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
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
|
/* Common definitions.
Copyright (C) 1986-2023 Free Software Foundation, Inc.
This file is part of GDB.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see <http://www.gnu.org/licenses/>. */
#ifndef COMMON_COMMON_DEFS_H
#define COMMON_COMMON_DEFS_H
#include <gdbsupport/config.h>
#undef PACKAGE_NAME
#undef PACKAGE
#undef PACKAGE_VERSION
#undef PACKAGE_STRING
#undef PACKAGE_TARNAME
#include "gnulib/config.h"
/* From:
https://www.gnu.org/software/gnulib/manual/html_node/stdint_002eh.html
"On some hosts that predate C++11, when using C++ one must define
__STDC_CONSTANT_MACROS to make visible the definitions of constant
macros such as INTMAX_C, and one must define __STDC_LIMIT_MACROS to
make visible the definitions of limit macros such as INTMAX_MAX.".
And:
https://www.gnu.org/software/gnulib/manual/html_node/inttypes_002eh.html
"On some hosts that predate C++11, when using C++ one must define
__STDC_FORMAT_MACROS to make visible the declarations of format
macros such as PRIdMAX."
Must do this before including any system header, since other system
headers may include stdint.h/inttypes.h. */
#define __STDC_CONSTANT_MACROS 1
#define __STDC_LIMIT_MACROS 1
#define __STDC_FORMAT_MACROS 1
/* Some distros enable _FORTIFY_SOURCE by default, which on occasion
has caused build failures with -Wunused-result when a patch is
developed on a distro that does not enable _FORTIFY_SOURCE. We
enable it here in order to try to catch these problems earlier;
plus this seems like a reasonable safety measure. The check for
optimization is required because _FORTIFY_SOURCE only works when
optimization is enabled. If _FORTIFY_SOURCE is already defined,
then we don't do anything. Also, on MinGW, fortify requires
linking to -lssp, and to avoid the hassle of checking for
that and linking to it statically, we just don't define
_FORTIFY_SOURCE there. */
#if (!defined _FORTIFY_SOURCE && defined __OPTIMIZE__ && __OPTIMIZE__ > 0 \
&& !defined(__MINGW32__))
#define _FORTIFY_SOURCE 2
#endif
/* We don't support Windows versions before XP, so we define
_WIN32_WINNT correspondingly to ensure the Windows API headers
expose the required symbols.
NOTE: this must be kept in sync with common.m4. */
#if defined (__MINGW32__) || defined (__CYGWIN__)
# ifdef _WIN32_WINNT
# if _WIN32_WINNT < 0x0501
# undef _WIN32_WINNT
# define _WIN32_WINNT 0x0501
# endif
# else
# define _WIN32_WINNT 0x0501
# endif
#endif /* __MINGW32__ || __CYGWIN__ */
#include <stdarg.h>
#include <stdio.h>
/* Include both cstdlib and stdlib.h to ensure we have standard functions
defined both in the std:: namespace and in the global namespace. */
#include <cstdlib>
#include <stdlib.h>
#include <stddef.h>
#include <stdint.h>
#include <string.h>
#ifdef HAVE_STRINGS_H
#include <strings.h> /* for strcasecmp and strncasecmp */
#endif
#include <errno.h>
#if HAVE_ALLOCA_H
#include <alloca.h>
#endif
#include "ansidecl.h"
/* This is defined by ansidecl.h, but we prefer gnulib's version. On
MinGW, gnulib might enable __USE_MINGW_ANSI_STDIO, which may or not
require use of attribute gnu_printf instead of printf. gnulib
checks that at configure time. Since _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD
is compatible with ATTRIBUTE_PRINTF, simply use it. */
#undef ATTRIBUTE_PRINTF
#define ATTRIBUTE_PRINTF _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD
/* This is defined by ansidecl.h, but we disable the attribute.
Say a developer starts out with:
...
extern void foo (void *ptr) __attribute__((nonnull (1)));
void foo (void *ptr) {}
...
with the idea in mind to catch:
...
foo (nullptr);
...
at compile time with -Werror=nonnull, and then adds:
...
void foo (void *ptr) {
+ gdb_assert (ptr != nullptr);
}
...
to catch:
...
foo (variable_with_nullptr_value);
...
at runtime as well.
Said developer then verifies that the assert works (using -O0), and commits
the code.
Some other developer then checks out the code and accidentally writes some
variant of:
...
foo (variable_with_nullptr_value);
...
and builds with -O2, and ... the assert doesn't trigger, because it's
optimized away by gcc.
There's no suppported recipe to prevent the assertion from being optimized
away (other than: build with -O0, or remove the nonnull attribute). Note
that -fno-delete-null-pointer-checks does not help. A patch was submitted
to improve gcc documentation to point this out more clearly (
https://gcc.gnu.org/pipermail/gcc-patches/2021-July/576218.html ). The
patch also mentions a possible workaround that obfuscates the pointer
using:
...
void foo (void *ptr) {
+ asm ("" : "+r"(ptr));
gdb_assert (ptr != nullptr);
}
...
but that still requires the developer to manually add this in all cases
where that's necessary.
A warning was added to detect the situation: -Wnonnull-compare, which does
help in detecting those cases, but each new gcc release may indicate a new
batch of locations that needs fixing, which means we've added a maintenance
burden.
We could try to deal with the problem more proactively by introducing a
gdb_assert variant like:
...
void gdb_assert_non_null (void *ptr) {
asm ("" : "+r"(ptr));
gdb_assert (ptr != nullptr);
}
void foo (void *ptr) {
gdb_assert_nonnull (ptr);
}
...
and make it a coding style to use it everywhere, but again, maintenance
burden.
With all these things considered, for now we go with the solution with the
least maintenance burden: disable the attribute, such that we reliably deal
with it everywhere. */
#undef ATTRIBUTE_NONNULL
#define ATTRIBUTE_NONNULL(m)
#if GCC_VERSION >= 3004
#define ATTRIBUTE_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
#else
#define ATTRIBUTE_UNUSED_RESULT
#endif
#if (GCC_VERSION > 4000)
#define ATTRIBUTE_USED __attribute__ ((__used__))
#else
#define ATTRIBUTE_USED
#endif
#include "libiberty.h"
#include "pathmax.h"
#include "gdb/signals.h"
#include "gdb_locale.h"
#include "ptid.h"
#include "common-types.h"
#include "common-utils.h"
#include "gdb_assert.h"
#include "errors.h"
#include "print-utils.h"
#include "common-debug.h"
#include "cleanups.h"
#include "common-exceptions.h"
#include "gdbsupport/poison.h"
#define EXTERN_C extern "C"
#define EXTERN_C_PUSH extern "C" {
#define EXTERN_C_POP }
/* Pull in gdb::unique_xmalloc_ptr. */
#include "gdbsupport/gdb_unique_ptr.h"
/* sbrk on macOS is not useful for our purposes, since sbrk(0) always
returns the same value. brk/sbrk on macOS is just an emulation
that always returns a pointer to a 4MB section reserved for
that. */
#if defined (HAVE_SBRK) && !__APPLE__
#define HAVE_USEFUL_SBRK 1
#endif
#endif /* COMMON_COMMON_DEFS_H */
|
