On Tue, Jul 15, 2025 at 3:26 AM H.J. Lu via Gcc <gcc@gcc.gnu.org> wrote: > > On Tue, Jul 15, 2025 at 8:47 AM 'Florian Weimer' via X86-64 System V > Application Binary Interface <x86-64-...@googlegroups.com> wrote: > > > > * H. J. Lu: > > > > > Compilers will never know since the build-time glibc is independent of > > > the run-time glibc. If compilers want to be 100% sure that the run-time > > > is GNU2 TLS bug-free, they can require linkers which generate the > > > GLIBC_ABI_GNU2_TLS dependency. > > > > (Such a linker requirement could be enforced by requiring that the > > linker recognizes a command option specific to GLIBC_ABI_GNU2_TLS, and > > that current linkers treat as an error.) > > > > Would such an unconditional requirement be acceptable to GCC 16? I > > don't think so. So we'd still have to design a configure option for it. > > And that requires further compiler changes. It's also not entirely > > clear how this would interact with -fuse-ld. > > > > I just don't think option (b) is trivial from a compiler perspective. > > > > It depends on what we want. If we want 100% guarantee of glibc run-time > GNU2 TLS bug-free, GCC can pass -z gnu2-tls to linker whenever GNU2 TLS > is used with glibc. It is an error if the linker doesn't support -z > gnu2-tls. We > can provide a GCC option to disable -z gnu2-tls.
I think it's the system integrators burden to ensure compatibility and thus it should be the system integrators burden to change the default. I'll note we already auto-detect --with-glibc-version in GCC (unless explicitly specified). I'm not sure what kind of decisions we base on that, but it seems reasonable to evetually use that to determine the default for the TLS ABI? Richard. > > -- > H.J.
