gdbsupport/common-defs.h

   1 /* Common definitions.
   2
   3    Copyright (C) 1986-2022 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 #if defined (__MINGW32__) || defined (__CYGWIN__)
  75 # ifdef _WIN32_WINNT
  76 #  if _WIN32_WINNT < 0x0501
  77 #   undef _WIN32_WINNT
  78 #   define _WIN32_WINNT 0x0501
  79 #  endif
  80 # else
  81 #  define _WIN32_WINNT 0x0501
  82 # endif
  83 #endif  /* __MINGW32__ || __CYGWIN__ */
  84
  85 #include <stdarg.h>
  86 #include <stdio.h>
  87
  88 /* Include both cstdlib and stdlib.h to ensure we have standard functions
  89    defined both in the std:: namespace and in the global namespace.  */
  90 #include <cstdlib>
  91 #include <stdlib.h>
  92
  93 #include <stddef.h>
  94 #include <stdint.h>
  95 #include <string.h>
  96 #ifdef HAVE_STRINGS_H
  97 #include <strings.h>    /* for strcasecmp and strncasecmp */
  98 #endif
  99 #include <errno.h>
 100 #if HAVE_ALLOCA_H
 101 #include <alloca.h>
 102 #endif
 103
 104 #include "ansidecl.h"
 105 /* This is defined by ansidecl.h, but we prefer gnulib's version.  On
 106    MinGW, gnulib might enable __USE_MINGW_ANSI_STDIO, which may or not
 107    require use of attribute gnu_printf instead of printf.  gnulib
 108    checks that at configure time.  Since _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD
 109    is compatible with ATTRIBUTE_PRINTF, simply use it.  */
 110 #undef ATTRIBUTE_PRINTF
 111 #define ATTRIBUTE_PRINTF _GL_ATTRIBUTE_FORMAT_PRINTF_STANDARD
 112
 113 /* This is defined by ansidecl.h, but we disable the attribute.
 114
 115    Say a developer starts out with:
 116    ...
 117    extern void foo (void *ptr) __atttribute__((nonnull (1)));
 118    void foo (void *ptr) {}
 119    ...
 120    with the idea in mind to catch:
 121    ...
 122    foo (nullptr);
 123    ...
 124    at compile time with -Werror=nonnull, and then adds:
 125    ...
 126     void foo (void *ptr) {
 127    +  gdb_assert (ptr != nullptr);
 128     }
 129    ...
 130    to catch:
 131    ...
 132    foo (variable_with_nullptr_value);
 133    ...
 134    at runtime as well.
 135
 136    Said developer then verifies that the assert works (using -O0), and commits
 137    the code.
 138
 139    Some other developer then checks out the code and accidentally writes some
 140    variant of:
 141    ...
 142    foo (variable_with_nullptr_value);
 143    ...
 144    and builds with -O2, and ... the assert doesn't trigger, because it's
 145    optimized away by gcc.
 146
 147    There's no suppported recipe to prevent the assertion from being optimized
 148    away (other than: build with -O0, or remove the nonnull attribute).  Note
 149    that -fno-delete-null-pointer-checks does not help.  A patch was submitted
 150    to improve gcc documentation to point this out more clearly (
 151    https://gcc.gnu.org/pipermail/gcc-patches/2021-July/576218.html ).  The
 152    patch also mentions a possible workaround that obfuscates the pointer
 153    using:
 154    ...
 155     void foo (void *ptr) {
 156    +  asm ("" : "+r"(ptr));
 157       gdb_assert (ptr != nullptr);
 158     }
 159    ...
 160    but that still requires the developer to manually add this in all cases
 161    where that's necessary.
 162
 163    A warning was added to detect the situation: -Wnonnull-compare, which does
 164    help in detecting those cases, but each new gcc release may indicate a new
 165    batch of locations that needs fixing, which means we've added a maintenance
 166    burden.
 167
 168    We could try to deal with the problem more proactively by introducing a
 169    gdb_assert variant like:
 170    ...
 171    void gdb_assert_non_null (void *ptr) {
 172       asm ("" : "+r"(ptr));
 173       gdb_assert (ptr != nullptr);
 174     }
 175     void foo (void *ptr) {
 176       gdb_assert_nonnull (ptr);
 177     }
 178    ...
 179    and make it a coding style to use it everywhere, but again, maintenance
 180    burden.
 181
 182    With all these things considered, for now we go with the solution with the
 183    least maintenance burden: disable the attribute, such that we reliably deal
 184    with it everywhere.  */
 185 #undef ATTRIBUTE_NONNULL
 186 #define ATTRIBUTE_NONNULL(m)
 187
 188 #if GCC_VERSION >= 3004
 189 #define ATTRIBUTE_UNUSED_RESULT __attribute__ ((__warn_unused_result__))
 190 #else
 191 #define ATTRIBUTE_UNUSED_RESULT
 192 #endif
 193
 194 #include "libiberty.h"
 195 #include "pathmax.h"
 196 #include "gdb/signals.h"
 197 #include "gdb_locale.h"
 198 #include "ptid.h"
 199 #include "common-types.h"
 200 #include "common-utils.h"
 201 #include "gdb_assert.h"
 202 #include "errors.h"
 203 #include "print-utils.h"
 204 #include "common-debug.h"
 205 #include "cleanups.h"
 206 #include "common-exceptions.h"
 207 #include "gdbsupport/poison.h"
 208
 209 #define EXTERN_C extern "C"
 210 #define EXTERN_C_PUSH extern "C" {
 211 #define EXTERN_C_POP }
 212
 213 /* Pull in gdb::unique_xmalloc_ptr.  */
 214 #include "gdbsupport/gdb_unique_ptr.h"
 215
 216 /* sbrk on macOS is not useful for our purposes, since sbrk(0) always
 217    returns the same value.  brk/sbrk on macOS is just an emulation
 218    that always returns a pointer to a 4MB section reserved for
 219    that.  */
 220
 221 #if defined (HAVE_SBRK) && !__APPLE__
 222 #define HAVE_USEFUL_SBRK 1
 223 #endif
 224
 225 #endif /* COMMON_COMMON_DEFS_H */