This series adds vDSO support for m68k, enabling userspace to access the thread pointer and clock_gettime64 without syscall overhead.
The m68k vDSO provides a data page mapped at a fixed offset from the ELF header (passed via AT_SYSINFO_EHDR). The kernel maintains the thread pointer and timing data in this page, updating them on context switches. Patch 1 optimizes __m68k_read_tp() to read the thread pointer directly from the vDSO data page instead of using the get_thread_area syscall. This significantly reduces overhead for TLS access, which is a frequent operation in threaded applications. Patch 2 enables the vDSO clock_gettime64 by defining HAVE_CLOCK_GETTIME64_VSYSCALL along with the necessary VDSO_NAME and VDSO_HASH for symbol lookup. This allows glibc to use the kernel-provided __vdso_clock_gettime64 for fast time retrieval. Both changes include fallback paths for older kernels that lack vDSO support. Performance Results (QEMU Quadra 800) ------------------------------------- Before (syscall): ~2057 ns/call After (vDSO): ~675 ns/call Improvement: ~3x faster Tested on qemu-system-m68k with Linux 6.18 (Debian/m68k). Stefan Reinauer (2): m68k: Use vDSO for thread pointer access m68k: Enable vDSO clock_gettime64 sysdeps/unix/sysv/linux/m68k/m68k-helpers.c | 77 ++++++++++++++++++++- sysdeps/unix/sysv/linux/m68k/sysdep.h | 7 ++ 2 files changed, 83 insertions(+), 1 deletion(-) -- 2.51.0
