1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
|
/* alloca.c -- allocate automatically reclaimed memory
(Mostly) portable public-domain implementation -- D A Gwyn
This implementation of the PWB library alloca function,
which is used to allocate space off the run-time stack so
that it is automatically reclaimed upon procedure exit,
was inspired by discussions with J. Q. Johnson of Cornell.
J.Otto Tennant <jot@cray.com> contributed the Cray support.
There are some preprocessor constants that can
be defined when compiling for your specific system, for
improved efficiency; however, the defaults should be okay.
The general concept of this implementation is to keep
track of all alloca-allocated blocks, and reclaim any
that are found to be deeper in the stack than the current
invocation. This heuristic does not reclaim storage as
soon as it becomes invalid, but it will do so eventually.
As a special case, alloca(0) reclaims storage without
allocating any. It is a good idea to use alloca(0) in
your main control loop, etc. to force garbage collection. */
#include <config.h>
#include <alloca.h>
#include <string.h>
#include <stdlib.h>
#ifdef emacs
# include "lisp.h"
# include "blockinput.h"
# ifdef EMACS_FREE
# undef free
# define free EMACS_FREE
# endif
#else
# define memory_full() abort ()
#endif
/* If compiling with GCC or clang, this file is not needed. */
#if !(defined __GNUC__ || defined __clang__)
/* If someone has defined alloca as a macro,
there must be some other way alloca is supposed to work. */
# ifndef alloca
# ifdef emacs
# ifdef static
/* actually, only want this if static is defined as ""
-- this is for usg, in which emacs must undefine static
in order to make unexec workable
*/
# ifndef STACK_DIRECTION
you
lose
-- must know STACK_DIRECTION at compile-time
/* Using #error here is not wise since this file should work for
old and obscure compilers. */
# endif /* STACK_DIRECTION undefined */
# endif /* static */
# endif /* emacs */
/* Define STACK_DIRECTION if you know the direction of stack
growth for your system; otherwise it will be automatically
deduced at run-time.
STACK_DIRECTION > 0 => grows toward higher addresses
STACK_DIRECTION < 0 => grows toward lower addresses
STACK_DIRECTION = 0 => direction of growth unknown */
# ifndef STACK_DIRECTION
# define STACK_DIRECTION 0 /* Direction unknown. */
# endif
# if STACK_DIRECTION != 0
# define STACK_DIR STACK_DIRECTION /* Known at compile-time. */
# else /* STACK_DIRECTION == 0; need run-time code. */
static int stack_dir; /* 1 or -1 once known. */
# define STACK_DIR stack_dir
static int
find_stack_direction (int *addr, int depth)
{
int dir, dummy = 0;
if (! addr)
addr = &dummy;
*addr = addr < &dummy ? 1 : addr == &dummy ? 0 : -1;
dir = depth ? find_stack_direction (addr, depth - 1) : 0;
return dir + dummy;
}
# endif /* STACK_DIRECTION == 0 */
/* An "alloca header" is used to:
(a) chain together all alloca'ed blocks;
(b) keep track of stack depth.
It is very important that sizeof(header) agree with malloc
alignment chunk size. The following default should work okay. */
# ifndef ALIGN_SIZE
# define ALIGN_SIZE sizeof(double)
# endif
typedef union hdr
{
char align[ALIGN_SIZE]; /* To force sizeof(header). */
struct
{
union hdr *next; /* For chaining headers. */
char *deep; /* For stack depth measure. */
} h;
} header;
static header *last_alloca_header = NULL; /* -> last alloca header. */
/* Return a pointer to at least SIZE bytes of storage,
which will be automatically reclaimed upon exit from
the procedure that called alloca. Originally, this space
was supposed to be taken from the current stack frame of the
caller, but that method cannot be made to work for some
implementations of C, for example under Gould's UTX/32. */
void *
alloca (size_t size)
{
auto char probe; /* Probes stack depth: */
register char *depth = &probe;
# if STACK_DIRECTION == 0
if (STACK_DIR == 0) /* Unknown growth direction. */
STACK_DIR = find_stack_direction (NULL, (size & 1) + 20);
# endif
/* Reclaim garbage, defined as all alloca'd storage that
was allocated from deeper in the stack than currently. */
{
register header *hp; /* Traverses linked list. */
# ifdef emacs
BLOCK_INPUT;
# endif
for (hp = last_alloca_header; hp != NULL;)
if ((STACK_DIR > 0 && hp->h.deep > depth)
|| (STACK_DIR < 0 && hp->h.deep < depth))
{
register header *np = hp->h.next;
free (hp); /* Collect garbage. */
hp = np; /* -> next header. */
}
else
break; /* Rest are not deeper. */
last_alloca_header = hp; /* -> last valid storage. */
# ifdef emacs
UNBLOCK_INPUT;
# endif
}
if (size == 0)
return NULL; /* No allocation required. */
/* Allocate combined header + user data storage. */
{
/* Address of header. */
register header *new;
size_t combined_size = sizeof (header) + size;
if (combined_size < sizeof (header))
memory_full ();
new = malloc (combined_size);
if (! new)
memory_full ();
new->h.next = last_alloca_header;
new->h.deep = depth;
last_alloca_header = new;
/* User storage begins just after header. */
return (void *) (new + 1);
}
}
# endif /* no alloca */
#endif /* not GCC || clang */
|
