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- From: Jonathan Wakely <jwakely@redhat.com>
- Date: Fri, 7 Jan 2022 15:21:03 +0000 (+0000)
- Subject: libstdc++: Add -nostdinc++ for c++17 sources [PR100017]
- X-Git-Tag: releases/gcc-11.3.0~445
- X-Git-Url: https://gcc.gnu.org/git/?p=gcc.git;a=commitdiff_plain;h=01a70ccd723eb9a479186fe37c972b0d0f8676cf
-
- libstdc++: Add -nostdinc++ for c++17 sources [PR100017]
-
- When building a build!=host compiler, the just-built gcc can't be used
- to build the target libstdc++ (because it is built for the host triplet,
- not the build triplet). The top-level configure.ac sets up the build
- flags for libstdc++ (and other "raw_cxx" libs) like this:
-
- GCC_TARGET_TOOL(c++ for libstdc++, RAW_CXX_FOR_TARGET, CXX,
- [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],
- c++)
-
- The -nostdinc++ flag is only used for the IN-TREE-TOOL, i.e. when using
- the just-built gcc/xgcc compiler. This means that the cross-compiler
- used to build libstdc++ will add its own libstdc++ headers to the
- include path. That results in the #include <cfenv> in
- src/c++17/floating_to_chars.cc and src/c++17/floating_from_chars.cc
- doing #include_next <fenv.h> and finding the libstdc++ fenv.h wrapper
- from the host compiler. Because that has the same include guard as the
- <fenv.h> in the libstdc++ we're trying to build, we never reach the
- underlying <fenv.h> from libc. That results in several errors of the
- form:
-
- error: 'fenv_t' has not been declared in '::'
-
- The most correct fix would be to add -nostdinc++ to the
- RAW_CXX_FOR_TARGET variable in configure.ac, or the
- RAW_CXX_TARGET_EXPORTS variable in Makefile.tpl.
-
- Another solution would be to make the libstdc++ <fenv.h> wrapper use
- _GLIBCXX_INCLUDE_NEXT_C_HEADERS like our <stdlib.h> and other C header
- wrappers.
-
- For now though, the simplest and safest solution is to just add
- -nostdinc++ to the CXXFLAGS used for src/c++17/*.cc, which is what this
- does.
-
- libstdc++-v3/ChangeLog:
-
- PR libstdc++/100017
- * src/c++17/Makefile.am (AM_CXXFLAGS): Add -nostdinc++.
- * src/c++17/Makefile.in: Regenerate.
-
- (cherry picked from commit 4fde88e5dd152fe866a97b12e0f8229970d15cb3)
- ---
-
- --- a/libstdc++-v3/src/c++17/Makefile.am
- +++ b/libstdc++-v3/src/c++17/Makefile.am
- @@ -79,7 +79,7 @@ endif
- # OPTIMIZE_CXXFLAGS on the compile line so that -O2 can be overridden
- # as the occasion calls for it.
- AM_CXXFLAGS = \
- - -std=gnu++17 \
- + -std=gnu++17 -nostdinc++ \
- $(glibcxx_lt_pic_flag) $(glibcxx_compiler_shared_flag) \
- $(XTEMPLATE_FLAGS) $(VTV_CXXFLAGS) \
- $(WARN_CXXFLAGS) $(OPTIMIZE_CXXFLAGS) $(CONFIG_CXXFLAGS) \
- --- a/libstdc++-v3/src/c++17/Makefile.in
- +++ b/libstdc++-v3/src/c++17/Makefile.in
- @@ -455,7 +455,7 @@ libc__17convenience_la_SOURCES = $(sourc
- # OPTIMIZE_CXXFLAGS on the compile line so that -O2 can be overridden
- # as the occasion calls for it.
- AM_CXXFLAGS = \
- - -std=gnu++17 \
- + -std=gnu++17 -nostdinc++ \
- $(glibcxx_lt_pic_flag) $(glibcxx_compiler_shared_flag) \
- $(XTEMPLATE_FLAGS) $(VTV_CXXFLAGS) \
- $(WARN_CXXFLAGS) $(OPTIMIZE_CXXFLAGS) $(CONFIG_CXXFLAGS) \
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