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