 };
321
322 /* The following structure describes the data structure which trails
323 any stack segment. I think that the description in 'asdef' is
324 out of date. I only describe the parts that I am sure about. */
325
326 struct stk_trailer
327 {
328 long this_address; /* Address of this block. */
329 long this_size; /* Size of this block (does not include
330 this trailer). */
331 long unknown2;
332 long unknown3;
333 long link; /* Address of trailer block of previous
334 segment. */
335 long unknown5;
336 long unknown6;
337 long unknown7;
338 long unknown8;
339 long unknown9;
340 long unknown10;
341 long unknown11;
342 long unknown12;
343 long unknown13;
344 long unknown14;
345 };
346
347 #endif /* CRAY2 */
348 #endif /* not CRAY_STACK */
349
350 #ifdef CRAY2
351 /* Determine a "stack measure" for an arbitrary ADDRESS.
352 I doubt that "lint" will like this much. */
353
354 static long
i00afunc(long * address)355 i00afunc (long *address)
356 {
357 struct stk_stat status;
358 struct stk_trailer *trailer;
359 long *block, size;
360 long result = 0;
361
362 /* We want to iterate through all of the segments. The first
363 step is to get the stack status structure. We could do this
364 more quickly and more directly, perhaps, by referencing the
365 $LM00 common block, but I know that this works. */
366
367 STKSTAT (&status);
368
369 /* Set up the iteration. */
370
371 trailer = (struct stk_trailer *) (status.current_address
372 + status.current_size
373 - 15);
374
375 /* There must be at least one stack segment. Therefore it is
376 a fatal error if "trailer" is null. */
377
378 if (trailer == 0)
379 abort ();
380
381 /* Discard segments that do not contain our argument address. */
382
383 while (trailer != 0)
384 {
385 block = (long *) trailer->this_address;
386 size = trailer->this_size;
387 if (block == 0 || size == 0)
388 abort ();
389 trailer = (struct stk_trailer *) trailer->link;
390 if ((block <= address) && (address < (block + size)))
391 break;
392 }
393
394 /* Set the result to the offset in this segment and add the sizes
395 of all predecessor segments. */
396
397 result = address - block;
398
399 if (trailer == 0)
400 {
401 return result;
402 }
403
404 do
405 {
406 if (trailer->this_size <= 0)
407 abort ();
408 result += trailer->this_size;
409 trailer = (struct stk_trailer *) trailer->link;
410 }
411 while (trailer != 0);
412
413 /* We are done. Note that if you present a bogus address (one
414 not in any segment), you will get a different number back, formed
415 from subtracting the address of the first block. This is probably
416 not what you want. */
417
418 return (result);
419 }
420
421 #else /* not CRAY2 */
422 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
423 Determine the number of the cell within the stack,
424 given the address of the cell. The purpose of this
425 routine is to linearize, in some sense, stack addresses
426 for alloca. */
427
428 static long
i00afunc(long address)429 i00afunc (long address)
430 {
431 long stkl = 0;
432
433 long size, pseg, this_segment, stack;
434 long result = 0;
435
436 struct stack_segment_linkage *ssptr;
437
438 /* Register B67 contains the address of the end of the
439 current stack segment. If you (as a subprogram) store
440 your registers on the stack and find that you are past
441 the contents of B67, you have overflowed the segment.
442
443 B67 also points to the stack segment linkage control
444 area, which is what we are really interested in. */
445
446 stkl = CRAY_STACKSEG_END ();
447 ssptr = (struct stack_segment_linkage *) stkl;
448
449 /* If one subtracts 'size' from the end of the segment,
450 one has the address of the first word of the segment.
451
452 If this is not the first segment, 'pseg' will be
453 nonzero. */
454
455 pseg = ssptr->sspseg;
456 size = ssptr->sssize;
457
458 this_segment = stkl - size;
459
460 /* It is possible that calling this routine itself caused
461 a stack overflow. Discard stack segments which do not
462 contain the target address. */
463
464 while (!(this_segment <= address && address <= stkl))
465 {
466 #ifdef DEBUG_I00AFUNC
467 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
468 #endif
469 if (pseg == 0)
470 break;
471 stkl = stkl - pseg;
472 ssptr = (struct stack_segment_linkage *) stkl;
473 size = ssptr->sssize;
474 pseg = ssptr->sspseg;
475 this_segment = stkl - size;
476 }
477
478 result = address - this_segment;
479
480 /* If you subtract pseg from the current end of the stack,
481 you get the address of the previous stack segment's end.
482 This seems a little convoluted to me, but I'll bet you save
483 a cycle somewhere. */
484
485 while (pseg != 0)
486 {
487 #ifdef DEBUG_I00AFUNC
488 fprintf (stderr, "%011o %011o\n", pseg, size);
489 #endif
490 stkl = stkl - pseg;
491 ssptr = (struct stack_segment_linkage *) stkl;
492 size = ssptr->sssize;
493 pseg = ssptr->sspseg;
494 result += size;
495 }
496 return (result);
497 }
498
499 #endif /* not CRAY2 */
500 #endif /* CRAY */
501
502 #endif /* no alloca */
503 #endif /* not GCC version 2 */
504