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 #include <gdbsupport/config.h>
  24
  25 #undef PACKAGE_NAME
  26 #undef PACKAGE
  27 #undef PACKAGE_VERSION
  28 #undef PACKAGE_STRING
  29 #undef PACKAGE_TARNAME
  30
  31 #include "gnulib/config.h"
  32
  33 /* From:
  34     https://www.gnu.org/software/gnulib/manual/html_node/stdint_002eh.html
  35
  36    "On some hosts that predate C++11, when using C++ one must define
  37    __STDC_CONSTANT_MACROS to make visible the definitions of constant
  38    macros such as INTMAX_C, and one must define __STDC_LIMIT_MACROS to
  39    make visible the definitions of limit macros such as INTMAX_MAX.".
  40
  41    And:
  42     https://www.gnu.org/software/gnulib/manual/html_node/inttypes_002eh.html
  43
  44    "On some hosts that predate C++11, when using C++ one must define
  45    __STDC_FORMAT_MACROS to make visible the declarations of format
  46    macros such as PRIdMAX."
  47
  48    Must do this before including any system header, since other system
  49    headers may include stdint.h/inttypes.h.  */
  50 #define __STDC_CONSTANT_MACROS 1
  51 #define __STDC_LIMIT_MACROS 1
  52 #define __STDC_FORMAT_MACROS 1
  53
  54 /* Some distros enable _FORTIFY_SOURCE by default, which on occasion
  55    has caused build failures with -Wunused-result when a patch is
  56    developed on a distro that does not enable _FORTIFY_SOURCE.  We
  57    enable it here in order to try to catch these problems earlier;
  58    plus this seems like a reasonable safety measure.  The check for
  59    optimization is required because _FORTIFY_SOURCE only works when
  60    optimization is enabled.  If _FORTIFY_SOURCE is already defined,
  61    then we don't do anything.  Also, on MinGW, fortify requires
  62    linking to -lssp, and to avoid the hassle of checking for
  63    that and linking to it statically, we just don't define
  64    _FORTIFY_SOURCE there.  */
  65
  66 #if (!defined _FORTIFY_SOURCE && defined __OPTIMIZE__ && __OPTIMIZE__ > 0 \
  67      && !defined(__MINGW32__))
  68 #define _FORTIFY_SOURCE 2
  69 #endif
  70
  71 /* We don't support Windows versions before XP, so we define
  72    _WIN32_WINNT correspondingly to ensure the Windows API headers
  73    expose the required symbols.
  74
  75    NOTE: this must be kept in sync with common.m4.  */
  76 #if defined (__MINGW32__) || defined (__CYGWIN__)
  77 # ifdef _WIN32_WINNT
  78 #  if _WIN32_WINNT < 0x0501
  79 #   undef _WIN32_WINNT
  80 #   define _WIN32_WINNT 0x0501
  81 #  endif
  82 # else
  83 #  define _WIN32_WINNT 0x0501
  84 # endif
  85 #endif  /* __MINGW32__ || __CYGWIN__ */
  86
  87 #include <stdarg.h>
  88 #include <stdio.h>
  89
  90 /* Include both cstdlib and stdlib.h to ensure we have standard functions
  91    defined both in the std:: namespace and in the global namespace.  */
  92 #include <cstdlib>
  93 #include <stdlib.h>
  94
  95 #include <stddef.h>
  96 #include <stdint.h>
  97 #include <string.h>
  98 #ifdef HAVE_STRINGS_H
  99 #include <strings.h>
 100 #endif
 101 #include <errno.h>
 102 #if HAVE_ALLOCA_H
 103 #include <alloca.h>
 104 #endif
 105
 106 #include "ansidecl.h"
 107 /* This is defined by ansidecl.h, but we prefer gnulib's version.  On
 108    MinGW, gnulib might enable __USE_MINGW_ANSI_STDIO, which may or not
 109    require use of attribute gnu_printf instead of printf.  gnulib
 110    checks that at configure time.  Since _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD
 111    is compatible with ATTRIBUTE_PRINTF, simply use it.  */
 112 #undef ATTRIBUTE_PRINTF
 113 #define ATTRIBUTE_PRINTF _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD
 114
 115 /* This is defined by ansidecl.h, but we disable the attribute.
