Updated from libc
[make.git] / alloca.c
blob7020f32c88232398fdcc691bc030958eea68c8d2
1 /* alloca.c -- allocate automatically reclaimed memory
2 (Mostly) portable public-domain implementation -- D A Gwyn
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.
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.
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.
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. */
24 #ifdef HAVE_CONFIG_H
25 #include <config.h>
26 #endif
28 #ifdef emacs
29 #include "blockinput.h"
30 #endif
32 /* If compiling with GCC 2, this file's not needed. */
33 #if !defined (__GNUC__) || __GNUC__ < 2
35 /* If someone has defined alloca as a macro,
36 there must be some other way alloca is supposed to work. */
37 #ifndef alloca
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
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 */
53 /* If your stack is a linked list of frames, you have to
54 provide an "address metric" ADDRESS_FUNCTION macro. */
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
63 #if __STDC__
64 typedef void *pointer;
65 #else
66 typedef char *pointer;
67 #endif
69 #define NULL 0
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.
77 Non-Emacs programs expect this to call use xmalloc.
79 Callers below should use malloc. */
81 #ifndef emacs
82 #define malloc xmalloc
83 #endif
84 extern pointer malloc ();
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.
90 STACK_DIRECTION > 0 => grows toward higher addresses
91 STACK_DIRECTION < 0 => grows toward lower addresses
92 STACK_DIRECTION = 0 => direction of growth unknown */
94 #ifndef STACK_DIRECTION
95 #define STACK_DIRECTION 0 /* Direction unknown. */
96 #endif
98 #if STACK_DIRECTION != 0
100 #define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
102 #else /* STACK_DIRECTION == 0; need run-time code. */
104 static int stack_dir; /* 1 or -1 once known. */
105 #define STACK_DIR stack_dir
107 static void
108 find_stack_direction ()
110 static char *addr = NULL; /* Address of first `dummy', once known. */
111 auto char dummy; /* To get stack address. */
113 if (addr == NULL)
114 { /* Initial entry. */
115 addr = ADDRESS_FUNCTION (dummy);
117 find_stack_direction (); /* Recurse once. */
119 else
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. */
129 #endif /* STACK_DIRECTION == 0 */
131 /* An "alloca header" is used to:
132 (a) chain together all alloca'ed blocks;
133 (b) keep track of stack depth.
135 It is very important that sizeof(header) agree with malloc
136 alignment chunk size. The following default should work okay. */
138 #ifndef ALIGN_SIZE
139 #define ALIGN_SIZE sizeof(double)
140 #endif
142 typedef union hdr
144 char align[ALIGN_SIZE]; /* To force sizeof(header). */
145 struct
147 union hdr *next; /* For chaining headers. */
148 char *deep; /* For stack depth measure. */
149 } h;
150 } header;
152 static header *last_alloca_header = NULL; /* -> last alloca header. */
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. */
161 pointer
162 alloca (size)
163 unsigned size;
165 auto char probe; /* Probes stack depth: */
166 register char *depth = ADDRESS_FUNCTION (probe);
168 #if STACK_DIRECTION == 0
169 if (STACK_DIR == 0) /* Unknown growth direction. */
170 find_stack_direction ();
171 #endif
173 /* Reclaim garbage, defined as all alloca'd storage that
174 was allocated from deeper in the stack than currently. */
177 register header *hp; /* Traverses linked list. */
179 #ifdef emacs
180 BLOCK_INPUT;
181 #endif
183 for (hp = last_alloca_header; hp != NULL;)
184 if ((STACK_DIR > 0 && hp->h.deep > depth)
185 || (STACK_DIR < 0 && hp->h.deep < depth))
187 register header *np = hp->h.next;
189 free ((pointer) hp); /* Collect garbage. */
191 hp = np; /* -> next header. */
193 else
194 break; /* Rest are not deeper. */
196 last_alloca_header = hp; /* -> last valid storage. */
198 #ifdef emacs
199 UNBLOCK_INPUT;
200 #endif
203 if (size == 0)
204 return NULL; /* No allocation required. */
206 /* Allocate combined header + user data storage. */
209 register pointer new = malloc (sizeof (header) + size);
210 /* Address of header. */
