1 /* $NetBSD: alloca.c,v 1.1.1.1 2016/01/14 00:11:29 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 #include <alloca.h>
31
32 #include <string.h>
33 #include <stdlib.h>
34
35 #ifdef emacs
36 # include "lisp.h"
37 # include "blockinput.h"
38 # ifdef EMACS_FREE
39 # undef free
40 # define free EMACS_FREE
41 # endif
42 #else
43 # define memory_full() abort ()
44 #endif
45
46 /* If compiling with GCC 2, this file's not needed. */
47 #if !defined (__GNUC__) || __GNUC__ < 2
48
49 /* If someone has defined alloca as a macro,
50 there must be some other way alloca is supposed to work. */
51 # ifndef alloca
52
53 # ifdef emacs
54 # ifdef static
55 /* actually, only want this if static is defined as ""
56 -- this is for usg, in which emacs must undefine static
57 in order to make unexec workable
58 */
59 # ifndef STACK_DIRECTION
60 you
61 lose
62 -- must know STACK_DIRECTION at compile-time
63 /* Using #error here is not wise since this file should work for
64 old and obscure compilers. */
65 # endif /* STACK_DIRECTION undefined */
66 # endif /* static */
67 # endif /* emacs */
68
69 /* If your stack is a linked list of frames, you have to
70 provide an "address metric" ADDRESS_FUNCTION macro. */
71
72 # if defined (CRAY) && defined (CRAY_STACKSEG_END)
73 long i00afunc ();
74 # define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
75 # else
76 # define ADDRESS_FUNCTION(arg) &(arg)
77 # endif
78
79 /* Define STACK_DIRECTION if you know the direction of stack
80 growth for your system; otherwise it will be automatically
81 deduced at run-time.
82
83 STACK_DIRECTION > 0 => grows toward higher addresses
84 STACK_DIRECTION < 0 => grows toward lower addresses
85 STACK_DIRECTION = 0 => direction of growth unknown */
86
87 # ifndef STACK_DIRECTION
88 # define STACK_DIRECTION 0 /* Direction unknown. */
89 # endif
90
91 # if STACK_DIRECTION != 0
92
93 # define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
94
95 # else /* STACK_DIRECTION == 0; need run-time code. */
96
97 static int stack_dir; /* 1 or -1 once known. */
98 # define STACK_DIR stack_dir
99
100 static void
find_stack_direction(void)101 find_stack_direction (void)
102 {
103 static char *addr = NULL; /* Address of first `dummy', once known. */
104 auto char dummy; /* To get stack address. */
105
106 if (addr == NULL)
107 { /* Initial entry. */
108 addr = ADDRESS_FUNCTION (dummy);
109
110 find_stack_direction (); /* Recurse once. */
111 }
112 else
113 {
114 /* Second entry. */
115 if (ADDRESS_FUNCTION (dummy) > addr)
116 stack_dir = 1; /* Stack grew upward. */
117 else
118 stack_dir = -1; /* Stack grew downward. */
119 }
120 }
121
122 # endif /* STACK_DIRECTION == 0 */
123
124 /* An "alloca header" is used to:
125 (a) chain together all alloca'ed blocks;
126 (b) keep track of stack depth.
127
128 It is very important that sizeof(header) agree with malloc
129 alignment chunk size. The following default should work okay. */
130
131 # ifndef ALIGN_SIZE
132 # define ALIGN_SIZE sizeof(double)
133 # endif
134
135 typedef union hdr
136 {
137 char align[ALIGN_SIZE]; /* To force sizeof(header). */
138 struct
139 {
140 union hdr *next; /* For chaining headers. */
141 char *deep; /* For stack depth measure. */
142 } h;
143 } header;
144
145 static header *last_alloca_header = NULL; /* -> last alloca header. */
146
147 /* Return a pointer to at least SIZE bytes of storage,
148 which will be automatically reclaimed upon exit from
149 the procedure that called alloca. Originally, this space
150 was supposed to be taken from the current stack frame of the
151 caller, but that method cannot be made to work for some
152 implementations of C, for example under Gould's UTX/32. */
153
154 void *
alloca(size_t size)155 alloca (size_t 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 # ifdef emacs
172 BLOCK_INPUT;
173 # endif
174
175 for (hp = last_alloca_header; hp != NULL;)
176 if ((STACK_DIR > 0 && hp->h.deep > depth)
177 || (STACK_DIR < 0 && hp->h.deep < depth))
178 {
179 register header *np = hp->h.next;
180
181 free (hp); /* Collect garbage. */
182
183 hp = np; /* -> next header. */
184 }
185 else
186 break; /* Rest are not deeper. */
187
188 last_alloca_header = hp; /* -> last valid storage. */
189
190 # ifdef emacs
191 UNBLOCK_INPUT;
192 # endif
193 }
194
195 if (size == 0)
196 return NULL; /* No allocation required. */
197
198 /* Allocate combined header + user data storage. */
199
200 {
