1 /* $NetBSD: alloca.c,v 1.1.1.1 2016/01/10 21:36:18 christos Exp $ */
2
3 /* alloca.c -- allocate automatically reclaimed memory
4 (Mostly) portable public-domain implementation -- D A Gwyn
5
6 This implementation of the PWB library alloca function,
7 which is used to allocate space off the run-time stack so
8 that it is automatically reclaimed upon procedure exit,
9 was inspired by discussions with J. Q. Johnson of Cornell.
10 J.Otto Tennant <jot@cray.com> contributed the Cray support.
11
12 There are some preprocessor constants that can
13 be defined when compiling for your specific system, for
14 improved efficiency; however, the defaults should be okay.
15
16 The general concept of this implementation is to keep
17 track of all alloca-allocated blocks, and reclaim any
18 that are found to be deeper in the stack than the current
19 invocation. This heuristic does not reclaim storage as
20 soon as it becomes invalid, but it will do so eventually.
21
22 As a special case, alloca(0) reclaims storage without
23 allocating any. It is a good idea to use alloca(0) in
24 your main control loop, etc. to force garbage collection. */
25
26 #ifdef HAVE_CONFIG_H
27 # include <config.h>
28 #endif
29
30 #if HAVE_STRING_H
31 # include <string.h>
32 #endif
33 #if HAVE_STDLIB_H
34 # include <stdlib.h>
35 #endif
36
37 #ifdef emacs
38 # include "blockinput.h"
39 #endif
40
41 /* If compiling with GCC 2, this file's not needed. */
42 #if !defined (__GNUC__) || __GNUC__ < 2
43
44 /* If someone has defined alloca as a macro,
45 there must be some other way alloca is supposed to work. */
46 # ifndef alloca
47
48 # ifdef emacs
49 # ifdef static
50 /* actually, only want this if static is defined as ""
51 -- this is for usg, in which emacs must undefine static
52 in order to make unexec workable
53 */
54 # ifndef STACK_DIRECTION
55 you
56 lose
57 -- must know STACK_DIRECTION at compile-time
58 # endif /* STACK_DIRECTION undefined */
59 # endif /* static */
60 # endif /* emacs */
61
62 /* If your stack is a linked list of frames, you have to
63 provide an "address metric" ADDRESS_FUNCTION macro. */
64
65 # if defined (CRAY) && defined (CRAY_STACKSEG_END)
66 long i00afunc ();
67 # define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
68 # else
69 # define ADDRESS_FUNCTION(arg) &(arg)
70 # endif
71
72 # if __STDC__
73 typedef void *pointer;
74 # else
75 typedef char *pointer;
76 # endif
77
78 # ifndef NULL
79 # define NULL 0
80 # endif
81
82 /* Different portions of Emacs need to call different versions of
83 malloc. The Emacs executable needs alloca to call xmalloc, because
84 ordinary malloc isn't protected from input signals. On the other
85 hand, the utilities in lib-src need alloca to call malloc; some of
86 them are very simple, and don't have an xmalloc routine.
87
88 Non-Emacs programs expect this to call xmalloc.
89
90 Callers below should use malloc. */
91
92 # ifndef emacs
93 # define malloc xmalloc
94 # endif
95 extern pointer malloc ();
96
97 /* Define STACK_DIRECTION if you know the direction of stack
98 growth for your system; otherwise it will be automatically
99 deduced at run-time.
