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. */
37 #include "blockinput.h"
40 /* If compiling with GCC 2, this file's not needed. */
41 #if !defined (__GNUC__) || __GNUC__ < 2
43 /* If someone has defined alloca as a macro,
44 there must be some other way alloca is supposed to work. */
49 /* actually, only want this if static is defined as ""
50 -- this is for usg, in which emacs must undefine static
51 in order to make unexec workable
53 #ifndef STACK_DIRECTION
56 -- must know STACK_DIRECTION at compile
-time
57 #endif /* STACK_DIRECTION undefined */
61 /* If your stack is a linked list of frames, you have to
62 provide an "address metric" ADDRESS_FUNCTION macro. */
64 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
66 #define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
68 #define ADDRESS_FUNCTION(arg) &(arg)
72 typedef void *pointer
;
74 typedef char *pointer
;
81 /* Different portions of Emacs need to call different versions of
82 malloc. The Emacs executable needs alloca to call xmalloc, because
83 ordinary malloc isn't protected from input signals. On the other
84 hand, the utilities in lib-src need alloca to call malloc; some of
85 them are very simple, and don't have an xmalloc routine.
87 Non-Emacs programs expect this to call use xmalloc.
89 Callers below should use malloc. */
92 #define malloc xmalloc
94 #define free EMACS_FREE
97 extern pointer
malloc ();
99 /* Define STACK_DIRECTION if you know the direction of stack
100 growth for your system; otherwise it will be automatically
103 STACK_DIRECTION > 0 => grows toward higher addresses
104 STACK_DIRECTION < 0 => grows toward lower addresses
105 STACK_DIRECTION = 0 => direction of growth unknown */
107 #ifndef STACK_DIRECTION
108 #define STACK_DIRECTION 0 /* Direction unknown. */
111 #if STACK_DIRECTION != 0
113 #define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
115 #else /* STACK_DIRECTION == 0; need run-time code. */
117 static int stack_dir
; /* 1 or -1 once known. */
118 #define STACK_DIR stack_dir
121 find_stack_direction ()
123 static char *addr
= NULL
; /* Address of first `dummy', once known. */
124 auto char dummy
; /* To get stack address. */
127 { /* Initial entry. */
128 addr
= ADDRESS_FUNCTION (dummy
);
130 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)
157 char align
[ALIGN_SIZE
]; /* To force sizeof(header). */
160 union hdr
*next
; /* For chaining headers. */
161 char *deep
; /* For stack depth measure. */
165 static header
*last_alloca_header
= NULL
; /* -> last alloca header. */
167 /* Return a pointer to at least SIZE bytes of storage,
168 which will be automatically reclaimed upon exit from
169 the procedure that called alloca. Originally, this space
170 was supposed to be taken from the current stack frame of the
171 caller, but that method cannot be made to work for some
172 implementations of C, for example under Gould's UTX/32. */
178 auto char probe
; /* Probes stack depth: */
179 register char *depth
= ADDRESS_FUNCTION (probe
);
181 #if STACK_DIRECTION == 0
182 if (STACK_DIR
== 0) /* Unknown growth direction. */
183 find_stack_direction ();
186 /* Reclaim garbage, defined as all alloca'd storage that
187 was allocated from deeper in the stack than currently. */
190 register header
*hp
; /* Traverses linked list. */
196 for (hp
= last_alloca_header
; hp
!= NULL
;)
197 if ((STACK_DIR
> 0 && hp
->h
.deep
> depth
)
198 || (STACK_DIR
< 0 && hp
->h
.deep
< depth
))
200 register header
*np
= hp
->h
.next
;
202 free ((pointer
) hp
); /* Collect garbage. */
204 hp
= np
; /* -> next header. */
207 break; /* Rest are not deeper. */
209 last_alloca_header
= hp
; /* -> last valid storage. */
217 return NULL
; /* No allocation required. */
219 /* Allocate combined header + user data storage. */
222 register pointer
new = malloc (sizeof (header
) + size
);
223 /* Address of header. */
228 ((header
*) new)->h
.next
= last_alloca_header
;
229 ((header
*) new)->h
.deep
= depth
;
231 last_alloca_header
= (header
*) new;
233 /* User storage begins just after header. */
235 return (pointer
) ((char *) new + sizeof (header
));
239 #if defined (CRAY) && defined (CRAY_STACKSEG_END)
241 #ifdef DEBUG_I00AFUNC
248 /* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
249 struct stack_control_header
251 long shgrow
:32; /* Number of times stack has grown. */
252 long shaseg
:32; /* Size of increments to stack. */
253 long shhwm
:32; /* High water mark of stack. */
254 long shsize
:32; /* Current size of stack (all segments). */
257 /* The stack segment linkage control information occurs at
258 the high-address end of a stack segment. (The stack
259 grows from low addresses to high addresses.) The initial
260 part of the stack segment linkage control information is
261 0200 (octal) words. This provides for register storage
262 for the routine which overflows the stack. */
264 struct stack_segment_linkage
266 long ss
[0200]; /* 0200 overflow words. */
267 long sssize
:32; /* Number of words in this segment. */
268 long ssbase
:32; /* Offset to stack base. */
270 long sspseg
:32; /* Offset to linkage control of previous
273 long sstcpt
:32; /* Pointer to task common address block. */
274 long sscsnm
; /* Private control structure number for
276 long ssusr1
; /* Reserved for user. */
277 long ssusr2
; /* Reserved for user. */
278 long sstpid
