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

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

[H.J. Lu]

https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=81be2a61dafc168327c1639e97b6dae128c7ccf3

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.

Diff:
---
 sysdeps/x86_64/dl-tlsdesc.S | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/sysdeps/x86_64/dl-tlsdesc.S b/sysdeps/x86_64/dl-tlsdesc.S
index c4823547d7..4579424bf7 100644
--- a/sysdeps/x86_64/dl-tlsdesc.S
+++ b/sysdeps/x86_64/dl-tlsdesc.S
@@ -61,7 +61,7 @@ _dl_tlsdesc_return:
 _dl_tlsdesc_undefweak:
 	_CET_ENDBR
 	movq	8(%rax), %rax
-	subq	%fs:0, %rax
+	sub	%fs:0, %RAX_LP
 	ret
 	cfi_endproc
 	.size	_dl_tlsdesc_undefweak, .-_dl_tlsdesc_undefweak
@@ -116,7 +116,7 @@ _dl_tlsdesc_dynamic:
 	addq	TLSDESC_MODOFF(%rdi), %rax
 .Lret:
 	movq	-16(%rsp), %rsi
-	subq	%fs:0, %rax
+	sub	%fs:0, %RAX_LP
 	movq	-8(%rsp), %rdi
 	ret
 .Lslow: