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. */
36 #include "blockinput.h"
39 /* If compiling with GCC 2, this file's not needed. */
40 #if !defined (__GNUC__) || __GNUC__ < 2
42 /* If someone has defined alloca as a macro,
43 there must be some other way alloca is supposed to work. */
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
55 -- must know STACK_DIRECTION at compile-time
56 #endif /* STACK_DIRECTION undefined */
60 /* If your stack is a linked list of frames, you have to
61 provide an "address metric" ADDRESS_FUNCTION macro. */
63 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
65 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
67 #define ADDRESS_FUNCTION(arg) &(arg)
71 typedef void *pointer;
73 typedef char *pointer;
78 /* Different portions of Emacs need to call different versions of
79 malloc. The Emacs executable needs alloca to call xmalloc, because
80 ordinary malloc isn't protected from input signals. On the other
81 hand, the utilities in lib-src need alloca to call malloc; some of
82 them are very simple, and don't have an xmalloc routine.
84 Non-Emacs programs expect this to call use xmalloc.
86 Callers below should use malloc. */
89 #define malloc xmalloc
91 extern pointer malloc ();
93 /* Define STACK_DIRECTION if you know the direction of stack
94 growth for your system; otherwise it will be automatically
97 STACK_DIRECTION > 0 => grows toward higher addresses
98 STACK_DIRECTION < 0 => grows toward lower addresses
99 STACK_DIRECTION = 0 => direction of growth unknown */
101 #ifndef STACK_DIRECTION
102 #define STACK_DIRECTION 0 /* Direction unknown. */
105 #if STACK_DIRECTION != 0
107 #define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
109 #else /* STACK_DIRECTION == 0; need run-time code. */
111 static int stack_dir; /* 1 or -1 once known. */
112 #define STACK_DIR stack_dir
115 find_stack_direction ()
117 static char *addr = NULL; /* Address of first `dummy', once known. */
118 auto char dummy; /* To get stack address. */
121 { /* Initial entry. */
122 addr = ADDRESS_FUNCTION (dummy);
124 find_stack_direction (); /* Recurse once. */
129 if (ADDRESS_FUNCTION (dummy) > addr)
130 stack_dir = 1; /* Stack grew upward. */
132 stack_dir = -1; /* Stack grew downward. */
136 #endif /* STACK_DIRECTION == 0 */
138 /* An "alloca header" is used to:
139 (a) chain together all alloca'ed blocks;
140 (b) keep track of stack depth.
142 It is very important that sizeof(header) agree with malloc
143 alignment chunk size. The following default should work okay. */
146 #define ALIGN_SIZE sizeof(double)
151 char align[ALIGN_SIZE]; /* To force sizeof(header). */
154 union hdr *next; /* For chaining headers. */
155 char *deep; /* For stack depth measure. */
159 static header *last_alloca_header = NULL; /* -> last alloca header. */
161 /* Return a pointer to at least SIZE bytes of storage,
162 which will be automatically reclaimed upon exit from
163 the procedure that called alloca. Originally, this space
164 was supposed to be taken from the current stack frame of the
165 caller, but that method cannot be made to work for some
166 implementations of C, for example under Gould's UTX/32. */
172 auto char probe; /* Probes stack depth: */
173 register char *depth = ADDRESS_FUNCTION (probe);
175 #if STACK_DIRECTION == 0
176 if (STACK_DIR == 0) /* Unknown growth direction. */
177 find_stack_direction ();
180 /* Reclaim garbage, defined as all alloca'd storage that
181 was allocated from deeper in the stack than currently. */
184 register header *hp; /* Traverses linked list. */
190 for (hp = last_alloca_header; hp != NULL;)
191 if ((STACK_DIR > 0 && hp->h.deep > depth)
192 || (STACK_DIR < 0 && hp->h.deep < depth))
194 register header *np = hp->h.next;
196 free ((pointer) hp); /* Collect garbage. */
198 hp = np; /* -> next header. */
201 break; /* Rest are not deeper. */
203 last_alloca_header = hp; /* -> last valid storage. */
211 return NULL; /* No allocation required. */
213 /* Allocate combined header + user data storage. */
216 register pointer new = malloc (sizeof (header) + size);
217 /* Address of header. */
222 ((header *) new)->h.next = last_alloca_header;
223 ((header *) new)->h.deep = depth;
225 last_alloca_header = (header *) new;
227 /* User storage begins just after header. */
229 return (pointer) ((char *) new + sizeof (header));
233 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
235 #ifdef DEBUG_I00AFUNC
242 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
243 struct stack_control_header
245 long shgrow:32; /* Number of times stack has grown. */
246 long shaseg:32; /* Size of increments to stack. */
247 long shhwm:32; /* High water mark of stack. */
248 long shsize:32; /* Current size of stack (all segments). */
251 /* The stack segment linkage control information occurs at
252 the high-address end of a stack segment. (The stack
253 grows from low addresses to high addresses.) The initial
254 part of the stack segment linkage control information is
255 0200 (octal) words. This provides for register storage
256 for the routine which overflows the stack. */
258 struct stack_segment_linkage
260 long ss[0200]; /* 0200 overflow words. */
261 long sssize:32; /* Number of words in this segment. */
262 long ssbase:32; /* Offset to stack base. */
264 long sspseg:32; /* Offset to linkage control of previous
267 long sstcpt:32; /* Pointer to task common address block. */
