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From: "unlvsur at live dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug libstdc++/100017] [11/12 regression] error: 'fenv_t' has not
 been declared in '::' -- canadian compilation fails
Date: Thu, 06 Jan 2022 17:24:45 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D100017

--- Comment #59 from cqwrteur <unlvsur at live dot com> ---
(In reply to Jakub Jelinek from comment #57)
> I don't see how the patch could be correct.
> Looking at RAW_CXX_FOR_TARGET in configure, I see:
> (starting with the line you're proposing to change):
> RAW_CXX_FOR_TARGET=3D"$CXX_FOR_TARGET"
> ...
> { $as_echo "$as_me:${as_lineno-$LINENO}: checking where to find the target
> c++ for libstdc++" >&5
> $as_echo_n "checking where to find the target c++ for libstdc++... " >&6;=
 }
> if test "x${build}" !=3D "x${host}" ; then
>   if expr "x$RAW_CXX_FOR_TARGET" : "x/" > /dev/null; then
>     # We already found the complete path
>     ac_dir=3D`dirname $RAW_CXX_FOR_TARGET`
>     { $as_echo "$as_me:${as_lineno-$LINENO}: result: pre-installed in
> $ac_dir" >&5
> $as_echo "pre-installed in $ac_dir" >&6; }
>   else
>     # Canadian cross, just use what we found
>     { $as_echo "$as_me:${as_lineno-$LINENO}: result: pre-installed" >&5
> $as_echo "pre-installed" >&6; }
>   fi
> else
>=20
> So, if CXX_FOR_TARGET starts with /, e.g. /opt/gcc-11.1/bin/g++ , then
> the above will use dirname /opt/gcc-11.1/bin/g++ and set ac_dir to
> /opt/gcc-11.1/bin
> But with the proposed change, $RAW_CXX_FOR_TARGET will be
> /opt/gcc-11.1/bin/g++ -nostdinc++ and dirname will fail miserably and not
> set ac_dir to anything:
> dirname /opt/gcc-11.1/bin/g++ -nostdinc++
> dirname: invalid option -- 'n'
> Try 'dirname --help' for more information.

So is this just an issue to libstdc++'s configure script only? Why the auto=
tool
fails to find header files?=