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 /* Synched up with: FSF 19.30. */
29 Very few changes for XEmacs.
36 /* XEmacs: If compiling with GCC 2, this file is theoretically not needed.
37 However, alloca() is broken under GCC 2 on many machines: you
38 cannot put a call to alloca() as part of an argument to a function.
40 /* If someone has defined alloca as a macro,
41 there must be some other way alloca is supposed to work. */
42 /* XEmacs sometimes uses the C alloca even when a builtin alloca is available,
43 because it's safer. */
44 #if defined (EMACS_WANTS_C_ALLOCA) || (!defined (alloca) && (!defined (__GNUC__) || __GNUC__ < 2))
48 /* actually, only want this if static is defined as ""
49 -- this is for usg, in which emacs must undefine static
50 in order to make unexec workable
52 #ifndef STACK_DIRECTION
53 you lose-- must know STACK_DIRECTION at compile - time
54 #endif /* STACK_DIRECTION undefined */
57 /* If your stack is a linked list of frames, you have to
58 provide an "address metric" ADDRESS_FUNCTION macro. */
59 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
61 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
63 #define ADDRESS_FUNCTION(arg) &(arg)
65 #ifdef __STDC__ /* XEmacs change */
66 typedef void *pointer;
68 typedef char *pointer;
71 /* XEmacs: With ERROR_CHECK_MALLOC defined, there is no xfree -- it's
72 a macro that does some stuff to try and trap invalid frees,
73 and then calls xfree_1 to actually do the work. */
76 # ifdef ERROR_CHECK_MALLOC
77 void xfree_1(pointer);
78 # define xfree xfree_1
88 /* Different portions of Emacs need to call different versions of
89 malloc. The Emacs executable needs alloca to call xmalloc, because
90 ordinary malloc isn't protected from input signals. On the other
91 hand, the utilities in lib-src need alloca to call malloc; some of
92 them are very simple, and don't have an xmalloc routine.
94 Non-Emacs programs expect this to call use xmalloc.
96 Callers below should use malloc. */
99 #define malloc xmalloc
101 extern pointer malloc();
103 /* Define STACK_DIRECTION if you know the direction of stack
104 growth for your system; otherwise it will be automatically
107 STACK_DIRECTION > 0 => grows toward higher addresses
108 STACK_DIRECTION < 0 => grows toward lower addresses
109 STACK_DIRECTION = 0 => direction of growth unknown */
111 #ifndef STACK_DIRECTION
112 #define STACK_DIRECTION 0 /* Direction unknown. */
115 #if STACK_DIRECTION != 0
117 #define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
119 #else /* STACK_DIRECTION == 0; need run-time code. */
121 static int stack_dir; /* 1 or -1 once known. */
122 #define STACK_DIR stack_dir
124 static void find_stack_direction()
126 static char *addr = NULL; /* Address of first `dummy', once known. */
127 auto char dummy; /* To get stack address. */
129 if (addr == NULL) { /* Initial entry. */
130 addr = ADDRESS_FUNCTION(dummy);
132 find_stack_direction(); /* Recurse once. */
135 if (ADDRESS_FUNCTION(dummy) > addr)
136 stack_dir = 1; /* Stack grew upward. */
138 stack_dir = -1; /* Stack grew downward. */
142 #endif /* STACK_DIRECTION == 0 */
144 /* An "alloca header" is used to:
145 (a) chain together all alloca'ed blocks;
146 (b) keep track of stack depth.
148 It is very important that sizeof(header) agree with malloc
149 alignment chunk size. The following default should work okay. */
152 #define ALIGN_SIZE sizeof(double)
156 char align[ALIGN_SIZE]; /* To force sizeof(header). */
158 union hdr *next; /* For chaining headers. */
159 char *deep; /* For stack depth measure. */
163 static header *last_alloca_header = NULL; /* -> last alloca header. */
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. */
173 #ifdef EMACS_WANTS_C_ALLOCA
180 auto char probe; /* Probes stack depth: */
181 register char *depth = ADDRESS_FUNCTION(probe);
183 #if STACK_DIRECTION == 0
184 if (STACK_DIR == 0) /* Unknown growth direction. */
185 find_stack_direction();
188 /* Reclaim garbage, defined as all alloca'd storage that
189 was allocated from deeper in the stack than currently. */
192 register header *hp; /* Traverses linked list. */
194 for (hp = last_alloca_header; hp != NULL;)
195 if ((STACK_DIR > 0 && hp->h.deep > depth)
196 || (STACK_DIR < 0 && hp->h.deep < depth)) {
197 register header *np = hp->h.next;
199 free((pointer) hp); /* Collect garbage. */
201 hp = np; /* -> next header. */
203 break; /* Rest are not deeper. */
205 last_alloca_header = hp; /* -> last valid storage. */
209 return NULL; /* No allocation required. */
211 /* Allocate combined header + user data storage. */
214 register pointer new = malloc(sizeof(header) + size);
215 /* Address of header. */
217 ((header *) new)->h.next = last_alloca_header;
218 ((header *) new)->h.deep = depth;
220 last_alloca_header = (header *) new;
222 /* User storage begins just after header. */
224 return (pointer) ((char *)new + sizeof(header));
228 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
230 #ifdef DEBUG_I00AFUNC
237 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
238 struct stack_control_header {
239 long shgrow:32; /* Number of times stack has grown. */
240 long shaseg:32; /* Size of increments to stack. */
241 long shhwm:32; /* High water mark of stack. */
242 long shsize:32; /* Current size of stack (all segments). */
245 /* The stack segment linkage control information occurs at
246 the high-address end of a stack segment. (The stack
247 grows from low addresses to high addresses.) The initial
248 part of the stack segment linkage control information is
249 0200 (octal) words. This provides for register storage