212 ((header *) new)->h.next = last_alloca_header;
213 ((header *) new)->h.deep = depth;
215 last_alloca_header = (header *) new;
217 /* User storage begins just after header. */
219 return (pointer) ((char *) new + sizeof (header));
223 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
225 #ifdef DEBUG_I00AFUNC
226 #include <stdio.h>
227 #endif
229 #ifndef CRAY_STACK
230 #define CRAY_STACK
231 #ifndef CRAY2
232 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
233 struct stack_control_header
235 long shgrow:32; /* Number of times stack has grown. */
236 long shaseg:32; /* Size of increments to stack. */
237 long shhwm:32; /* High water mark of stack. */
238 long shsize:32; /* Current size of stack (all segments). */
241 /* The stack segment linkage control information occurs at
242 the high-address end of a stack segment. (The stack
243 grows from low addresses to high addresses.) The initial
244 part of the stack segment linkage control information is
245 0200 (octal) words. This provides for register storage
246 for the routine which overflows the stack. */
248 struct stack_segment_linkage
250 long ss[0200]; /* 0200 overflow words. */
251 long sssize:32; /* Number of words in this segment. */
252 long ssbase:32; /* Offset to stack base. */
253 long:32;
254 long sspseg:32; /* Offset to linkage control of previous
255 segment of stack. */
256 long:32;
257 long sstcpt:32; /* Pointer to task common address block. */
258 long sscsnm; /* Private control structure number for
259 microtasking. */
260 long ssusr1; /* Reserved for user. */
261 long ssusr2; /* Reserved for user. */
262 long sstpid; /* Process ID for pid based multi-tasking. */
263 long ssgvup; /* Pointer to multitasking thread giveup. */
264 long sscray[7]; /* Reserved for Cray Research. */
265 long ssa0;
266 long ssa1;
267 long ssa2;
268 long ssa3;
269 long ssa4;
270 long ssa5;
271 long ssa6;
272 long ssa7;
273 long sss0;
274 long sss1;
275 long sss2;
276 long sss3;
277 long sss4;
278 long sss5;
279 long sss6;
280 long sss7;
283 #else /* CRAY2 */
284 /* The following structure defines the vector of words
285 returned by the STKSTAT library routine. */
286 struct stk_stat
288 long now; /* Current total stack size. */
289 long maxc; /* Amount of contiguous space which would
290 be required to satisfy the maximum
291 stack demand to date. */
292 long high_water; /* Stack high-water mark. */
293 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
294 long hits; /* Number of internal buffer hits. */
295 long extends; /* Number of block extensions. */
296 long stko_mallocs; /* Block allocations by $STKOFEN. */
297 long underflows; /* Number of stack underflow calls ($STKRETN). */
298 long stko_free; /* Number of deallocations by $STKRETN. */
299 long stkm_free; /* Number of deallocations by $STKMRET. */
300 long segments; /* Current number of stack segments. */
301 long maxs; /* Maximum number of stack segments so far. */
302 long pad_size; /* Stack pad size. */
303 long current_address; /* Current stack segment address. */
304 long current_size; /* Current stack segment size. This
305 number is actually corrupted by STKSTAT to
306 include the fifteen word trailer area. */
307 long initial_address; /* Address of initial segment. */
308 long initial_size; /* Size of initial segment. */
311 /* The following structure describes the data structure which trails
312 any stack segment. I think that the description in 'asdef' is
313 out of date. I only describe the parts that I am sure about. */
315 struct stk_trailer
317 long this_address; /* Address of this block. */
318 long this_size; /* Size of this block (does not include
319 this trailer). */
320 long unknown2;
321 long unknown3;
322 long link; /* Address of trailer block of previous
323 segment. */
324 long unknown5;
325 long unknown6;
326 long unknown7;
327 long unknown8;
328 long unknown9;
329 long unknown10;
330 long unknown11;
331 long unknown12;
332 long unknown13;
333 long unknown14;
336 #endif /* CRAY2 */
337 #endif /* not CRAY_STACK */
339 #ifdef CRAY2
340 /* Determine a "stack measure" for an arbitrary ADDRESS.
