On Tue, Feb 18, 2025 at 8:26 PM Uros Bizjak <ubiz...@gmail.com> wrote:
>
> On Tue, Feb 18, 2025 at 8:23 PM Richard Biener <rguent...@suse.de> wrote:
> >
> >
> >
> > > Am 18.02.2025 um 20:07 schrieb Roman Kagan <rka...@amazon.de>:
> > >
> > > On Tue, Feb 18, 2025 at 07:17:24PM +0100, Uros Bizjak wrote:
> > >>> On Mon, Feb 17, 2025 at 6:19 PM Roman Kagan <rka...@amazon.de> wrote:
> > >>>
> > >>> On Thu, Jan 02, 2025 at 04:32:17PM +0100, Roman Kagan wrote:
> > >>>> When gcc is built for x86_64-linux-musl target, stack unwinding from
> > >>>> within signal handler stops at the innermost signal frame. The reason
> > >>>> for this behaviro is that the signal trampoline is not accompanied with
> > >>>> appropiate CFI directives, and the fallback path in libgcc to recognize
> > >>>> it by the code sequence is only enabled for glibc except 2.0. The
> > >>>> latter is motivated by the lack of sys/ucontext.h in that glibc
> > >>>> version.
> > >>>>
> > >>>> Given that all relevant libc-s ship sys/ucontext.h for over a decade,
> > >>>> and that other arches aren't shy of unconditionally using it, follow
> > >>>> suit and remove the preprocessor condition, too.
> > >>
> > >> "Relevant libc"-s for x86 linux are LIBC_GLIBC, LIBC_UCLIBC,
> > >> LIBC_BIONIC and LIBC_MUSL. As far as glibc is concerned, the latest
> > >> glibc 2.0.x version was released in 1997 [1], so I guess we can remove
> > >> the condition for version 2.0. Based on your claim, the other
> > >> mentioned libcs also provide the required header for a long time.
> > >
> > > Ah, good point, for completeness I should've supplied evidence from
> > > their respective git repos, here you go:
> > >
> > > uclibc(-ng):
> > > libc/sysdeps/linux/i386/sys/ucontext.h
> > >
> > > commit 9cee42f10dbc5b33866ff137b926a74abd7c1a5b
> > > Author: Eric Andersen <ander...@codepoet.org>
> > > Date: Fri Mar 1 20:46:26 2002 +0000
> > >
> > > Major rework of the include files to eliminate redundancy
> > > and to better support each arch. This is a really big patch...
> > > -Erik
> > >
> > > libc/sysdeps/linux/i386/sys/ucontext.h
> > >
> > > commit 1fef64b22811709b2e640d341237bce1c8081203
> > > Author: Mike Frysinger <vap...@gentoo.org>
> > > Date: Tue Feb 15 01:27:10 2005 +0000
> > >
> > > headers for x86_64
> > >
> > > bionic:
> > > libc/include/sys/ucontext.h
> > >
> > > commit e61d106008f7d77fa1c0de43ac27311320225135
> > > Author: Pavel Chupin <pavel.v.chu...@intel.com>
> > > Date: Mon Jan 27 17:56:43 2014 +0400
> > >
> > > Add x86_64 ucontext.h for better compatibility
> > >
> > > As suggested here:
> > > https://android-review.googlesource.com/#/c/71267/
> > > it may be used for x86_64 libunwind enabling.
> > >
> > > Change-Id: I21623261a48ea7099e030d33932556e294d226ff
> > > Signed-off-by: Pavel Chupin <pavel.v.chu...@intel.com>
> > >
> > > commit 677a07cb9a3f5964e9ead4d37b9f775d971c61e0
> > > Author: Elliott Hughes <e...@google.com>
> > > Date: Wed Jan 29 16:46:00 2014 -0800
> > >
> > > Add x86 <sys/ucontext.h>.
> > >
> > > Change-Id: I43e72604f7a932f134733b78094b577415a5edb7
> > >
> > > musl:
> > > arch/i386/bits/signal.h
> > > arch/x86_64/bits/signal.h
> > > include/ucontext.h
> > >
> > > commit ad2fe25041622b6cf426b0f98af0e52c2c9727f6
> > > Author: Rich Felker <dal...@aerifal.cx>
> > > Date: Fri Feb 18 22:03:03 2011 -0500
> > >
> > > support the ugly and deprecated ucontext and sigcontext header
> > > stuff...
> > >
> > > only the structures, not the functions from ucontext.h, are
> > > supported
> > > at this point. the main goal of this commit is to make modern gcc
> > > with
> > > dwarf2 unwinding build without errors.
> > >
> > > honestly, it probably doesn't matter how we define these as long as
> > > they have members with the right names to prevent errors while
> > > compiling libgcc. the only time they will be used is for
> > > propagating
> > > exceptions across signal-handler boundaries, which invokes
> > > undefined
> > > behavior anyway. but as-is, they're probably correct and may be
> > > useful
> > > to various low-level applications dealing with virtualization, jit
> > > code generation, and so on...
> > >
> > >> I have no objection to the patch, but I think that this patch is a bit
> > >> late for gcc-15 and should be committed early in the gcc-16
> > >> development cycle. But let's hear release managers (CC'd).
> >
> > It’s fine for 15, or rather I’m leaving it for you to decide.
>
> OK, based on the above research, I'll commit it to gcc-15.
Committed as e129b8d7682c9a6c4d874f58de142543d3804169
with the following ChangeLog entry:
libgcc/ChangeLog:
* config/i386/linux-unwind.h: Remove preprocessor
condition to enable fallback path for all libc-s.
Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.
Thanks,
Uros.
