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gcc: Fix canadian cross building on older hosts

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GCC 11+ requires compiler being used to support C++11 standard [1].
And while GCC starting from 6.x has C++11 support enabled by default [2],
older versions need to be forced to implement it with "-std=gnu++11" and luckily
GCC's build-system takes care of that:

 1. For ${host} compiler - [1]
 2. For ${build} compiler - [3, 4]

In a nutshell the configure script tries a couple of options and the one which
helps to build a test source gets appended to CXX (not CXXFLAGS!),
so on say CentOS 7.x with GCC 4.8.5 during cross-compilation of GCC
CXX="x86_64-build_pc-linux-gnu-g++ -std=gnu++11". And all is good.

But in case of canadian cross due to [5] we for some reason* force set
CXX_FOR_BUILD with just a compiler name, effectively overriding all the
magic done by GCC's internals described above.

This leads to a compilation failures like that:
------------------------------------->8----------------------------------
[ALL  ]    In file included from /usr/include/c++/4.8.2/type_traits:35:0,
[ALL  ]                     from .../HOST-x86_64-apple-darwin14/arc-gcc11-elf/src/gcc/gcc/system.h:244,
[ALL  ]                     from .../HOST-x86_64-apple-darwin14/arc-gcc11-elf/src/gcc/gcc/gengtype.c:26:
[ERROR]    /usr/include/c++/4.8.2/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support is currently experimental, and must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
[ALL  ]     #error This file requires compiler and library support for the   ^
------------------------------------->8----------------------------------

* my guess that [5] was done because back in the day indeed we used to have
"--build=${CT_BUILD} --host=${CT_HOST}" in do_cc_core(). But now after [6]
this is no longer necessary as we use "--build=${CT_BUILD} --host=${CT_BUILD}"
and all is safe and clean. So yet another old quirk goes away - hooray!

[1] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=5329b59a2e13dabbe2038af0fe2e3cf5fc7f98ed
[2] https://gcc.gnu.org/gcc-6/changes.html
[3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96612
[4] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=7ffcf5d61174dda1f39a623e15f7e5d6b98bbafc
[5] 9c6c090d7b
[6] 08161250ed

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
This commit is contained in:
Alexey Brodkin 2021-09-06 23:01:44 -07:00
parent 4de586cd2e
commit 5c5b4df6d3
1 changed files with 1 additions and 13 deletions
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14
scripts/build/cc/gcc.sh
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@ -696,20 +696,8 @@ do_gcc_core_backend() {
libgcc_rule="libgcc.mvars"
core_targets=( gcc target-libgcc )
# On bare metal and canadian build the host-compiler is used when
# actually the build-system compiler is required. Choose the correct
# compilers for canadian build and use the defaults on other
# configurations.
if [ "${CT_BARE_METAL},${CT_CANADIAN}" = "y,y" ]; then
repair_cc="CC_FOR_BUILD=${CT_BUILD}-gcc \
CXX_FOR_BUILD=${CT_BUILD}-g++ \
GCC_FOR_TARGET=${CT_TARGET}-${CT_CC}"
else
repair_cc=""
fi
CT_DoExecLog ALL make ${CT_JOBSFLAGS} -C gcc ${libgcc_rule}
CT_DoExecLog ALL make ${CT_JOBSFLAGS} -C gcc ${libgcc_rule} \
${repair_cc}
sed -r -i -e 's@-lc@@g' gcc/${libgcc_rule}
else # build_libgcc
core_targets=( gcc )