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