268 long sscsnm; /* Private control structure number for
270 long ssusr1; /* Reserved for user. */
271 long ssusr2; /* Reserved for user. */
272 long sstpid; /* Process ID for pid based multi-tasking. */
273 long ssgvup; /* Pointer to multitasking thread giveup. */
274 long sscray[7]; /* Reserved for Cray Research. */
294 /* The following structure defines the vector of words
295 returned by the STKSTAT library routine. */
298 long now; /* Current total stack size. */
299 long maxc; /* Amount of contiguous space which would
300 be required to satisfy the maximum
301 stack demand to date. */
302 long high_water; /* Stack high-water mark. */
303 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
304 long hits; /* Number of internal buffer hits. */
305 long extends; /* Number of block extensions. */
306 long stko_mallocs; /* Block allocations by $STKOFEN. */
307 long underflows; /* Number of stack underflow calls ($STKRETN). */
308 long stko_free; /* Number of deallocations by $STKRETN. */
309 long stkm_free; /* Number of deallocations by $STKMRET. */
310 long segments; /* Current number of stack segments. */
311 long maxs; /* Maximum number of stack segments so far. */
312 long pad_size; /* Stack pad size. */
313 long current_address; /* Current stack segment address. */
314 long current_size; /* Current stack segment size. This
315 number is actually corrupted by STKSTAT to
316 include the fifteen word trailer area. */
317 long initial_address; /* Address of initial segment. */
318 long initial_size; /* Size of initial segment. */
321 /* The following structure describes the data structure which trails
322 any stack segment. I think that the description in 'asdef' is
323 out of date. I only describe the parts that I am sure about. */
327 long this_address; /* Address of this block. */
328 long this_size; /* Size of this block (does not include
332 long link; /* Address of trailer block of previous
347 #endif /* not CRAY_STACK */
350 /* Determine a "stack measure" for an arbitrary ADDRESS.
351 I doubt that "lint" will like this much. */
354 i00afunc (long *address)
356 struct stk_stat status;
357 struct stk_trailer *trailer;
361 /* We want to iterate through all of the segments. The first
362 step is to get the stack status structure. We could do this
363 more quickly and more directly, perhaps, by referencing the
364 $LM00 common block, but I know that this works. */
368 /* Set up the iteration. */
370 trailer = (struct stk_trailer *) (status.current_address
371 + status.current_size
374 /* There must be at least one stack segment. Therefore it is
375 a fatal error if "trailer" is null. */
380 /* Discard segments that do not contain our argument address. */
384 block = (long *) trailer->this_address;
385 size = trailer->this_size;
386 if (block == 0 || size == 0)
388 trailer = (struct stk_trailer *) trailer->link;
389 if ((block <= address) && (address < (block + size)))
393 /* Set the result to the offset in this segment and add the sizes
394 of all predecessor segments. */
396 result = address - block;
405 if (trailer->this_size <= 0)
407 result += trailer->this_size;
408 trailer = (struct stk_trailer *) trailer->link;
410 while (trailer != 0);
412 /* We are done. Note that if you present a bogus address (one
413 not in any segment), you will get a different number back, formed
414 from subtracting the address of the first block. This is probably
415 not what you want. */
420 #else /* not CRAY2 */
421 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
422 Determine the number of the cell within the stack,
423 given the address of the cell. The purpose of this
424 routine is to linearize, in some sense, stack addresses
428 i00afunc (long address)
432 long size, pseg, this_segment, stack;
435 struct stack_segment_linkage *ssptr;
437 /* Register B67 contains the address of the end of the
438 current stack segment. If you (as a subprogram) store
439 your registers on the stack and find that you are past
440 the contents of B67, you have overflowed the segment.
442 B67 also points to the stack segment linkage control
443 area, which is what we are really interested in. */
445 stkl = CRAY_STACKSEG_END ();
446 ssptr = (struct stack_segment_linkage *) stkl;
448 /* If one subtracts 'size' from the end of the segment,
449 one has the address of the first word of the segment.
451 If this is not the first segment, 'pseg' will be
454 pseg = ssptr->sspseg;
455 size = ssptr->sssize;
457 this_segment = stkl - size;
459 /* It is possible that calling this routine itself caused
460 a stack overflow. Discard stack segments which do not
461 contain the target address. */
463 while (!(this_segment <= address && address <= stkl))
465 #ifdef DEBUG_I00AFUNC
466 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
471 ssptr = (struct stack_segment_linkage *) stkl;
472 size = ssptr->sssize;
473 pseg = ssptr->sspseg;
474 this_segment = stkl - size;
477 result = address - this_segment;
479 /* If you subtract pseg from the current end of the stack,
480 you get the address of the previous stack segment's end.
481 This seems a little convoluted to me, but I'll bet you save
482 a cycle somewhere. */
486 #ifdef DEBUG_I00AFUNC
487 fprintf (stderr, "%011o %011o\n", pseg, size);
490 ssptr = (struct stack_segment_linkage *) stkl;
491 size = ssptr->sssize;
492 pseg = ssptr->sspseg;
498 #endif /* not CRAY2 */
501 #endif /* no alloca */
502 #endif /* not GCC version 2 */