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. */
28 /* If compiling with GCC, this file's not needed. */
33 /* actually, only want this if static is defined as ""
34 -- this is for usg, in which emacs must undefine static
35 in order to make unexec workable
37 #ifndef STACK_DIRECTION
40 -- must know STACK_DIRECTION at compile-time
41 #endif /* STACK_DIRECTION undefined */
45 /* If your stack is a linked list of frames, you have to
46 provide an "address metric" ADDRESS_FUNCTION macro. */
48 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
50 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
52 #define ADDRESS_FUNCTION(arg) &(arg)
56 typedef void *pointer;
58 typedef char *pointer;
63 /* Different portions of Emacs need to call different versions of
64 malloc. The Emacs executable needs alloca to call xmalloc, because
65 ordinary malloc isn't protected from input signals. On the other
66 hand, the utilities in lib-src need alloca to call malloc; some of
67 them are very simple, and don't have an xmalloc routine.
69 Non-Emacs programs expect this to call use xmalloc.
71 Callers below should use malloc. */
75 #define malloc xmalloc
76 extern pointer xmalloc ();
82 void *p=(void *)malloc(s);
84 const char *meld="out of memory in alloca\n";
85 write(2,meld,strlen(meld));
90 #define malloc xmalloc
94 /* Define STACK_DIRECTION if you know the direction of stack
95 growth for your system; otherwise it will be automatically
98 STACK_DIRECTION > 0 => grows toward higher addresses
99 STACK_DIRECTION < 0 => grows toward lower addresses
100 STACK_DIRECTION = 0 => direction of growth unknown */
102 #ifndef STACK_DIRECTION
103 #define STACK_DIRECTION 0 /* Direction unknown. */
106 #if STACK_DIRECTION != 0
108 #define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
110 #else /* STACK_DIRECTION == 0; need run-time code. */
112 static int stack_dir; /* 1 or -1 once known. */
113 #define STACK_DIR stack_dir
116 find_stack_direction ()
118 static char *addr = NULL; /* Address of first `dummy', once known. */
119 auto char dummy; /* To get stack address. */
122 { /* Initial entry. */
123 addr = ADDRESS_FUNCTION (dummy);
125 find_stack_direction (); /* Recurse once. */
130 if (ADDRESS_FUNCTION (dummy) > addr)
131 stack_dir = 1; /* Stack grew upward. */
133 stack_dir = -1; /* Stack grew downward. */
137 #endif /* STACK_DIRECTION == 0 */
139 /* An "alloca header" is used to:
140 (a) chain together all alloca'ed blocks;
141 (b) keep track of stack depth.
143 It is very important that sizeof(header) agree with malloc
144 alignment chunk size. The following default should work okay. */
147 #define ALIGN_SIZE sizeof(double)
152 char align[ALIGN_SIZE]; /* To force sizeof(header). */
155 union hdr *next; /* For chaining headers. */
156 char *deep; /* For stack depth measure. */
160 static header *last_alloca_header = NULL; /* -> last alloca header. */
163 /* Return a pointer to at least SIZE bytes of storage,
164 which will be automatically reclaimed upon exit from
165 the procedure that called alloca. Originally, this space
166 was supposed to be taken from the current stack frame of the
167 caller, but that method cannot be made to work for some
168 implementations of C, for example under Gould's UTX/32. */
174 auto char probe; /* Probes stack depth: */
175 register char *depth = ADDRESS_FUNCTION (probe);
177 #if STACK_DIRECTION == 0
178 if (STACK_DIR == 0) /* Unknown growth direction. */
179 find_stack_direction ();
182 /* Reclaim garbage, defined as all alloca'd storage that
183 was allocated from deeper in the stack than currently. */
186 register header *hp; /* Traverses linked list. */
188 for (hp = last_alloca_header; hp != NULL;)
189 if ((STACK_DIR > 0 && hp->h.deep > depth)
190 || (STACK_DIR < 0 && hp->h.deep < depth))
192 register header *np = hp->h.next;
194 free ((pointer) hp); /* Collect garbage. */
196 hp = np; /* -> next header. */
199 break; /* Rest are not deeper. */
201 last_alloca_header = hp; /* -> last valid storage. */
205 return NULL; /* No allocation required. */
207 /* Allocate combined header + user data storage. */
210 register pointer new = malloc (sizeof (header) + size);
211 /* Address of header. */
213 ((header *) new)->h.next = last_alloca_header;
214 ((header *) new)->h.deep = depth;
216 last_alloca_header = (header *) new;
218 /* User storage begins just after header. */
220 return (pointer) ((char *) new + sizeof (header));
224 /* brute force hack around glibc-2.0.4 together with lcc
225 (need -D_BSD_SOURCE for u_long, but then get "alloca.h",
226 which #defines alloca to be __alloca). -- uwe
228 pointer __alloca (size) unsigned size;
229 { return alloca(size); }
231 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
233 #ifdef DEBUG_I00AFUNC
240 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
241 struct stack_control_header
243 long shgrow:32; /* Number of times stack has grown. */
244 long shaseg:32; /* Size of increments to stack. */
245 long shhwm:32; /* High water mark of stack. */
246 long shsize:32; /* Current size of stack (all segments). */
249 /* The stack segment linkage control information occurs at
250 the high-address end of a stack segment. (The stack
251 grows from low addresses to high addresses.) The initial
252 part of the stack segment linkage control information is
253 0200 (octal) words. This provides for register storage
254 for the routine which overflows the stack. */
256 struct stack_segment_linkage
258 long ss[0200]; /* 0200 overflow words. */
259 long sssize:32; /* Number of words in this segment. */