100
101 STACK_DIRECTION > 0 => grows toward higher addresses
102 STACK_DIRECTION < 0 => grows toward lower addresses
103 STACK_DIRECTION = 0 => direction of growth unknown */
104
105 # ifndef STACK_DIRECTION
106 # define STACK_DIRECTION 0 /* Direction unknown. */
107 # endif
108
109 # if STACK_DIRECTION != 0
110
111 # define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
112
113 # else /* STACK_DIRECTION == 0; need run-time code. */
114
115 static int stack_dir; /* 1 or -1 once known. */
116 # define STACK_DIR stack_dir
117
118 static void
find_stack_direction()119 find_stack_direction ()
120 {
121 static char *addr = NULL; /* Address of first `dummy', once known. */
122 auto char dummy; /* To get stack address. */
123
124 if (addr == NULL)
125 { /* Initial entry. */
126 addr = ADDRESS_FUNCTION (dummy);
127
128 find_stack_direction (); /* Recurse once. */
129 }
130 else
131 {
132 /* Second entry. */
133 if (ADDRESS_FUNCTION (dummy) > addr)
134 stack_dir = 1; /* Stack grew upward. */
135 else
136 stack_dir = -1; /* Stack grew downward. */
137 }
138 }
139
140 # endif /* STACK_DIRECTION == 0 */
141
142 /* An "alloca header" is used to:
143 (a) chain together all alloca'ed blocks;
144 (b) keep track of stack depth.
145
146 It is very important that sizeof(header) agree with malloc
147 alignment chunk size. The following default should work okay. */
148
149 # ifndef ALIGN_SIZE
150 # define ALIGN_SIZE sizeof(double)
151 # endif
152
153 typedef union hdr
154 {
155 char align[ALIGN_SIZE]; /* To force sizeof(header). */
156 struct
157 {
158 union hdr *next; /* For chaining headers. */
159 char *deep; /* For stack depth measure. */
160 } h;
161 } header;
162
163 static header *last_alloca_header = NULL; /* -> last alloca header. */
164
165 /* Return a pointer to at least SIZE bytes of storage,
166 which will be automatically reclaimed upon exit from
167 the procedure that called alloca. Originally, this space
168 was supposed to be taken from the current stack frame of the
169 caller, but that method cannot be made to work for some
170 implementations of C, for example under Gould's UTX/32. */
171
172 pointer
alloca(unsigned size)173 alloca (unsigned size)
174 {
175 auto char probe; /* Probes stack depth: */
176 register char *depth = ADDRESS_FUNCTION (probe);
177
178 # if STACK_DIRECTION == 0
179 if (STACK_DIR == 0) /* Unknown growth direction. */
180 find_stack_direction ();
181 # endif
182
183 /* Reclaim garbage, defined as all alloca'd storage that
184 was allocated from deeper in the stack than currently. */
185
186 {
187 register header *hp; /* Traverses linked list. */
188
189 # ifdef emacs
190 BLOCK_INPUT;
191 # endif
192
193 for (hp = last_alloca_header; hp != NULL;)
194 if ((STACK_DIR > 0 && hp->h.deep > depth)
195 || (STACK_DIR < 0 && hp->h.deep < depth))
196 {
197 register header *np = hp->h.next;
198
199 free ((pointer) hp); /* Collect garbage. */
200
201 hp = np; /* -> next header. */
202 }
203 else
204 break; /* Rest are not deeper. */
205
206 last_alloca_header = hp; /* -> last valid storage. */
207
208 # ifdef emacs
209 UNBLOCK_INPUT;
210 # endif
211 }
212
213 if (size == 0)
214 return NULL; /* No allocation required. */
215
216 /* Allocate combined header + user data storage. */
217
218 {
219 register pointer new = malloc (sizeof (header) + size);
220 /* Address of header. */
221
222 if (new == 0)
223 abort();
224
225 ((header *) new)->h.next = last_alloca_header;
226 ((header *) new)->h.deep = depth;
227
228 last_alloca_header = (header *) new;
229
230 /* User storage begins just after header. */
231
232 return (pointer) ((char *) new + sizeof (header));
233 }
234 }
235
236 # if defined (CRAY) && defined (CRAY_STACKSEG_END)
237
238 # ifdef DEBUG_I00AFUNC
239 # include <stdio.h>
240 # endif
241
242 # ifndef CRAY_STACK
243 # define CRAY_STACK
244 # ifndef CRAY2
245 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
246 struct stack_control_header
247 {
248 long shgrow:32; /* Number of times stack has grown. */
249 long shaseg:32; /* Size of increments to stack. */
250 long shhwm:32; /* High water mark of stack. */
251 long shsize:32; /* Current size of stack (all segments). */
252 };
253
254 /* The stack segment linkage control information occurs at
255 the high-address end of a stack segment. (The stack
256 grows from low addresses to high addresses.) The initial
257 part of the stack segment linkage control information is
258 0200 (octal) words. This provides for register storage
259 for the routine which overflows the stack. */
260
261 struct stack_segment_linkage
262 {
263 long ss[0200]; /* 0200 overflow words. */
264 long sssize:32; /* Number of words in this segment. */
265 long ssbase:32; /* Offset to stack base. */
266 long:32;
267 long sspseg:32; /* Offset to linkage control of previous
268 segment of stack. */
269 long:32;
270 long sstcpt:32; /* Pointer to task common address block. */
271 long sscsnm; /* Private control structure number for
272 microtasking. */
273 long ssusr1; /* Reserved for user. */
274 long ssusr2; /* Reserved for user. */
275 long sstpid; /* Process ID for pid based multi-tasking. */
276 long ssgvup; /* Pointer to multitasking thread giveup. */
277 long sscray[7]; /* Reserved for Cray Research. */
278 long ssa0;
279 long ssa1;
280 long ssa2;
281 long ssa3;
282 long ssa4;
283 long ssa5;
284 long ssa6;
285 long ssa7;
286 long sss0;
287 long sss1;
288 long sss2;
289 long sss3;
290 long sss4;
291 long sss5;
292 long sss6;
293 long sss7;
294 };
295
296 # else /* CRAY2 */
297 /* The following structure defines the vector of words
298 returned by the STKSTAT library routine. */
299 struct stk_stat
300 {
301 long now; /* Current total stack size. */
302 long maxc; /* Amount of contiguous space which would
303 be required to satisfy the maximum
304 stack demand to date. */
305 long high_water; /* Stack high-water mark. */
306 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
307 long hits; /* Number of internal buffer hits. */
308 long extends; /* Number of block extensions. */
309 long stko_mallocs; /* Block allocations by $STKOFEN. */
310 long underflows; /* Number of stack underflow calls ($STKRETN). */
311 long stko_free; /* Number of deallocations by $STKRETN. */
312 long stkm_free; /* Number of deallocations by $STKMRET. */
313 long segments; /* Current number of stack segments. */
314 long maxs; /* Maximum number of stack segments so far. */
315 long pad_size; /* Stack pad size. */
316 long current_address; /* Current stack segment address. */
317 long current_size; /* Current stack segment size. This
318 number is actually corrupted by STKSTAT to
319 include the fifteen word trailer area. */
320 long initial_address; /* Address of initial segment. */
321 long initial_size; /* Size of initial segment. */
322 };
323
324 /* The following structure describes the data structure which trails
325 any stack segment. I think that the description in 'asdef' is
326 out of date. I only describe the parts that I am sure about. */
327
328 struct stk_trailer
329 {
330 long this_address; /* Address of this block. */
331 long this_size; /* Size of this block (does not include
332 this trailer). */
333 long unknown2;
334 long unknown3;
335 long link; /* Address of trailer block of previous
336 segment. */
337 long unknown5;
338 long unknown6;
339 long unknown7;
340 long unknown8;
341 long unknown9;
342 long unknown10;
343 long unknown11;
344 long unknown12;
345 long unknown13;
346 long unknown14;
347 };
348
349 # endif /* CRAY2 */
350 # endif /* not CRAY_STACK */
351
352 # ifdef CRAY2
353 /* Determine a "stack measure" for an arbitrary ADDRESS.
354 I doubt that "lint" will like this much. */
355
356 static long
i00afunc(long * address)357 i00afunc (long *address)
358 {
359 struct stk_stat status;
360 struct stk_trailer *trailer;
361 long *block, size;
362 long result = 0;
363
364 /* We want to iterate through all of the segments. The first
365 step is to get the stack status structure. We could do this
366 more quickly and more directly, perhaps, by referencing the
367 $LM00 common block, but I know that this works. */
368
369 STKSTAT (&status);
370
371 /* Set up the iteration. */
372
373 trailer = (struct stk_trailer *) (status.current_address
374 + status.current_size
375 - 15);
376
377 /* There must be at least one stack segment. Therefore it is
378 a fatal error if "trailer" is null. */
379
380 if (trailer == 0)
381 abort ();
382
383 /* Discard segments that do not contain our argument address. */
384
385 while (trailer != 0)
386 {
387 block = (long *) trailer->this_address;
388 size = trailer->this_size;
389 if (block == 0 || size == 0)
390 abort ();
391 trailer = (struct stk_trailer *) trailer->link;
392 if ((block <= address) && (address < (block + size)))
393 break;
394 }
395
396 /* Set the result to the offset in this segment and add the sizes
397 of all predecessor segments. */
398
399 result = address - block;
400
401 if (trailer == 0)
402 {
403 return result;
404 }
405
406 do
407 {
408 if (trailer->this_size <= 0)
409 abort ();
410 result += trailer->this_size;
411 trailer = (struct stk_trailer *) trailer->link;
412 }
413 while (trailer != 0);
414
415 /* We are done. Note that if you present a bogus address (one
416 not in any segment), you will get a different number back, formed
417 from subtracting the address of the first block. This is probably
418 not what you want. */
419
420 return (result);
421 }
422
423 # else /* not CRAY2 */
424 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
425 Determine the number of the cell within the stack,
426 given the address of the cell. The purpose of this
427 routine is to linearize, in some sense, stack addresses
428 for alloca. */
429
430 static long
i00afunc(long address)431 i00afunc (long address)
432 {
433 long stkl = 0;
434
435 long size, pseg, this_segment, stack;
436 long result = 0;
437
438 struct stack_segment_linkage *ssptr;
439
440 /* Register B67 contains the address of the end of the
441 current stack segment. If you (as a subprogram) store
442 your registers on the stack and find that you are past
443 the contents of B67, you have overflowed the segment.
444
445 B67 also points to the stack segment linkage control
446 area, which is what we are really interested in. */
447
448 stkl = CRAY_STACKSEG_END ();
449 ssptr = (struct stack_segment_linkage *) stkl;
450
451 /* If one subtracts 'size' from the end of the segment,
452 one has the address of the first word of the segment.
453
454 If this is not the first segment, 'pseg' will be
455 nonzero. */
456
457 pseg = ssptr->sspseg;
458 size = ssptr->sssize;
459
460 this_segment = stkl - size;
461
462 /* It is possible that calling this routine itself caused
463 a stack overflow. Discard stack segments which do not
464 contain the target address. */
465
466 while (!(this_segment <= address && address <= stkl))
467 {
468 # ifdef DEBUG_I00AFUNC
469 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
470 # endif
471 if (pseg == 0)
472 break;
473 stkl = stkl - pseg;
474 ssptr = (struct stack_segment_linkage *) stkl;
475 size = ssptr->sssize;
476 pseg = ssptr->sspseg;
477 this_segment = stkl - size;
478 }
479
480 result = address - this_segment;
481
482 /* If you subtract pseg from the current end of the stack,
483 you get the address of the previous stack segment's end.
484 This seems a little convoluted to me, but I'll bet you save
485 a cycle somewhere. */
486
487 while (pseg != 0)
488 {
489 # ifdef DEBUG_I00AFUNC
490 fprintf (stderr, "%011o %011o\n", pseg, size);
491 # endif
492 stkl = stkl - pseg;
493 ssptr = (struct stack_segment_linkage *) stkl;
494 size = ssptr->sssize;
495 pseg = ssptr->sspseg;
496 result += size;
497 }
498 return (result);
499 }
500
501 # endif /* not CRAY2 */
502 # endif /* CRAY */
503
504 # endif /* no alloca */
505 #endif /* not GCC version 2 */
506