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
#endif /* STACK_DIRECTION undefined */
59
/* If your stack is a linked list of frames, you have to
60
provide an "address metric" ADDRESS_FUNCTION macro. */
62
#if defined (CRAY) && defined (CRAY_STACKSEG_END)
64
#define ADDRESS_FUNCTION(arg) (char *) i00afunc (&(arg))
66
#define ADDRESS_FUNCTION(arg) &(arg)
70
typedef void *pointer;
72
typedef char *pointer;
79
/* Different portions of Emacs need to call different versions of
80
malloc. The Emacs executable needs alloca to call xmalloc, because
81
ordinary malloc isn't protected from input signals. On the other
82
hand, the utilities in lib-src need alloca to call malloc; some of
83
them are very simple, and don't have an xmalloc routine.
85
Non-Emacs programs expect this to call xmalloc.
87
Callers below should use malloc. */
91
#define malloc xmalloc
94
extern pointer malloc ();
96
/* Define STACK_DIRECTION if you know the direction of stack
97
growth for your system; otherwise it will be automatically
100
STACK_DIRECTION > 0 => grows toward higher addresses
101
STACK_DIRECTION < 0 => grows toward lower addresses
102
STACK_DIRECTION = 0 => direction of growth unknown */
104
#ifndef STACK_DIRECTION
105
#define STACK_DIRECTION 0 /* Direction unknown. */
108
#if STACK_DIRECTION != 0
110
#define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
112
#else /* STACK_DIRECTION == 0; need run-time code. */
114
static int stack_dir; /* 1 or -1 once known. */
115
#define STACK_DIR stack_dir
118
find_stack_direction ()
120
static char *addr = NULL; /* Address of first `dummy', once known. */
121
auto char dummy; /* To get stack address. */
124
{ /* Initial entry. */
125
addr = ADDRESS_FUNCTION (dummy);
127
find_stack_direction (); /* Recurse once. */
132
if (ADDRESS_FUNCTION (dummy) > addr)
133
stack_dir = 1; /* Stack grew upward. */
135
stack_dir = -1; /* Stack grew downward. */
139
#endif /* STACK_DIRECTION == 0 */
141
/* An "alloca header" is used to:
142
(a) chain together all alloca'ed blocks;
143
(b) keep track of stack depth.
145
It is very important that sizeof(header) agree with malloc
146
alignment chunk size. The following default should work okay. */
149
#define ALIGN_SIZE sizeof(double)
154
char align[ALIGN_SIZE]; /* To force sizeof(header). */
157
union hdr *next; /* For chaining headers. */
158
char *deep; /* For stack depth measure. */
162
static header *last_alloca_header = NULL; /* -> last alloca header. */
164
/* Return a pointer to at least SIZE bytes of storage,
165
which will be automatically reclaimed upon exit from
166
the procedure that called alloca. Originally, this space
167
was supposed to be taken from the current stack frame of the
168
caller, but that method cannot be made to work for some
169
implementations of C, for example under Gould's UTX/32. */
175
auto char probe; /* Probes stack depth: */
176
register char *depth = ADDRESS_FUNCTION (probe);
178
#if STACK_DIRECTION == 0
179
if (STACK_DIR == 0) /* Unknown growth direction. */
180
find_stack_direction ();
183
/* Reclaim garbage, defined as all alloca'd storage that
184
was allocated from deeper in the stack than currently. */
187
register header *hp; /* Traverses linked list. */
193
for (hp = last_alloca_header; hp != NULL;)
194
if ((STACK_DIR > 0 && hp->h.deep > depth)
195
|| (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. */
204
break; /* Rest are not deeper. */
206
last_alloca_header = hp; /* -> last valid storage. */
214
return NULL; /* No allocation required. */
216
/* Allocate combined header + user data storage. */
219
register pointer new = malloc (sizeof (header) + size);
220
/* Address of header. */
225
((header *) new)->h.next = last_alloca_header;
226
((header *) new)->h.deep = depth;
228
last_alloca_header = (header *) new;
230
/* User storage begins just after header. */
232
return (pointer) ((char *) new + sizeof (header));
236
#if defined (CRAY) && defined (CRAY_STACKSEG_END)
238
#ifdef DEBUG_I00AFUNC
245
/* Stack structures for CRAY-1, CRAY X-MP, and CRAY Y-MP */
246
struct stack_control_header
248
long shgrow:32; /* Number of times stack has grown. */
249
long shaseg:32; /* Size of increments to stack. */
250
long shhwm:32; /* High water mark of stack. */
251
long shsize:32; /* Current size of stack (all segments). */
254
/* The stack segment linkage control information occurs at
255
the high-address end of a stack segment. (The stack
256
grows from low addresses to high addresses.) The initial
257
part of the stack segment linkage control information is
258
0200 (octal) words. This provides for register storage
259
for the routine which overflows the stack. */
261
struct stack_segment_linkage
263
long ss[0200]; /* 0200 overflow words. */
264
long sssize:32; /* Number of words in this segment. */
265
long ssbase:32; /* Offset to stack base. */
267
long sspseg:32; /* Offset to linkage control of previous
270
long sstcpt:32; /* Pointer to task common address block. */
271
long sscsnm; /* Private control structure number for
273
long ssusr1; /* Reserved for user. */
274
long ssusr2; /* Reserved for user. */
275
long sstpid; /* Process ID for pid based multi-tasking. */
276
long ssgvup; /* Pointer to multitasking thread giveup. */
277
long sscray[7]; /* Reserved for Cray Research. */
297
/* The following structure defines the vector of words
298
returned by the STKSTAT library routine. */
301
long now; /* Current total stack size. */
302
long maxc; /* Amount of contiguous space which would
303
be required to satisfy the maximum
304
stack demand to date. */
305
long high_water; /* Stack high-water mark. */
306
long overflows; /* Number of stack overflow ($STKOFEN) calls. */
307
long hits; /* Number of internal buffer hits. */
308
long extends; /* Number of block extensions. */
309
long stko_mallocs; /* Block allocations by $STKOFEN. */
310
long underflows; /* Number of stack underflow calls ($STKRETN). */
311
long stko_free; /* Number of deallocations by $STKRETN. */
312
long stkm_free; /* Number of deallocations by $STKMRET. */
313
long segments; /* Current number of stack segments. */
314
long maxs; /* Maximum number of stack segments so far. */
315
long pad_size; /* Stack pad size. */
316
long current_address; /* Current stack segment address. */
317
long current_size; /* Current stack segment size. This
318
number is actually corrupted by STKSTAT to
319
include the fifteen word trailer area. */
320
long initial_address; /* Address of initial segment. */
321
long initial_size; /* Size of initial segment. */
324
/* The following structure describes the data structure which trails
325
any stack segment. I think that the description in 'asdef' is
326
out of date. I only describe the parts that I am sure about. */
330
long this_address; /* Address of this block. */
331
long this_size; /* Size of this block (does not include
335
long link; /* Address of trailer block of previous
350
#endif /* not CRAY_STACK */
353
/* Determine a "stack measure" for an arbitrary ADDRESS.
354
I doubt that "lint" will like this much. */
357
i00afunc (long *address)
359
struct stk_stat status;
360
struct stk_trailer *trailer;
364
/* We want to iterate through all of the segments. The first
365
step is to get the stack status structure. We could do this
366
more quickly and more directly, perhaps, by referencing the
367
$LM00 common block, but I know that this works. */
371
/* Set up the iteration. */
373
trailer = (struct stk_trailer *) (status.current_address
374
+ status.current_size
377
/* There must be at least one stack segment. Therefore it is
378
a fatal error if "trailer" is null. */
383
/* Discard segments that do not contain our argument address. */
387
block = (long *) trailer->this_address;
388
size = trailer->this_size;
389
if (block == 0 || size == 0)
391
trailer = (struct stk_trailer *) trailer->link;
392
if ((block <= address) && (address < (block + size)))
396
/* Set the result to the offset in this segment and add the sizes
397
of all predecessor segments. */
399
result = address - block;
408
if (trailer->this_size <= 0)
410
result += trailer->this_size;
411
trailer = (struct stk_trailer *) trailer->link;
413
while (trailer != 0);
415
/* We are done. Note that if you present a bogus address (one
416
not in any segment), you will get a different number back, formed
417
from subtracting the address of the first block. This is probably
418
not what you want. */
423
#else /* not CRAY2 */
424
/* Stack address function for a CRAY-1, CRAY X-MP, or CRAY Y-MP.
425
Determine the number of the cell within the stack,
426
given the address of the cell. The purpose of this
427
routine is to linearize, in some sense, stack addresses
431
i00afunc (long address)
435
long size, pseg, this_segment, stack;
438
struct stack_segment_linkage *ssptr;
440
/* Register B67 contains the address of the end of the
441
current stack segment. If you (as a subprogram) store
442
your registers on the stack and find that you are past
443
the contents of B67, you have overflowed the segment.
445
B67 also points to the stack segment linkage control
446
area, which is what we are really interested in. */
448
stkl = CRAY_STACKSEG_END ();
449
ssptr = (struct stack_segment_linkage *) stkl;
451
/* If one subtracts 'size' from the end of the segment,
452
one has the address of the first word of the segment.
454
If this is not the first segment, 'pseg' will be
457
pseg = ssptr->sspseg;
458
size = ssptr->sssize;
460
this_segment = stkl - size;
462
/* It is possible that calling this routine itself caused
463
a stack overflow. Discard stack segments which do not
464
contain the target address. */
466
while (!(this_segment <= address && address <= stkl))
468
#ifdef DEBUG_I00AFUNC
469
fprintf (stderr, "%011o %011o %011o\n", this_segment, address, stkl);
474
ssptr = (struct stack_segment_linkage *) stkl;
475
size = ssptr->sssize;
476
pseg = ssptr->sspseg;
477
this_segment = stkl - size;
480
result = address - this_segment;
482
/* If you subtract pseg from the current end of the stack,
483
you get the address of the previous stack segment's end.
484
This seems a little convoluted to me, but I'll bet you save
485
a cycle somewhere. */
489
#ifdef DEBUG_I00AFUNC
490
fprintf (stderr, "%011o %011o\n", pseg, size);
493
ssptr = (struct stack_segment_linkage *) stkl;
494
size = ssptr->sssize;
495
pseg = ssptr->sspseg;
501
#endif /* not CRAY2 */
504
#endif /* no alloca */
505
#endif /* not GCC version 2 */
added
removed
src/alloca.c