341 I doubt that "lint" will like this much. */
343 static long
344 i00afunc (long *address)
346 struct stk_stat status;
347 struct stk_trailer *trailer;
348 long *block, size;
349 long result = 0;
351 /* We want to iterate through all of the segments. The first
352 step is to get the stack status structure. We could do this
353 more quickly and more directly, perhaps, by referencing the
354 $LM00 common block, but I know that this works. */
356 STKSTAT (&status);
358 /* Set up the iteration. */
360 trailer = (struct stk_trailer *) (status.current_address
361 + status.current_size
362 - 15);
364 /* There must be at least one stack segment. Therefore it is
365 a fatal error if "trailer" is null. */
367 if (trailer == 0)
368 abort ();
370 /* Discard segments that do not contain our argument address. */
372 while (trailer != 0)
374 block = (long *) trailer->this_address;
375 size = trailer->this_size;
376 if (block == 0 || size == 0)
377 abort ();
378 trailer = (struct stk_trailer *) trailer->link;
379 if ((block <= address) && (address < (block + size)))
380 break;
383 /* Set the result to the offset in this segment and add the sizes
384 of all predecessor segments. */
386 result = address - block;
388 if (trailer == 0)
390 return result;
395 if (trailer->this_size <= 0)
396 abort ();
397 result += trailer->this_size;
398 trailer = (struct stk_trailer *) trailer->link;
400 while (trailer != 0);
402 /* We are done. Note that if you present a bogus address (one
403 not in any segment), you will get a different number back, formed
404 from subtracting the address of the first block. This is probably
405 not what you want. */
407 return (result);
410 #else /* not CRAY2 */
411 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
412 Determine the number of the cell within the stack,
413 given the address of the cell. The purpose of this
414 routine is to linearize, in some sense, stack addresses
415 for alloca. */
417 static long
418 i00afunc (long address)
420 long stkl = 0;
422 long size, pseg, this_segment, stack;
423 long result = 0;
425 struct stack_segment_linkage *ssptr;
427 /* Register B67 contains the address of the end of the
428 current stack segment. If you (as a subprogram) store
429 your registers on the stack and find that you are past
430 the contents of B67, you have overflowed the segment.
432 B67 also points to the stack segment linkage control
433 area, which is what we are really interested in. */
435 stkl = CRAY_STACKSEG_END ();
436 ssptr = (struct stack_segment_linkage *) stkl;
438 /* If one subtracts 'size' from the end of the segment,
439 one has the address of the first word of the segment.
441 If this is not the first segment, 'pseg' will be
442 nonzero. */
444 pseg = ssptr->sspseg;
445 size = ssptr->sssize;
447 this_segment = stkl - size;
449 /* It is possible that calling this routine itself caused
450 a stack overflow. Discard stack segments which do not
451 contain the target address. */
453 while (!(this_segment <= address && address <= stkl))
455 #ifdef DEBUG_I00AFUNC
456 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
457 #endif
458 if (pseg == 0)
459 break;
460 stkl = stkl - pseg;
461 ssptr = (struct stack_segment_linkage *) stkl;
462 size = ssptr->sssize;
463 pseg = ssptr->sspseg;
464 this_segment = stkl - size;
467 result = address - this_segment;
469 /* If you subtract pseg from the current end of the stack,
470 you get the address of the previous stack segment's end.
471 This seems a little convoluted to me, but I'll bet you save
472 a cycle somewhere. */
474 while (pseg != 0)
476 #ifdef DEBUG_I00AFUNC
477 fprintf (stderr, "%011o %011o\n", pseg, size);
478 #endif
479 stkl = stkl - pseg;
480 ssptr = (struct stack_segment_linkage *) stkl;
481 size = ssptr->sssize;
482 pseg = ssptr->sspseg;
483 result += size;
485 return (result);
488 #endif /* not CRAY2 */
489 #endif /* CRAY */
491 #endif /* no alloca */
492 #endif /* not GCC version 2 */