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From: "fweimer at redhat dot com" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug libc/31479] Missing #include <sys/rseq.h> in sched_getcpu.c may
 result in a loss of rseq acceleration
Date: Mon, 18 Mar 2024 11:32:32 +0000
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X-Bugzilla-Product: glibc
X-Bugzilla-Component: libc
X-Bugzilla-Version: 2.35
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X-Bugzilla-Who: fweimer at redhat dot com
X-Bugzilla-Status: RESOLVED
X-Bugzilla-Resolution: FIXED
X-Bugzilla-Priority: P2
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X-Bugzilla-Target-Milestone: 2.40
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31479

Florian Weimer <fweimer at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|---                         |2.40
         Resolution|---                         |FIXED
             Status|ASSIGNED                    |RESOLVED

--- Comment #2 from Florian Weimer <fweimer at redhat dot com> ---
Fixed for 2.40 via:

commit 7a76f218677d149d8b7875b336722108239f7ee9
Author: Florian Weimer <fweimer@redhat.com>
Date:   Fri Mar 15 19:08:24 2024 +0100

    linux: Use rseq area unconditionally in sched_getcpu (bug 31479)

    Originally, nptl/descr.h included <sys/rseq.h>, but we removed that
    in commit 2c6b4b272e6b4d07303af25709051c3e96288f2d ("nptl:
    Unconditionally use a 32-byte rseq area").  After that, it was
    not ensured that the RSEQ_SIG macro was defined during sched_getcpu.c
    compilation that provided a definition.  This commit always checks
    the rseq area for CPU number information before using the other
    approaches.

    This adds an unnecessary (but well-predictable) branch on
    architectures which do not define RSEQ_SIG, but its cost is small
    compared to the system call.  Most architectures that have vDSO
    acceleration for getcpu also have rseq support.

    Fixes: 2c6b4b272e6b4d07303af25709051c3e96288f2d
    Fixes: 1d350aa06091211863e41169729cee1bca39f72f
    Reviewed-by: Arjun Shankar <arjun@redhat.com>

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