gdbsupport/common-defs.h

   1 /* Common definitions.
   2
   3    Copyright (C) 1986-2024 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20 #ifndef COMMON_COMMON_DEFS_H
  21 #define COMMON_COMMON_DEFS_H
  22
  23 #if defined (__SANITIZE_THREAD__) && defined (__GNUC__) \
  24   && !defined (__clang__) && __GNUC__ <= 13
  25
  26 /* Work around PR gcc/110799.  */
  27 #pragma GCC optimize("-fno-hoist-adjacent-loads")
  28 #endif
  29
  30 #include <gdbsupport/config.h>
  31
  32 #undef PACKAGE_NAME
  33 #undef PACKAGE
  34 #undef PACKAGE_VERSION
  35 #undef PACKAGE_STRING
  36 #undef PACKAGE_TARNAME
  37
  38 #include "gnulib/config.h"
  39
  40 /* From:
  41     https://www.gnu.org/software/gnulib/manual/html_node/stdint_002eh.html
  42
  43    "On some hosts that predate C++11, when using C++ one must define
  44    __STDC_CONSTANT_MACROS to make visible the definitions of constant
  45    macros such as INTMAX_C, and one must define __STDC_LIMIT_MACROS to
  46    make visible the definitions of limit macros such as INTMAX_MAX.".
  47
  48    And:
  49     https://www.gnu.org/software/gnulib/manual/html_node/inttypes_002eh.html
  50
  51    "On some hosts that predate C++11, when using C++ one must define
  52    __STDC_FORMAT_MACROS to make visible the declarations of format
  53    macros such as PRIdMAX."
  54
  55    Must do this before including any system header, since other system
  56    headers may include stdint.h/inttypes.h.  */
  57 #define __STDC_CONSTANT_MACROS 1
  58 #define __STDC_LIMIT_MACROS 1
  59 #define __STDC_FORMAT_MACROS 1
  60
  61 /* Some distros enable _FORTIFY_SOURCE by default, which on occasion
  62    has caused build failures with -Wunused-result when a patch is
  63    developed on a distro that does not enable _FORTIFY_SOURCE.  We
  64    enable it here in order to try to catch these problems earlier;
  65    plus this seems like a reasonable safety measure.  The check for
  66    optimization is required because _FORTIFY_SOURCE only works when
  67    optimization is enabled.  If _FORTIFY_SOURCE is already defined,
  68    then we don't do anything.  Also, on MinGW, fortify requires
  69    linking to -lssp, and to avoid the hassle of checking for
  70    that and linking to it statically, we just don't define
  71    _FORTIFY_SOURCE there.  */
  72
  73 #if (!defined _FORTIFY_SOURCE && defined __OPTIMIZE__ && __OPTIMIZE__ > 0 \
  74      && !defined(__MINGW32__))
  75 #define _FORTIFY_SOURCE 2
  76 #endif
  77
  78 /* We don't support Windows versions before XP, so we define
  79    _WIN32_WINNT correspondingly to ensure the Windows API headers
  80    expose the required symbols.
  81
  82    NOTE: this must be kept in sync with common.m4.  */
  83 #if defined (__MINGW32__) || defined (__CYGWIN__)
  84 # ifdef _WIN32_WINNT
  85 #  if _WIN32_WINNT < 0x0501
  86 #   undef _WIN32_WINNT
  87 #   define _WIN32_WINNT 0x0501
  88 #  endif
  89 # else
  90 #  define _WIN32_WINNT 0x0501
  91 # endif
  92 #endif  /* __MINGW32__ || __CYGWIN__ */
  93
  94 #include <stdarg.h>
  95 #include <stdio.h>
  96
  97 /* Include both cstdlib and stdlib.h to ensure we have standard functions
  98    defined both in the std:: namespace and in the global namespace.  */
  99 #include <cstdlib>
 100 #include <stdlib.h>
 101
 102 #include <stddef.h>
 103 #include <stdint.h>
 104 #include <string.h>
 105 #ifdef HAVE_STRINGS_H
 106 #include <strings.h>
 107 #endif
 108 #include <errno.h>
 109 #if HAVE_ALLOCA_H
 110 #include <alloca.h>
 111 #endif
 112
 113 #include "ansidecl.h"
 114 /* This is defined by ansidecl.h, but we prefer gnulib's version.  On
 115    MinGW, gnulib might enable __USE_MINGW_ANSI_STDIO, which may or not
 116    require use of attribute gnu_printf instead of printf.  gnulib
 117    checks that at configure time.  Since _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD
 118    is compatible with ATTRIBUTE_PRINTF, simply use it.  */
 119 #undef ATTRIBUTE_PRINTF
 120 #define ATTRIBUTE_PRINTF _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD
 121
 122 /* This is defined by ansidecl.h, but we disable the attribute.
