Re: GDB 17 build failure with musl

[Chris Packham via Gdb <gdb@sourceware.org>]

On Wed, Feb 4, 2026 at 5:11 PM Thiago Jung Bauermann
<thiago.bauermann@linaro.org> wrote:
>
> Chris Packham <judge.packham@gmail.com> writes:
>
> > On Tue, Feb 3, 2026 at 4:10 PM Thiago Jung Bauermann
> > <thiago.bauermann@linaro.org> wrote:
> >>
> >> Do you have reproduction instructions for this problem? I'd like to
> >> experiment a bit and see if I can come up with a solution.
> >
> > The only reproduction I have right now is to build crosstool-ng then
> > use ct-ng to build the aarch64-unknown-linux-musl sample. You'd need
> > to build from crosstool-ng commit be7fafbc7b6435 as I ended up
> > reverting the update for now to unblock some builds.
> >
> > For the intrepid:
> >
> >   git clone https://github.com/crosstool-ng/crosstool-ng.git
> >   cd crosstool-ng
> >   git checkout -B gdb-17-build  be7fafbc7b6435
> >   ./bootstrap && ./configure --enable-local && make
> >   ./ct-ng aarch64-unknown-linux-musl
> >   ./ct-ng build
> >   # go get a coffee this part can take a while
> >
> > I have been meaning to come up with a better reproduction. At the very
> > least you could disable the gdb options in ./ct-ng menuconfig and use
> > the resulting toolchain & sysroot to build gdb rather than having to
> > sit through a full build to try something out (ct-ng does also have
> > various options for restarting a build from a particular step).
>
> Thank you! This got me started. I suspect I'll have to add a configure
> test for availability of struct user_gcs. I don't see any macro in
> <asm/ptrace.h> itself which is correlated to the presence of that
> struct. I'll let you know when I have a patch.
>

I came to the same conclusion although I had a hard time getting the
configure result into a place that could actually use it. If it helps
here is the configure check I wrote

# Check for `struct user_gcs`
AC_CACHE_CHECK(
  [for struct user_gcs],
  [gdb_cv_struct_user_gcs],
  [AC_COMPILE_IFELSE(
     [AC_LANG_PROGRAM(
        [#include <sys/ptrace.h>
         #include <asm/ptrace.h>],
        [struct user_gcs u;]
      )],
     [gdb_cv_struct_user_gcs=yes],
     [gdb_cv_struct_user_gcs=no]
  )]
)
if test "$gdb_cv_struct_user_gcs" = yes; then
  AC_DEFINE(HAVE_STRUCT_USER_GCS, 1,
            [Define to 1 if your system has struct user_gcs.])
fi

>
> > I actually suspect you could probably see the problem on a musl based
> > distro on an aarch64 host (or docker multiarch) but I haven't looked
> > into that.
>
> Ah, that's true. I'll also test on Alpine Linux to make sure the patch
> works there.
>
> --
> Thiago