250 for the routine which overflows the stack. */
252 struct stack_segment_linkage {
253 long ss[0200]; /* 0200 overflow words. */
254 long sssize:32; /* Number of words in this segment. */
255 long ssbase:32; /* Offset to stack base. */
257 long sspseg:32; /* Offset to linkage control of previous
260 long sstcpt:32; /* Pointer to task common address block. */
261 long sscsnm; /* Private control structure number for
263 long ssusr1; /* Reserved for user. */
264 long ssusr2; /* Reserved for user. */
265 long sstpid; /* Process ID for pid based multi-tasking. */
266 long ssgvup; /* Pointer to multitasking thread giveup. */
267 long sscray[7]; /* Reserved for Cray Research. */
287 /* The following structure defines the vector of words
288 returned by the STKSTAT library routine. */
290 long now; /* Current total stack size. */
291 long maxc; /* Amount of contiguous space which would
292 be required to satisfy the maximum
293 stack demand to date. */
294 long high_water; /* Stack high-water mark. */
295 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
296 long hits; /* Number of internal buffer hits. */
297 long extends; /* Number of block extensions. */
298 long stko_mallocs; /* Block allocations by $STKOFEN. */
299 long underflows; /* Number of stack underflow calls ($STKRETN). */
300 long stko_free; /* Number of deallocations by $STKRETN. */
301 long stkm_free; /* Number of deallocations by $STKMRET. */
302 long segments; /* Current number of stack segments. */
303 long maxs; /* Maximum number of stack segments so far. */
304 long pad_size; /* Stack pad size. */
305 long current_address; /* Current stack segment address. */
306 long current_size; /* Current stack segment size. This
307 number is actually corrupted by STKSTAT to
308 include the fifteen word trailer area. */
309 long initial_address; /* Address of initial segment. */
310 long initial_size; /* Size of initial segment. */
313 /* The following structure describes the data structure which trails
314 any stack segment. I think that the description in 'asdef' is
315 out of date. I only describe the parts that I am sure about. */
318 long this_address; /* Address of this block. */
319 long this_size; /* Size of this block (does not include
323 long link; /* Address of trailer block of previous
338 #endif /* not CRAY_STACK */
341 /* Determine a "stack measure" for an arbitrary ADDRESS.
342 I doubt that "lint" will like this much. */
344 static long i00afunc(long *address)
346 struct stk_stat status;
347 struct stk_trailer *trailer;
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. */
358 /* Set up the iteration. */
360 trailer = (struct stk_trailer *)(status.current_address
361 + status.current_size - 15);
363 /* There must be at least one stack segment. Therefore it is
364 a fatal error if "trailer" is null. */
369 /* Discard segments that do not contain our argument address. */
371 while (trailer != 0) {
372 block = (long *)trailer->this_address;
373 size = trailer->this_size;
374 if (block == 0 || size == 0)
376 trailer = (struct stk_trailer *)trailer->link;
377 if ((block <= address) && (address < (block + size)))
381 /* Set the result to the offset in this segment and add the sizes
382 of all predecessor segments. */
384 result = address - block;
391 if (trailer->this_size <= 0)
393 result += trailer->this_size;
394 trailer = (struct stk_trailer *)trailer->link;
396 while (trailer != 0);
398 /* We are done. Note that if you present a bogus address (one
399 not in any segment), you will get a different number back, formed
400 from subtracting the address of the first block. This is probably
401 not what you want. */
406 #else /* not CRAY2 */
407 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
408 Determine the number of the cell within the stack,
409 given the address of the cell. The purpose of this
410 routine is to linearize, in some sense, stack addresses
413 static long i00afunc(long address)
417 long size, pseg, this_segment, stack;
420 struct stack_segment_linkage *ssptr;
422 /* Register B67 contains the address of the end of the
423 current stack segment. If you (as a subprogram) store
424 your registers on the stack and find that you are past
425 the contents of B67, you have overflowed the segment.
427 B67 also points to the stack segment linkage control
428 area, which is what we are really interested in. */
430 stkl = CRAY_STACKSEG_END();
431 ssptr = (struct stack_segment_linkage *)stkl;
433 /* If one subtracts 'size' from the end of the segment,
434 one has the address of the first word of the segment.
436 If this is not the first segment, 'pseg' will be
439 pseg = ssptr->sspseg;
440 size = ssptr->sssize;
442 this_segment = stkl - size;
444 /* It is possible that calling this routine itself caused
445 a stack overflow. Discard stack segments which do not
446 contain the target address. */
448 while (!(this_segment <= address && address <= stkl)) {
449 #ifdef DEBUG_I00AFUNC
450 fprintf(stderr, "%011o %011o %011o\n", this_segment, address,
456 ssptr = (struct stack_segment_linkage *)stkl;
457 size = ssptr->sssize;
458 pseg = ssptr->sspseg;
459 this_segment = stkl - size;
462 result = address - this_segment;
464 /* If you subtract pseg from the current end of the stack,
465 you get the address of the previous stack segment's end.
466 This seems a little convoluted to me, but I'll bet you save
467 a cycle somewhere. */
470 #ifdef DEBUG_I00AFUNC
471 fprintf(stderr, "%011o %011o\n", pseg, size);
474 ssptr = (struct stack_segment_linkage *)stkl;
475 size = ssptr->sssize;
476 pseg = ssptr->sspseg;
482 #endif /* not CRAY2 */
485 #endif /* complicated expression at top of file */