 116
 117    Say a developer starts out with:
 118    ...
 119    extern void foo (void *ptr) __attribute__((nonnull (1)));
 120    void foo (void *ptr) {}
 121    ...
 122    with the idea in mind to catch:
 123    ...
 124    foo (nullptr);
 125    ...
 126    at compile time with -Werror=nonnull, and then adds:
 127    ...
 128     void foo (void *ptr) {
 129    +  gdb_assert (ptr != nullptr);
 130     }
 131    ...
 132    to catch:
 133    ...
 134    foo (variable_with_nullptr_value);
 135    ...
 136    at runtime as well.
 137
 138    Said developer then verifies that the assert works (using -O0), and commits
 139    the code.
 140
 141    Some other developer then checks out the code and accidentally writes some
 142    variant of:
 143    ...
 144    foo (variable_with_nullptr_value);
 145    ...
 146    and builds with -O2, and ... the assert doesn't trigger, because it's
 147    optimized away by gcc.
 148
 149    There's no suppported recipe to prevent the assertion from being optimized
 150    away (other than: build with -O0, or remove the nonnull attribute).  Note
 151    that -fno-delete-null-pointer-checks does not help.  A patch was submitted
 152    to improve gcc documentation to point this out more clearly (
 153    https://gcc.gnu.org/pipermail/gcc-patches/2021-July/576218.html ).  The
 154    patch also mentions a possible workaround that obfuscates the pointer
 155    using:
 156    ...
 157     void foo (void *ptr) {
 158    +  asm ("" : "+r"(ptr));
 159       gdb_assert (ptr != nullptr);
 160     }
 161    ...
 162    but that still requires the developer to manually add this in all cases
 163    where that's necessary.
 164
 165    A warning was added to detect the situation: -Wnonnull-compare, which does
 166    help in detecting those cases, but each new gcc release may indicate a new
 167    batch of locations that needs fixing, which means we've added a maintenance
 168    burden.
 169
 170    We could try to deal with the problem more proactively by introducing a
 171    gdb_assert variant like:
 172    ...
 173    void gdb_assert_non_null (void *ptr) {
 174       asm ("" : "+r"(ptr));
 175       gdb_assert (ptr != nullptr);
 176     }
 177     void foo (void *ptr) {
 178       gdb_assert_nonnull (ptr);
 179     }
 180    ...
 181    and make it a coding style to use it everywhere, but again, maintenance
 182    burden.
 183
 184    With all these things considered, for now we go with the solution with the
 185    least maintenance burden: disable the attribute, such that we reliably deal
 186    with it everywhere.  */
 187 #undef ATTRIBUTE_NONNULL
 188 #define ATTRIBUTE_NONNULL(m)
 189
 190 #if GCC_VERSION >= 3004
 191 #define ATTRIBUTE_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
 192 #else
 193 #define ATTRIBUTE_UNUSED_RESULT
 194 #endif
 195
 196 #if (GCC_VERSION > 4000)
 197 #define ATTRIBUTE_USED __attribute__ ((__used__))
 198 #else
 199 #define ATTRIBUTE_USED
 200 #endif
 201
 202 #include "libiberty.h"
 203 #include "pathmax.h"
 204 #include "gdb/signals.h"
 205 #include "gdb_locale.h"
 206 #include "ptid.h"
 207 #include "common-types.h"
 208 #include "common-utils.h"
 209 #include "gdb_assert.h"
 210 #include "errors.h"
 211 #include "print-utils.h"
 212 #include "common-debug.h"
 213 #include "cleanups.h"
 214 #include "common-exceptions.h"
 215 #include "gdbsupport/poison.h"
 216
 217 /* Pull in gdb::unique_xmalloc_ptr.  */
 218 #include "gdbsupport/gdb_unique_ptr.h"
 219
 220 /* sbrk on macOS is not useful for our purposes, since sbrk(0) always
 221    returns the same value.  brk/sbrk on macOS is just an emulation
 222    that always returns a pointer to a 4MB section reserved for
 223    that.  */
 224
 225 #if defined (HAVE_SBRK) && !__APPLE__
 226 #define HAVE_USEFUL_SBRK 1
 227 #endif
 228
 229 #endif /* COMMON_COMMON_DEFS_H */