Re: [RFC] libstdc++: Make --enable-libstdcxx-backtrace=auto default to yes

[Hans-Peter Nilsson <hp@axis.com>]

I was about to enter a PR for the regression, but as you're
already aware, I'll wait 24 hours to see if this magically
goes away. :]

> On Fri, 1 Sept 2023 at 12:16, Jonathan Wakely <jwakely@redhat.com> wrote:
> >
> > On Wed, 23 Aug 2023 at 17:03, Jonathan Wakely via Libstdc++
> > <libstdc++@gcc.gnu.org> wrote:
> > >
> > > Any objections to this? It's a C++23 feture, so should be enabled by
> > > default.
> >
> > I've pushed this to trunk, so let's see what breaks!
> 
> This modules header broke on aarch64, of course:
> FAIL: g++.dg/modules/xtreme-header_b.C -std=c++2b (test for excess errors)

And others, according to testresults@ including
powerpc64le-unknown-linux-gnu, x86_64-pc-linux-gnu,
s390x-ibm-linux-gnu, m68k-unknown-linux-gnu,
pru-unknown-elf, and...cris-elf (notably, both "64-bit" and
"32-bit" configurations).

Not sure how much information you have, but for cris-elf,
g++.log shows:

FAIL: g++.dg/modules/xtreme-header_b.C -std=c++2b (test for excess errors)
Excess errors:
/obj/libstdc++-v3/include/stacktrace:202:24: error: mangling of 'constexpr std::stacktrace_entry::_M_get_info(std::string*, std::string*, int*) const::<lambda(void*, std::stacktrace_entry::uintptr_t, const char*, std::stacktrace_entry::uintptr_t, std::stacktrace_entry::uintptr_t)>::operator void (*)(void*, std::stacktrace_entry::uintptr_t, const char*, std::stacktrace_entry::uintptr_t, std::stacktrace_entry::uintptr_t)() const' as '_ZZNKSt16stacktrace_entry11_M_get_infoEPNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEES6_PiENKUlPvmPKcmmE_cvPFvS8_mSA_mmEEv' conflicts with a previous mangle
/obj/libstdc++-v3/include/stacktrace:202:24: error: mangling of 'static constexpr void std::stacktrace_entry::_M_get_info(std::string*, std::string*, int*) const::<lambda(void*, std::stacktrace_entry::uintptr_t, const char*, std::stacktrace_entry::uintptr_t, std::stacktrace_entry::uintptr_t)>::_FUN(void*, std::stacktrace_entry::uintptr_t, const char*, std::stacktrace_entry::uintptr_t, std::stacktrace_entry::uintptr_t)' as '_ZZNKSt16stacktrace_entry11_M_get_infoEPNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEES6_PiENUlPvmPKcmmE_4_FUNES8_mSA_mm' conflicts with a previous mangle
/obj/libstdc++-v3/include/stacktrace:202:24: error: mangling of 'std::stacktrace_entry::_M_get_info(std::string*, std::string*, int*) const::<lambda(void*, std::stacktrace_entry::uintptr_t, const char*, std::stacktrace_entry::uintptr_t, std::stacktrace_entry::uintptr_t)>' as '_ZZNKSt16stacktrace_entry11_M_get_infoEPNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEES6_PiENKUlPvmPKcmmE_clES8_mSA_mm' conflicts with a previous mangle

So, I *guess* it's some kind of pre-existing mangling foulup
with C++20 in the backtrace-support that just happens to be
ticked off by the module testsuite.  But you probably
already knew that.

brgds, H-P