 123
 124    Say a developer starts out with:
 125    ...
 126    extern void foo (void *ptr) __attribute__((nonnull (1)));
 127    void foo (void *ptr) {}
 128    ...
 129    with the idea in mind to catch:
 130    ...
 131    foo (nullptr);
 132    ...
 133    at compile time with -Werror=nonnull, and then adds:
 134    ...
 135     void foo (void *ptr) {
 136    +  gdb_assert (ptr != nullptr);
 137     }
 138    ...
 139    to catch:
 140    ...
 141    foo (variable_with_nullptr_value);
 142    ...
 143    at runtime as well.
 144
 145    Said developer then verifies that the assert works (using -O0), and commits
 146    the code.
 147
 148    Some other developer then checks out the code and accidentally writes some
 149    variant of:
 150    ...
 151    foo (variable_with_nullptr_value);
 152    ...
 153    and builds with -O2, and ... the assert doesn't trigger, because it's
 154    optimized away by gcc.
 155
 156    There's no suppported recipe to prevent the assertion from being optimized
 157    away (other than: build with -O0, or remove the nonnull attribute).  Note
 158    that -fno-delete-null-pointer-checks does not help.  A patch was submitted
 159    to improve gcc documentation to point this out more clearly (
 160    https://gcc.gnu.org/pipermail/gcc-patches/2021-July/576218.html ).  The
 161    patch also mentions a possible workaround that obfuscates the pointer
 162    using:
 163    ...
 164     void foo (void *ptr) {
 165    +  asm ("" : "+r"(ptr));
 166       gdb_assert (ptr != nullptr);
 167     }
 168    ...
 169    but that still requires the developer to manually add this in all cases
 170    where that's necessary.
 171
 172    A warning was added to detect the situation: -Wnonnull-compare, which does
 173    help in detecting those cases, but each new gcc release may indicate a new
 174    batch of locations that needs fixing, which means we've added a maintenance
 175    burden.
 176
 177    We could try to deal with the problem more proactively by introducing a
 178    gdb_assert variant like:
 179    ...
 180    void gdb_assert_non_null (void *ptr) {
 181       asm ("" : "+r"(ptr));
 182       gdb_assert (ptr != nullptr);
 183     }
 184     void foo (void *ptr) {
 185       gdb_assert_nonnull (ptr);
 186     }
 187    ...
 188    and make it a coding style to use it everywhere, but again, maintenance
 189    burden.
 190
 191    With all these things considered, for now we go with the solution with the
 192    least maintenance burden: disable the attribute, such that we reliably deal
 193    with it everywhere.  */
 194 #undef ATTRIBUTE_NONNULL
 195 #define ATTRIBUTE_NONNULL(m)
 196
 197 #define ATTRIBUTE_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
 198 #define ATTRIBUTE_USED __attribute__ ((__used__))
 199
 200 #include "libiberty.h"
 201 #include "pathmax.h"
 202 #include "gdb/signals.h"
 203 #include "gdb_locale.h"
 204 #include "ptid.h"
 205 #include "common-types.h"
 206 #include "common-utils.h"
 207 #include "gdb_assert.h"
 208 #include "errors.h"
 209 #include "print-utils.h"
 210 #include "common-debug.h"
 211 #include "cleanups.h"
 212 #include "common-exceptions.h"
 213 #include "gdbsupport/poison.h"
 214
 215 /* Pull in gdb::unique_xmalloc_ptr.  */
 216 #include "gdbsupport/gdb_unique_ptr.h"
 217
 218 /* sbrk on macOS is not useful for our purposes, since sbrk(0) always
 219    returns the same value.  brk/sbrk on macOS is just an emulation
 220    that always returns a pointer to a 4MB section reserved for
 221    that.  */
 222
 223 #if defined (HAVE_SBRK) && !__APPLE__
 224 #define HAVE_USEFUL_SBRK 1
 225 #endif
 226
 227 #endif /* COMMON_COMMON_DEFS_H */