On Wed, Apr 22, 2026 at 06:42:54PM +0100, Leo Yan wrote: > Building on Debian sid with GCC 15 fails: > > CC libc-gcs > libc-gcs.c: In function 'ptrace_read_write': > libc-gcs.c:142:25: error: storage size of 'child_gcs' isn't known > 142 | struct user_gcs child_gcs; > | ^~~~~~~~~ > libc-gcs.c:142:25: warning: unused variable 'child_gcs' [-Wunused-variable] > > For GCC-15, NT_ARM_GCS is defined in the libc header, causing gcs-util.h > to skip its fallback definition of struct user_gcs. This leads to the > compiler error. > > Fix this by including <asm/ptrace.h> to provide the proper definition.
This is not caused by GCC-15 as it doesn't provide these headers. AFAICT on Debian we have NT_ARM_GCS coming from glibc and user_gcs from the kernel asm/ptrace.h uapi header (linux-libc-dev). We also have NT_ARM_GCS in linux/elf.h as part of the kernel headers. While the kernel exposed the macro and structure in the same commit, I don't think it is required distros to align the glibc macro with the linux headers. Glibc does not even use the kernel's linux/elf.h for the macros, it just adds the definitions when they turn up in a released kernel. So you can have a glibc that defines NT_ARM_GCS but a linux-libc-dev package that is not up to date to include struct user_gcs. I think a better fix is to always define struct user_gcs and only conditionally define NT_ARM_GCS (IOW, move the #endif higher). -- Catalin
