Re: [PATCH 0/2] m68k: Add vDSO support for TLS and clock_gettime64

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From: "Andreas K. Huettel" <[email protected]>
To: [email protected]
Date: Thu, 08 Jan 2026 22:46:12 +0100
Message-ID: <2770965.ElGaqSPkdT@pinacolada>
Organization: Gentoo Linux
In-Reply-To: <[email protected]>
References: <[email protected]>
MIME-Version: 1.0

Am Donnerstag, 8. Januar 2026, 07:18:20 Mitteleurop=C3=A4ische Normalzeit s=
chrieb Stefan:
> This series adds vDSO support for m68k, enabling userspace to access
> the thread pointer and clock_gettime64 without syscall overhead.

After the release only please (given other concerns are addressed)

>=20
> 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.
>=20
> 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.
>=20
> 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.
>=20
> Both changes include fallback paths for older kernels that lack vDSO
> support.
>=20
> Performance Results (QEMU Quadra 800)
> -------------------------------------
> Before (syscall):     ~2057 ns/call
> After (vDSO):         ~675 ns/call
> Improvement:          ~3x faster
>=20
> Tested on qemu-system-m68k with Linux 6.18 (Debian/m68k).
>=20
> Stefan Reinauer (2):
>   m68k: Use vDSO for thread pointer access
>   m68k: Enable vDSO clock_gettime64
>=20
>  sysdeps/unix/sysv/linux/m68k/m68k-helpers.c | 77 ++++++++++++++++++++-
>  sysdeps/unix/sysv/linux/m68k/sysdep.h       |  7 ++
>  2 files changed, 83 insertions(+), 1 deletion(-)
>=20
>=20


=2D-=20
Andreas K. H=C3=BCttel
[email protected]
Gentoo Linux developer
(council, toolchain, base-system, perl, libreoffice)
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