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