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From: "cvs-commit at gcc dot gnu.org" <sourceware-bugzilla@sourceware.org>
To: glibc-bugs@sourceware.org
Subject: [Bug dynamic-link/31185] Incorrect thread point access in
 _dl_tlsdesc_undefweak and _dl_tlsdesc_dynamic
Date: Fri, 22 Dec 2023 13:37:41 +0000
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https://sourceware.org/bugzilla/show_bug.cgi?id=3D31185

--- Comment #1 from Sourceware Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by H.J. Lu <hjl@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=3Dglibc.git;h=3D81be2a61dafc168327c=
1639e97b6dae128c7ccf3

commit 81be2a61dafc168327c1639e97b6dae128c7ccf3
Author: H.J. Lu <hjl.tools@gmail.com>
Date:   Wed Dec 20 19:42:12 2023 -0800

    x86-64: Fix the tcb field load for x32 [BZ #31185]

    _dl_tlsdesc_undefweak and _dl_tlsdesc_dynamic access the thread pointer
    via the tcb field in TCB:

    _dl_tlsdesc_undefweak:
            _CET_ENDBR
            movq    8(%rax), %rax
            subq    %fs:0, %rax
            ret

    _dl_tlsdesc_dynamic:
            ...
            subq    %fs:0, %rax
            movq    -8(%rsp), %rdi
            ret

    Since the tcb field in TCB is a pointer, %fs:0 is a 32-bit location,
    not 64-bit. It should use "sub %fs:0, %RAX_LP" instead.  Since
    _dl_tlsdesc_undefweak returns ptrdiff_t and _dl_make_tlsdesc_dynamic
    returns void *, RAX_LP is appropriate here for x32 and x86-64.  This
    fixes BZ #31185.

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