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[ELF][MIPS] Fix TLS GOT entries for local symbols in shared libraries

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Summary:
Previously LLD would not add any dynamic relocations and write a module
index of 1 which is not correct for the shared library case.
This can happen when a thread-local global variable is marked as local with
a version script. With this change I am now able to link all of the FreeBSD
base system for MIPS64 with LLD.

Differential Revision: https://reviews.llvm.org/D48002

llvm-svn: 334483
This commit is contained in:
Alexander Richardson
2018-06-12 08:00:38 +00:00
parent 88c230265b
commit 127176e59e
2 changed files with 63 additions and 2 deletions
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16
lld/ELF/SyntheticSections.cpp
View File

@@ -922,9 +922,17 @@ template <class ELFT> void MipsGotSection::build() {
continue;
InX::RelaDyn->addReloc(Target->TlsModuleIndexRel, this, Offset, S);
} else {
if (!P.first->IsPreemptible)
// When building a shared library we still need a dynamic relocation
// for the module index. Therefore only checking for
// S->IsPreemptible is not sufficient (this happens e.g. for
// thread-locals that have been marked as local through a linker script)
if (!S->IsPreemptible && !Config->Pic)
continue;
InX::RelaDyn->addReloc(Target->TlsModuleIndexRel, this, Offset, S);
// However, we can skip writing the TLS offset reloc for non-preemptible
// symbols since it is known even in shared libraries
if (!S->IsPreemptible)
continue;
Offset += Config->Wordsize;
InX::RelaDyn->addReloc(Target->TlsOffsetRel, this, Offset, S);
}
@@ -1030,7 +1038,11 @@ void MipsGotSection::writeTo(uint8_t *Buf) {
if (P.first == nullptr && !Config->Pic)
Write(P.second, nullptr, 1);
else if (P.first && !P.first->IsPreemptible) {
Write(P.second, nullptr, 1);
// If we are emitting PIC code with relocations we mustn't write
// anything to the GOT here. When using Elf_Rel relocations the value
// one will be treated as an addend and will cause crashes at runtime
if (!Config->Pic)
Write(P.second, nullptr, 1);
Write(P.second + 1, P.first, -0x8000);
}
}

49
lld/test/ELF/mips-tls-64-pic-local-variable.s Normal file
View File

@@ -0,0 +1,49 @@
# REQUIRES: mips
# MIPS TLS variables that are marked as local by a version script were previously
# writing values to the GOT that caused runtime crashes. This was happending when
# linking jemalloc_tsd.c in FreeBSD libc. Check that we do the right thing now:
# RUN: llvm-mc -filetype=obj -triple=mips64-unknown-freebsd %s -o %t.o
# RUN: echo "{ global: foo; local: *; };" > %t.script
# RUN: ld.lld --version-script %t.script -shared %t.o -o %t.so
# RUN: llvm-objdump --section=.got -s %t.so | FileCheck %s -check-prefix GOT
# RUN: llvm-readobj -r %t.so | FileCheck %s -check-prefix RELOCS
# GOT: Contents of section .got:
# GOT-NEXT: 20000 00000000 00000000 80000000 00000000
# GOT-NEXT: 20010 00000000 00000000 00000000 00000000
# GOT-NEXT: 20020 ffffffff ffff8000
# RELOCS: Section ({{.+}}) .rel.dyn {
# RELOCS-NEXT: 0x20018 R_MIPS_TLS_DTPMOD64/R_MIPS_NONE/R_MIPS_NONE
# RELOCS-NEXT: }
# Test case generated using clang -mcpu=mips4 -target mips64-unknown-freebsd12.0 -fpic -O -G0 -EB -mabi=n64 -msoft-float -std=gnu99 -S %s -o %t.s
# from the following source:
#
# _Thread_local int x;
# int foo() { return x; }
#
.text
.globl foo
.p2align 3
.type foo,@function
.ent foo
foo:
lui $1, %hi(%neg(%gp_rel(foo)))
daddu $1, $1, $25
daddiu $gp, $1, %lo(%neg(%gp_rel(foo)))
ld $25, %call16(__tls_get_addr)($gp)
jalr $25
daddiu $4, $gp, %tlsgd(x)
.end foo
.type x,@object
.section .tbss,"awT",@nobits
.globl x
.p2align 2
x:
.4byte 0
.size x, 4