Commit 56d81104 authored by Fangrui Song's avatar Fangrui Song
Browse files

[ELF] -r: fix crash when processing a SHT_REL[A] that relocates a SHF_MERGE after D67504/r372734 

Fix PR43767

In -r mode, when processing a SHT_REL[A] that relocates a SHF_MERGE, sec->getRelocatedSection() is a
MergeInputSection and its parent is an OutputSection but is asserted to
be a SyntheticSection (MergeSyntheticSection) in LinkerScript.cpp:addInputSec().
 ##
The code path is not exercised in non -r mode because the relocated
section changed from MergeInputSection to InputSection.

Reorder the code to make the non -r logic apply to -r as well, thus fix
the crash.

Reviewed By: peter.smith

Differential Revision: https://reviews.llvm.org/D69364
parent 267cc329

lld/ELF/InputFiles.cpp

+10 −10
Original line number Diff line number Diff line
@@ -838,6 +838,16 @@ InputSectionBase *ObjFile<ELFT>::createInputSection(const Elf_Shdr &sec) { 
    if (!target)

      return nullptr;



    // ELF spec allows mergeable sections with relocations, but they are

    // rare, and it is in practice hard to merge such sections by contents,

    // because applying relocations at end of linking changes section

    // contents. So, we simply handle such sections as non-mergeable ones.

    // Degrading like this is acceptable because section merging is optional.

    if (auto *ms = dyn_cast<MergeInputSection>(target)) {

      target = toRegularSection(ms);

      this->sections[sec.sh_info] = target;

    }



    // This section contains relocation information.

    // If -r is given, we do not interpret or apply relocation

    // but just copy relocation sections to output.
@@ -856,16 +866,6 @@ InputSectionBase *ObjFile<ELFT>::createInputSection(const Elf_Shdr &sec) { 
      fatal(toString(this) +

            ": multiple relocation sections to one section are not supported");



    // ELF spec allows mergeable sections with relocations, but they are

    // rare, and it is in practice hard to merge such sections by contents,

    // because applying relocations at end of linking changes section

    // contents. So, we simply handle such sections as non-mergeable ones.

    // Degrading like this is acceptable because section merging is optional.

    if (auto *ms = dyn_cast<MergeInputSection>(target)) {

      target = toRegularSection(ms);

      this->sections[sec.sh_info] = target;

    }



    if (sec.sh_type == SHT_RELA) {

      ArrayRef<Elf_Rela> rels = CHECK(getObj().relas(&sec), this);

      target->firstRelocation = rels.begin();

lld/test/ELF/merge-relocatable.s

0 → 100644
+23 −0
Original line number Diff line number Diff line 
# REQUIRES: x86



## Test that we keep a SHT_REL[A] section which relocates a SHF_MERGE section

## in -r mode. The relocated SHF_MERGE section is handled as non-mergeable.



# RUN: llvm-mc -filetype=obj -triple=x86_64 %s -o %t.o

# RUN: ld.lld -r %t.o -o %t

# RUN: llvm-readobj -S %t | FileCheck %s



# CHECK:     Name: .rodata.cst8

# CHECK-NOT: }

# CHECK:     Size: 16

# CHECK:     Name: .rela.rodata.cst8

# CHECK-NOT: }

# CHECK:     Size: 48



foo:



.section .rodata.cst8,"aM",@progbits,8,unique,0

.quad foo



.section .rodata.cst8,"aM",@progbits,8,unique,1

.quad foo