; /* Process ID for pid based multi-tasking. */
279 long ssgvup
; /* Pointer to multitasking thread giveup. */
280 long sscray
[7]; /* Reserved for Cray Research. */
300 /* The following structure defines the vector of words
301 returned by the STKSTAT library routine. */
304 long now
; /* Current total stack size. */
305 long maxc
; /* Amount of contiguous space which would
306 be required to satisfy the maximum
307 stack demand to date. */
308 long high_water
; /* Stack high-water mark. */
309 long overflows
; /* Number of stack overflow ($STKOFEN) calls. */
310 long hits
; /* Number of internal buffer hits. */
311 long extends
; /* Number of block extensions. */
312 long stko_mallocs
; /* Block allocations by $STKOFEN. */
313 long underflows
; /* Number of stack underflow calls ($STKRETN). */
314 long stko_free
; /* Number of deallocations by $STKRETN. */
315 long stkm_free
; /* Number of deallocations by $STKMRET. */
316 long segments
; /* Current number of stack segments. */
317 long maxs
; /* Maximum number of stack segments so far. */
318 long pad_size
; /* Stack pad size. */
319 long current_address
; /* Current stack segment address. */
320 long current_size
; /* Current stack segment size. This
321 number is actually corrupted by STKSTAT to
322 include the fifteen word trailer area. */
323 long initial_address
; /* Address of initial segment. */
324 long initial_size
; /* Size of initial segment. */
327 /* The following structure describes the data structure which trails
328 any stack segment. I think that the description in 'asdef' is
329 out of date. I only describe the parts that I am sure about. */
333 long this_address
; /* Address of this block. */
334 long this_size
; /* Size of this block (does not include
338 long link
; /* Address of trailer block of previous
353 #endif /* not CRAY_STACK */
356 /* Determine a "stack measure" for an arbitrary ADDRESS.
357 I doubt that "lint" will like this much. */
360 i00afunc (long *address
)
362 struct stk_stat status
;
363 struct stk_trailer
*trailer
;
367 /* We want to iterate through all of the segments. The first
368 step is to get the stack status structure. We could do this
369 more quickly and more directly, perhaps, by referencing the
370 $LM00 common block, but I know that this works. */
374 /* Set up the iteration. */
376 trailer
= (struct stk_trailer
*) (status
.current_address
377 + status
.current_size
380 /* There must be at least one stack segment. Therefore it is
381 a fatal error if "trailer" is null. */
386 /* Discard segments that do not contain our argument address. */
390 block
= (long *) trailer
->this_address
;
391 size
= trailer
->this_size
;
392 if (block
== 0 || size
== 0)
394 trailer
= (struct stk_trailer
*) trailer
->link
;
395 if ((block
<= address
) && (address
< (block
+ size
)))
399 /* Set the result to the offset in this segment and add the sizes
400 of all predecessor segments. */
402 result
= address
- block
;
411 if (trailer
->this_size
<= 0)
413 result
+= trailer
->this_size
;
414 trailer
= (struct stk_trailer
*) trailer
->link
;
416 while (trailer
!= 0);
418 /* We are done. Note that if you present a bogus address (one
419 not in any segment), you will get a different number back, formed
420 from subtracting the address of the first block. This is probably
421 not what you want. */
426 #else /* not CRAY2 */
427 /* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
428 Determine the number of the cell within the stack,
429 given the address of the cell. The purpose of this
430 routine is to linearize, in some sense, stack addresses
434 i00afunc (long address
)
438 long size
, pseg
, this_segment
, stack
;
441 struct stack_segment_linkage
*ssptr
;
443 /* Register B67 contains the address of the end of the
444 current stack segment. If you (as a subprogram) store
445 your registers on the stack and find that you are past
446 the contents of B67, you have overflowed the segment.
448 B67 also points to the stack segment linkage control
449 area, which is what we are really interested in. */
451 stkl
= CRAY_STACKSEG_END ();
452 ssptr
= (struct stack_segment_linkage
*) stkl
;
454 /* If one subtracts 'size' from the end of the segment,
455 one has the address of the first word of the segment.
457 If this is not the first segment, 'pseg' will be
460 pseg
= ssptr
->sspseg
;
461 size
= ssptr
->sssize
;
463 this_segment
= stkl
- size
;
465 /* It is possible that calling this routine itself caused
466 a stack overflow. Discard stack segments which do not
467 contain the target address. */
469 while (!(this_segment
<= address
&& address
<= stkl
))
471 #ifdef DEBUG_I00AFUNC
472 fprintf (stderr
, "%011o %011o %011o\n", this_segment
, address
, stkl
);
477 ssptr
= (struct stack_segment_linkage
*) stkl
;
478 size
= ssptr
->sssize
;
479 pseg
= ssptr
->sspseg
;
480 this_segment
= stkl
- size
;
483 result
= address
- this_segment
;
485 /* If you subtract pseg from the current end of the stack,
486 you get the address of the previous stack segment's end.
487 This seems a little convoluted to me, but I'll bet you save
488 a cycle somewhere. */
492 #ifdef DEBUG_I00AFUNC
493 fprintf (stderr
, "%011o %011o\n", pseg
, size
);
496 ssptr
= (struct stack_segment_linkage
*) stkl
;
497 size
= ssptr
->sssize
;
498 pseg
= ssptr
->sspseg
;
504 #endif /* not CRAY2 */
507 #endif /* no alloca */
508 #endif /* not GCC version 2 */