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https://github.com/Gericom/teak-llvm.git
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f9ca13cb5f
Summary:
As of binutils 2.32, ld has a bogus TLS relaxation error when the GD/LD
code sequence using R_X86_64_GOTPCREL (instead of R_X86_64_GOTPCRELX) is
attempted to be relaxed to IE/LE (binutils PR24784). gold and lld are good.
In gcc/config/i386/i386.md, there is a configure-time check of as/ld
support and the GOT relaxation will not be used if as/ld doesn't support
it:
if (flag_plt || !HAVE_AS_IX86_TLS_GET_ADDR_GOT)
return "call\t%P2";
return "call\t{*%p2@GOT(%1)|[DWORD PTR %p2@GOT[%1]]}";
In clang, -DENABLE_X86_RELAX_RELOCATIONS=OFF is the default. The ld.bfd
bogus error can be reproduced with:
thread_local int a;
int main() { return a; }
clang -fno-plt -fpic a.cc -fuse-ld=bfd
GOTPCRELX gained relative good support in 2016, which is considered
relatively new. It is even difficult to conditionally default to
-DENABLE_X86_RELAX_RELOCATIONS=ON due to cross compilation reasons. So
work around the ld.bfd bug by only using GOT when GOTPCRELX is enabled.
Reviewers: dalias, hjl.tools, nikic, rnk
Reviewed By: nikic
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D64304
llvm-svn: 365752
40 lines
1.4 KiB
LLVM
40 lines
1.4 KiB
LLVM
; RUN: llc < %s -mtriple=i386-linux-musl -relocation-model=pic -relax-elf-relocations=true | FileCheck --check-prefixes=CHECK,X86 %s
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; RUN: llc < %s -mtriple=x86_64-linux-musl -relocation-model=pic -relax-elf-relocations=true | FileCheck --check-prefixes=CHECK,X64 %s
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;; If GOTPCRELX is disabled, don't use GOT for __tls_get_addr to work around
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;; a ld.bfd bug (binutils PR24784).
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; RUN: llc < %s -mtriple=i386-linux-musl -relocation-model=pic | FileCheck --check-prefixes=CHECK,X86-PLT %s
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; RUN: llc < %s -mtriple=x86_64-linux-musl -relocation-model=pic | FileCheck --check-prefixes=CHECK,X64-PLT %s
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@gd = thread_local global i32 0
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@ld = internal thread_local global i32 0
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define i32* @get_gd() {
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entry:
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; CHECK-LABEL: get_gd:
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; X86: leal gd@TLSGD(%ebx), %eax
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; X86: calll *___tls_get_addr@GOT(%ebx)
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; X86-PLT: calll ___tls_get_addr@PLT
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; X64: leaq gd@TLSGD(%rip), %rdi
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; X64: callq *__tls_get_addr@GOTPCREL(%rip)
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; X64-PLT: callq __tls_get_addr@PLT
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ret i32* @gd
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}
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define i32* @get_ld() {
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; FIXME: This function uses a single thread-local variable, we might want to fall back to general-dynamic.
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; CHECK-LABEL: get_ld:
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; X86: leal ld@TLSLDM(%ebx), %eax
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; X86: calll *___tls_get_addr@GOT(%ebx)
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; X86-PLT: calll ___tls_get_addr@PLT
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; X64: leaq ld@TLSLD(%rip), %rdi
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; X64: callq *__tls_get_addr@GOTPCREL(%rip)
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; X64-PLT: callq __tls_get_addr@PLT
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ret i32* @ld
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}
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!llvm.module.flags = !{!1}
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!1 = !{i32 7, !"RtLibUseGOT", i32 1}
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