> On 22 Dec 2022, at 21:15, Jason Merrill <ja...@redhat.com> wrote:
>
> On 12/4/22 11:30, Iain Sandoe wrote:
>> This fixes a long-standing problem on Darwin where we cannot independently
>> set
>> -static-libstdc++ because the flag gets stripped by the g++ driver.
>> This patch is essentially the same as the one used for the 'D' driver and has
>> been in local use for some time. It has also been tested on Linux.
>> OK for master?
>> backports?
>> thanks
>> Iain
>> -- >8 --
>> The current implementation for swapping between the static and shared c++
>> runtimes relies on the static linker supporting Bstatic/dynamic which is
>> not available for every target (Darwin's linker does not support this).
>> Specs substitution (%s) is an alternative solution for this (which is what
>> Darwin uses for Fortran, D and Objective-C). However, specs substitution
>> requires that the '-static-libstdc++' be preserved in the driver's command
>> line. The patch here arranges for this to be done when the configuration
>> determines that linker support for Bstatic/dynamic is missing.
>
> Would it work to define LIBSTDCXX_STATIC instead?
Not without modifying the build of libstdc++. When Darwin’s linker sees a
convenience library with the
same name as a shared one, it will pick the shared one, so we would have to
modify the build of libstdc++
to make the library named libstdc++-static.a or so (that was essentially what
the Apple gcc-4.2.1 impl.
did AFAIR).
> If not, the patch is OK.
Thanks.
>
> Really there should be a way for lang_specific_driver to mark a flag as
> "validated" rather than prune it.
Yes - especially since we now already three drivers (c++, d, gm2) that need to
do the same stuff for
handing libstdc++.
Iain
>
>> Signed-off-by: Iain Sandoe <i...@sandoe.co.uk>
>> gcc/cp/ChangeLog:
>> * g++spec.cc (lang_specific_driver): Preserve -static-libstdc++ in
>> the driver command line for targets without -Bstatic/dynamic support
>> in their static linker.
>> ---
>> gcc/cp/g++spec.cc | 5 +++++
>> 1 file changed, 5 insertions(+)
>> diff --git a/gcc/cp/g++spec.cc b/gcc/cp/g++spec.cc
>> index 3d3b042dd56..f95d7965355 100644
>> --- a/gcc/cp/g++spec.cc
>> +++ b/gcc/cp/g++spec.cc
>> @@ -234,7 +234,12 @@ lang_specific_driver (struct cl_decoded_option
>> **in_decoded_options,
>> case OPT_static_libstdc__:
>> library = library >= 0 ? 2 : library;
>> +#ifdef HAVE_LD_STATIC_DYNAMIC
>> + /* Remove -static-libstdc++ from the command only if target supports
>> + LD_STATIC_DYNAMIC. When not supported, it is left in so that a
>> + back-end target can use outfile substitution. */
>> args[i] |= SKIPOPT;
>> +#endif
>> break;
>> case OPT_stdlib_:
>