201 /* Address of header. */
202 register header *new;
203
204 size_t combined_size = sizeof (header) + size;
205 if (combined_size < sizeof (header))
206 memory_full ();
207
208 new = malloc (combined_size);
209
210 if (! new)
211 memory_full ();
212
213 new->h.next = last_alloca_header;
214 new->h.deep = depth;
215
216 last_alloca_header = new;
217
218 /* User storage begins just after header. */
219
220 return (void *) (new + 1);
221 }
222 }
223
224 # if defined (CRAY) && defined (CRAY_STACKSEG_END)
225
226 # ifdef DEBUG_I00AFUNC
227 # include <stdio.h>
228 # endif
229
230 # ifndef CRAY_STACK
231 # define CRAY_STACK
232 # ifndef CRAY2
233 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
234 struct stack_control_header
235 {
236 long shgrow:32; /* Number of times stack has grown. */
237 long shaseg:32; /* Size of increments to stack. */
238 long shhwm:32; /* High water mark of stack. */
239 long shsize:32; /* Current size of stack (all segments). */
240 };
241
242 /* The stack segment linkage control information occurs at
243 the high-address end of a stack segment. (The stack
244 grows from low addresses to high addresses.) The initial
245 part of the stack segment linkage control information is
246 0200 (octal) words. This provides for register storage
247 for the routine which overflows the stack. */
248
249 struct stack_segment_linkage
250 {
251 long ss[0200]; /* 0200 overflow words. */
252 long sssize:32; /* Number of words in this segment. */
253 long ssbase:32; /* Offset to stack base. */
254 long:32;
255 long sspseg:32; /* Offset to linkage control of previous
256 segment of stack. */
257 long:32;
258 long sstcpt:32; /* Pointer to task common address block. */
259 long sscsnm; /* Private control structure number for
260 microtasking. */
261 long ssusr1; /* Reserved for user. */
262 long ssusr2; /* Reserved for user. */
263 long sstpid; /* Process ID for pid based multi-tasking. */
264 long ssgvup; /* Pointer to multitasking thread giveup. */
265 long sscray[7]; /* Reserved for Cray Research. */
266 long ssa0;
267 long ssa1;
268 long ssa2;
269 long ssa3;
270 long ssa4;
271 long ssa5;
272 long ssa6;
273 long ssa7;
274 long sss0;
275 long sss1;
276 long sss2;
277 long sss3;
278 long sss4;
279 long sss5;
280 long sss6;
281 long sss7;
282 };
283
284 # else /* CRAY2 */
285 /* The following structure defines the vector of words
286 returned by the STKSTAT library routine. */
287 struct stk_stat
288 {
289 long now; /* Current total stack size. */
290 long maxc; /* Amount of contiguous space which would
291 be required to satisfy the maximum
292 stack demand to date. */
293 long high_water; /* Stack high-water mark. */
294 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
295 long hits; /* Number of internal buffer hits. */
296 long extends; /* Number of block extensions. */
297 long stko_mallocs; /* Block allocations by $STKOFEN. */
298 long underflows; /* Number of stack underflow calls ($STKRETN). */
299 long stko_free; /* Number of deallocations by $STKRETN. */
300 long stkm_free; /* Number of deallocations by $STKMRET. */
301 long segments; /* Current number of stack segments. */
302 long maxs; /* Maximum number of stack segments so far. */
303 long pad_size; /* Stack pad size. */
304 long current_address; /* Current stack segment address. */
305 long current_size; /* Current stack segment size. This
306 number is actually corrupted by STKSTAT to
307 include the fifteen word trailer area. */
308 long initial_address; /* Address of initial segment. */
309 long initial_size; /* Size of initial segment. */
310 };
311
312 /* The following structure describes the data structure which trails
313 any stack segment. I think that the description in 'asdef' is
314 out of date. I only describe the parts that I am sure about. */
315
316 struct stk_trailer
317 {
318 long this_address; /* Address of this block. */
319 long this_size; /* Size of this block (does not include
320 this trailer). */
321 long unknown2;
322 long unknown3;
323 long link; /* Address of trailer block of previous
324 segment. */
325 long unknown5;
326 long unknown6;
327 long unknown7;
328 long unknown8;
329 long unknown9;
330 long unknown10;
331 long unknown11;
332 long unknown12;
333 long unknown13;
334 long unknown14;
335 };
336
337 # endif /* CRAY2 */
338 # endif /* not CRAY_STACK */
339
340 # ifdef CRAY2
341 /* Determine a "stack measure" for an arbitrary ADDRESS.
