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