260 long ssbase:32; /* Offset to stack base. */
262 long sspseg:32; /* Offset to linkage control of previous
265 long sstcpt:32; /* Pointer to task common address block. */
266 long sscsnm; /* Private control structure number for
268 long ssusr1; /* Reserved for user. */
269 long ssusr2; /* Reserved for user. */
270 long sstpid; /* Process ID for pid based multi-tasking. */
271 long ssgvup; /* Pointer to multitasking thread giveup. */
272 long sscray[7]; /* Reserved for Cray Research. */
292 /* The following structure defines the vector of words
293 returned by the STKSTAT library routine. */
296 long now; /* Current total stack size. */
297 long maxc; /* Amount of contiguous space which would
298 be required to satisfy the maximum
299 stack demand to date. */
300 long high_water; /* Stack high-water mark. */
301 long overflows; /* Number of stack overflow ($STKOFEN) calls. */
302 long hits; /* Number of internal buffer hits. */
303 long extends; /* Number of block extensions. */
304 long stko_mallocs; /* Block allocations by $STKOFEN. */
305 long underflows; /* Number of stack underflow calls ($STKRETN). */
306 long stko_free; /* Number of deallocations by $STKRETN. */
307 long stkm_free; /* Number of deallocations by $STKMRET. */
308 long segments; /* Current number of stack segments. */
309 long maxs; /* Maximum number of stack segments so far. */
310 long pad_size; /* Stack pad size. */
311 long current_address; /* Current stack segment address. */
312 long current_size; /* Current stack segment size. This
313 number is actually corrupted by STKSTAT to
314 include the fifteen word trailer area. */
315 long initial_address; /* Address of initial segment. */
316 long initial_size; /* Size of initial segment. */
319 /* The following structure describes the data structure which trails
320 any stack segment. I think that the description in 'asdef' is
321 out of date. I only describe the parts that I am sure about. */
325 long this_address; /* Address of this block. */
326 long this_size; /* Size of this block (does not include
330 long link; /* Address of trailer block of previous
345 #endif /* not CRAY_STACK */
348 /* Determine a "stack measure" for an arbitrary ADDRESS.
349 I doubt that "lint" will like this much. */
352 i00afunc (long *address)
354 struct stk_stat status;
355 struct stk_trailer *trailer;
359 /* We want to iterate through all of the segments. The first
360 step is to get the stack status structure. We could do this
361 more quickly and more directly, perhaps, by referencing the
362 $LM00 common block, but I know that this works. */
366 /* Set up the iteration. */
368 trailer = (struct stk_trailer *) (status.current_address
369 + status.current_size
372 /* There must be at least one stack segment. Therefore it is
373 a fatal error if "trailer" is null. */
378 /* Discard segments that do not contain our argument address. */
382 block = (long *) trailer->this_address;
383 size = trailer->this_size;
384 if (block == 0 || size == 0)
386 trailer = (struct stk_trailer *) trailer->link;
387 if ((block <= address) && (address < (block + size)))
391 /* Set the result to the offset in this segment and add the sizes
392 of all predecessor segments. */
394 result = address - block;
403 if (trailer->this_size <= 0)
405 result += trailer->this_size;
406 trailer = (struct stk_trailer *) trailer->link;
408 while (trailer != 0);
410 /* We are done. Note that if you present a bogus address (one
411 not in any segment), you will get a different number back, formed
412 from subtracting the address of the first block. This is probably
413 not what you want. */
418 #else /* not CRAY2 */
419 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
420 Determine the number of the cell within the stack,
421 given the address of the cell. The purpose of this
422 routine is to linearize, in some sense, stack addresses
426 i00afunc (long address)
430 long size, pseg, this_segment, stack;
433 struct stack_segment_linkage *ssptr;
435 /* Register B67 contains the address of the end of the
436 current stack segment. If you (as a subprogram) store
437 your registers on the stack and find that you are past
438 the contents of B67, you have overflowed the segment.
440 B67 also points to the stack segment linkage control
441 area, which is what we are really interested in. */
443 stkl = CRAY_STACKSEG_END ();
444 ssptr = (struct stack_segment_linkage *) stkl;
446 /* If one subtracts 'size' from the end of the segment,
447 one has the address of the first word of the segment.
449 If this is not the first segment, 'pseg' will be
452 pseg = ssptr->sspseg;
453 size = ssptr->sssize;
455 this_segment = stkl - size;
457 /* It is possible that calling this routine itself caused
458 a stack overflow. Discard stack segments which do not
459 contain the target address. */
461 while (!(this_segment <= address && address <= stkl))
463 #ifdef DEBUG_I00AFUNC
464 fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
469 ssptr = (struct stack_segment_linkage *) stkl;
470 size = ssptr->sssize;
471 pseg = ssptr->sspseg;
472 this_segment = stkl - size;
475 result = address - this_segment;
477 /* If you subtract pseg from the current end of the stack,
478 you get the address of the previous stack segment's end.
479 This seems a little convoluted to me, but I'll bet you save
480 a cycle somewhere. */
484 #ifdef DEBUG_I00AFUNC
485 fprintf (stderr, "%011o %011o\n", pseg, size);
488 ssptr = (struct stack_segment_linkage *) stkl;
489 size = ssptr->sssize;
490 pseg = ssptr->sspseg;
496 #endif /* not CRAY2 */
499 #endif /* no alloca */