devel/gcc/patches/11.2.0/980-add-nostdinc++.patch

   1 From: Jonathan Wakely <jwakely@redhat.com>
   2 Date: Fri, 7 Jan 2022 15:21:03 +0000 (+0000)
   3 Subject: libstdc++: Add -nostdinc++ for c++17 sources [PR100017]
   4 X-Git-Tag: releases/gcc-11.3.0~445
   5 X-Git-Url: https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff_plain;h=01a70ccd723eb9a479186fe37c972b0d0f8676cf
   6
   7 libstdc++: Add -nostdinc++ for c++17 sources [PR100017]
   8
   9 When building a build!=host compiler, the just-built gcc can't be used
  10 to build the target libstdc++ (because it is built for the host triplet,
  11 not the build triplet). The top-level configure.ac sets up the build
  12 flags for libstdc++ (and other "raw_cxx" libs) like this:
  13
  14 GCC_TARGET_TOOL(c++ for libstdc++, RAW_CXX_FOR_TARGET, CXX,
  15                 [gcc/xgcc -shared-libgcc -B$$r/$(HOST_SUBDIR)/gcc -nostdinc++ -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/src/.libs -L$$r/$(TARGET_SUBDIR)/libstdc++-v3/libsupc++/.libs],
  16                 c++)
  17
  18 The -nostdinc++ flag is only used for the IN-TREE-TOOL, i.e. when using
  19 the just-built gcc/xgcc compiler. This means that the cross-compiler
  20 used to build libstdc++ will add its own libstdc++ headers to the
  21 include path. That results in the #include <cfenv> in
  22 src/c++17/floating_to_chars.cc and src/c++17/floating_from_chars.cc
  23 doing #include_next <fenv.h> and finding the libstdc++ fenv.h wrapper
  24 from the host compiler. Because that has the same include guard as the
  25 <fenv.h> in the libstdc++ we're trying to build, we never reach the
  26 underlying <fenv.h> from libc. That results in several errors of the
  27 form:
  28
  29 error: 'fenv_t' has not been declared in '::'
  30
  31 The most correct fix would be to add -nostdinc++ to the
  32 RAW_CXX_FOR_TARGET variable in configure.ac, or the
  33 RAW_CXX_TARGET_EXPORTS variable in Makefile.tpl.
  34
  35 Another solution would be to make the libstdc++ <fenv.h> wrapper use
  36 _GLIBCXX_INCLUDE_NEXT_C_HEADERS like our <stdlib.h> and other C header
  37 wrappers.
  38
  39 For now though, the simplest and safest solution is to just add
  40 -nostdinc++ to the CXXFLAGS used for src/c++17/*.cc, which is what this
  41 does.
  42
  43 libstdc++-v3/ChangeLog:
  44
  45         PR libstdc++/100017
  46         * src/c++17/Makefile.am (AM_CXXFLAGS): Add -nostdinc++.
  47         * src/c++17/Makefile.in: Regenerate.
  48
  49 (cherry picked from commit 4fde88e5dd152fe866a97b12e0f8229970d15cb3)
  50 ---
  51
  52 --- a/libstdc++-v3/src/c++17/Makefile.am
  53 +++ b/libstdc++-v3/src/c++17/Makefile.am
  54 @@ -79,7 +79,7 @@ endif
  55  # OPTIMIZE_CXXFLAGS on the compile line so that -O2 can be overridden
  56  # as the occasion calls for it.
  57  AM_CXXFLAGS = \
  58 -       -std=gnu++17 \
  59 +       -std=gnu++17 -nostdinc++ \
  60         $(glibcxx_lt_pic_flag) $(glibcxx_compiler_shared_flag) \
  61         $(XTEMPLATE_FLAGS) $(VTV_CXXFLAGS) \
  62         $(WARN_CXXFLAGS) $(OPTIMIZE_CXXFLAGS) $(CONFIG_CXXFLAGS) \
  63 --- a/libstdc++-v3/src/c++17/Makefile.in
  64 +++ b/libstdc++-v3/src/c++17/Makefile.in
  65 @@ -455,7 +455,7 @@ libc__17convenience_la_SOURCES = $(sourc
  66  # OPTIMIZE_CXXFLAGS on the compile line so that -O2 can be overridden
  67  # as the occasion calls for it.
  68  AM_CXXFLAGS = \
  69 -       -std=gnu++17 \
  70 +       -std=gnu++17 -nostdinc++ \
  71         $(glibcxx_lt_pic_flag) $(glibcxx_compiler_shared_flag) \
  72         $(XTEMPLATE_FLAGS) $(VTV_CXXFLAGS) \
  73         $(WARN_CXXFLAGS) $(OPTIMIZE_CXXFLAGS) $(CONFIG_CXXFLAGS) \