342 I doubt that "lint" will like this much. */
343
344 static long
i00afunc(long * address)345 i00afunc (long *address)
346 {
347 struct stk_stat status;
348 struct stk_trailer *trailer;
349 long *block, size;
350 long result = 0;
351
352 /* We want to iterate through all of the segments. The first
353 step is to get the stack status structure. We could do this
354 more quickly and more directly, perhaps, by referencing the
355 $LM00 common block, but I know that this works. */
356
357 STKSTAT (&status);
358
359 /* Set up the iteration. */
360
361 trailer = (struct stk_trailer *) (status.current_address
362 + status.current_size
363 - 15);
364
365 /* There must be at least one stack segment. Therefore it is
366 a fatal error if "trailer" is null. */
367
368 if (trailer == 0)
369 abort ();
370
371 /* Discard segments that do not contain our argument address. */
372
373 while (trailer != 0)
374 {
375 block = (long *) trailer->this_address;
376 size = trailer->this_size;
377 if (block == 0 || size == 0)
378 abort ();
379 trailer = (struct stk_trailer *) trailer->link;
380 if ((block <= address) && (address < (block + size)))
381 break;
382 }
383
384 /* Set the result to the offset in this segment and add the sizes
385 of all predecessor segments. */
386
387 result = address - block;
388
389 if (trailer == 0)
390 {
391 return result;
392 }
393
394 do
395 {
396 if (trailer->this_size <= 0)
397 abort ();
398 result += trailer->this_size;
399 trailer = (struct stk_trailer *) trailer->link;
400 }
401 while (trailer != 0);
402
403 /* We are done. Note that if you present a bogus address (one
404 not in any segment), you will get a different number back, formed
405 from subtracting the address of the first block. This is probably
406 not what you want. */
407
408 return (result);
409 }
410
411 # else /* not CRAY2 */
412 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
413 Determine the number of the cell within the stack,
414 given the address of the cell. The purpose of this
415 routine is to linearize, in some sense, stack addresses
416 for alloca. */
417
418 static long
i00afunc(long address)419 i00afunc (long address)
420 {
421 long stkl = 0;
422
423 long size, pseg, this_segment, stack;
424 long result = 0;
425
426 struct stack_segment_linkage *ssptr;
427
428 /* Register B67 contains the address of the end of the
429 current stack segment. If you (as a subprogram) store
430 your registers on the stack and find that you are past
431 the contents of B67, you have overflowed the segment.
432
433 B67 also points to the stack segment linkage control
434 area, which is what we are really interested in. */
435
436 stkl = CRAY_STACKSEG_END ();
437 ssptr = (struct stack_segment_linkage *) stkl;
438
439 /* If one subtracts 'size' from the end of the segment,
440 one has the address of the first word of the segment.
441
442 If this is not the first segment, 'pseg' will be
443 nonzero. */
444
445 pseg = ssptr->sspseg;
446 size = ssptr->sssize;
447
448 this_segment = stkl - size;
449
450 /* It is possible that calling this routine itself caused
451 a stack overflow. Discard stack segments which do not
452 contain the target address. */
453
454 while (!(this_segment <= address && address <= stkl))
455 {
456 # ifdef DEBUG_I00AFUNC
457 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
458 # endif
459 if (pseg == 0)
460 break;
461 stkl = stkl - pseg;
462 ssptr = (struct stack_segment_linkage *) stkl;
463 size = ssptr->sssize;
464 pseg = ssptr->sspseg;
465 this_segment = stkl - size;
466 }
467
468 result = address - this_segment;
469
470 /* If you subtract pseg from the current end of the stack,
471 you get the address of the previous stack segment's end.
472 This seems a little convoluted to me, but I'll bet you save
473 a cycle somewhere. */
474
475 while (pseg != 0)
476 {
477 # ifdef DEBUG_I00AFUNC
478 fprintf (stderr, "%011o %011o\n", pseg, size);
479 # endif
480 stkl = stkl - pseg;
481 ssptr = (struct stack_segment_linkage *) stkl;
482 size = ssptr->sssize;
483 pseg = ssptr->sspseg;
484 result += size;
485 }
486 return (result);
487 }
488
489 # endif /* not CRAY2 */
490 # endif /* CRAY */
491
492 # endif /* no alloca */
493 #endif /* not GCC version 2 */
494