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[Bug ld/24784] elf_x86_64_check_tls_transition should allow R_X86_64_GOT
From: |
cvs-commit at gcc dot gnu.org |
Subject: |
[Bug ld/24784] elf_x86_64_check_tls_transition should allow R_X86_64_GOTPCREL (-fno-plt) |
Date: |
Fri, 10 Mar 2023 19:53:35 +0000 |
https://sourceware.org/bugzilla/show_bug.cgi?id=24784
--- Comment #11 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot
gnu.org> ---
The master branch has been updated by Fangrui Song <maskray@sourceware.org>:
https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=d58854b6dd88e05dbf2a5d1c32c5acb7bd6ea274
commit d58854b6dd88e05dbf2a5d1c32c5acb7bd6ea274
Author: Fangrui Song <maskray@google.com>
Date: Fri Mar 10 11:53:32 2023 -0800
ld: Allow R_X86_64_GOTPCREL for call *__tls_get_addr@GOTPCREL(%rip)
_Thread_local int a;
int main() { return a; }
% gcc -fno-plt -fpic a.c -fuse-ld=bfd -Wa,-mrelax-relocations=no
/usr/bin/ld.bfd: /tmp/ccSSBgrg.o: TLS transition from R_X86_64_TLSGD to
R_X86_64_GOTTPOFF against `a' at 0xd in section `.text' failed
/usr/bin/ld.bfd: failed to set dynamic section sizes: bad value
collect2: error: ld returned 1 exit status
This commit fixes the issue.
There is an argument that the -fno-plt TLS sequence was added after
R_X86_64_GOTPCRELX was required for call, so R_X86_64_GOTPCREL was
intended to be unsupported.
Unfortunately this standpoint has caused interop difficulty: some
projects specify -mrelax-relocations=no to build relocatable object
files compatible with older linkers (e.g.
https://github.com/IHaskell/IHaskell/issues/636) or do so by accident
(e.g. https://github.com/rust-lang/rust/pull/106511 not addressed as of
today). Many uses have not been cleaned up in practice, and compiling
with -fno-plt will lead to the `TLS transition from R_X86_64_TLSGD ...`
error which is hard to reason about.
There is another argument which may be weaker but relevant to the
necessity of -mrelax-relocations=no: HWAddressSanitizer x86-64 will
likely need some assembler support to disable relaxation. Without the
support and if the compiler needs to support many gas version, the
simplest solution would be to use -Wa,-mrelax-relocations=no.
PR ld/24784
* bfd/elf64-x86-64.c (elf_x86_64_check_tls_transition): Allow
R_X86_64_GOTPCREL.
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