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[ELF] -z notext: avoid dynamic relocations in .eh_frame

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Fix https://github.com/llvm/llvm-project/issues/60392

```
// a.cc
void raise() { throw 42; }
bool foo() {
  try { raise(); } catch (int) { return true; }
  return false;
}
int main() { foo(); }
```

```
clang++ --target=x86_64-linux-gnu -fno-pic -mcmodel=large -no-pie -fuse-ld=lld -z notext a.cc -o a && ./a
clang++ --target=aarch64-linux-gnu -fno-pic -no-pie -fuse-ld=lld -Wl,--dynamic-linker=/usr/aarch64-linux-gnu/lib/ld-linux-aarch64.so.1 -Wl,-rpath=/usr/aarch64-linux-gnu/lib -z notext a.cc -o a && ./a
```
Both commands fail because we produce a dynamic relocation for
R_X86_64_64/R_AARCH64_ABS64 in .eh_frame which will be adjusted to a wrong
offset by `SectionBase::getOffset` after D122459.

Since GNU ld uses a canonical PLT entry instead of a dynamic relocation for
.eh_frame, we follow suit as well to avoid the issue.

Mips has an ABI issue (https://github.com/llvm/llvm-project/issues/5837) and we
don't implement GNU ld's DW_EH_PE_absptr conversion. mips64-eh-abs-reloc.s wants
a dynamic relocation, so keep the original behavior for EM_MIPS.

Differential Revision: https://reviews.llvm.org/D143136
This commit is contained in:
Fangrui Song
2023-02-03 10:27:33 -08:00
parent 98f0e4f611
commit 08c915fa76
2 changed files with 39 additions and 1 deletions
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10
lld/ELF/Relocations.cpp
View File

@@ -1079,7 +1079,15 @@ void RelocationScanner::processAux(RelExpr expr, RelType type, uint64_t offset,
return;
}
bool canWrite = (sec->flags & SHF_WRITE) || !config->zText;
// Use a simple -z notext rule that treats all sections except .eh_frame as
// writable. GNU ld does not produce dynamic relocations in .eh_frame (and our
// SectionBase::getOffset would incorrectly adjust the offset).
//
// For MIPS, we don't implement GNU ld's DW_EH_PE_absptr to DW_EH_PE_pcrel
// conversion. We still emit a dynamic relocation.
bool canWrite = (sec->flags & SHF_WRITE) ||
!(config->zText ||
(isa<EhInputSection>(sec) && config->emachine != EM_MIPS));
if (canWrite) {
RelType rel = target->getDynRel(type);
if (expr == R_GOT || (rel == target->symbolicRel && !sym.isPreemptible)) {

30
lld/test/ELF/eh-frame-znotext.s Normal file
View File

@@ -0,0 +1,30 @@
# REQUIRES: aarch64
## While a symbolic relocation for -z notext in .eh_frame can emit a dynamic
## relocation, we try avoiding that (https://github.com/llvm/llvm-project/issues/60392)
## and use a canonical PLT entry instead.
# RUN: rm -rf %t && split-file %s %t && cd %t
# RUN: llvm-mc -filetype=obj -triple=aarch64 a.s -o a.o
# RUN: llvm-mc -filetype=obj -triple=aarch64 abi.s -o abi.o
# RUN: ld.lld -shared abi.o -o abi.so
# RUN: ld.lld a.o abi.so -o a
# RUN: llvm-readelf -r --dyn-syms a | FileCheck %s
# RUN: ld.lld -z notext a.o abi.so -o a
# RUN: llvm-readelf -r --dyn-syms a | FileCheck %s
# CHECK: R_AARCH64_JUMP_SLOT {{.*}} __gxx_personality_v0 + 0
# CHECK: 1: 00000000002{{.*}} 0 FUNC GLOBAL DEFAULT UND __gxx_personality_v0
#--- a.s
foo:
.cfi_startproc
.cfi_personality 0, __gxx_personality_v0
ret
.cfi_endproc
#--- abi.s
.globl __gxx_personality_v0
.type __gxx_personality_v0, @function
__gxx_personality_v0: