[ELF] - Do not crash with --emit-relocs and --icf=all together.

[grimar]

Summary

Previously we would crash because did not mark .rel[a] sections
as dead and they tried to access parent which was not live
after ICF and therefore was null.

[ruiu]

replace is not designed to be smart, and adding new code there seems semantically incorrect, as replacing some section doesn't necessarily mean that its dependent sections should be marked as dead.

You could instead add code to ICF.cpp.

[grimar]

• Addressed comments.

[grimar]

In D43241#1006538, @ruiu wrote:

replace is not designed to be smart, and adding new code there seems semantically incorrect, as replacing some section doesn't necessarily mean that its dependent sections should be marked as dead.

You could instead add code to ICF.cpp.

Thanks, with that I was able to simplify code a bit more.

lld/trunk/ELF/InputSection.cpp

template <class ELFT> void InputSection::writeTo(uint8_t *Buf) {
   uint8_t *BufEnd = Buf + OutSecOff + Data.size();
   relocate<ELFT>(Buf, BufEnd);
 }
 
 void InputSection::replace(InputSection *Other) {
   Alignment = std::max(Alignment, Other->Alignment);
   Other->Repl = Repl;
   Other->Live = false;
+  for (InputSection *IS : Other->DependentSections)
+    IS->Live = false;
 }
 
 template <class ELFT>
 EhInputSection::EhInputSection(ObjFile<ELFT> &F,
                                const typename ELFT::Shdr &Header,
                                StringRef Name)
     : InputSectionBase(F, Header, Name, InputSectionBase::EHFrame) {}
 

lld/trunk/test/ELF/emit-relocs-icf.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1.o
+# RUN: ld.lld --emit-relocs --icf=all %t1.o -o %t
+# RUN: llvm-readobj -r %t | FileCheck %s
+
+# CHECK:      Relocations [
+# CHECK-NEXT:   Section {{.*}} .rela.text {
+# CHECK-NEXT:     R_X86_64_32 .text 0x1
+# CHECK-NEXT:     R_X86_64_PLT32 fn 0xFFFFFFFFFFFFFFFC
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+
+.section .text.fn,"ax",@progbits,unique,0
+.globl fn
+.type fn,@function
+fn:
+ nop
+
+bar:
+  movl $bar, %edx
+  callq fn@PLT
+  nop
+
+.section .text.fn2,"ax",@progbits,unique,1
+.globl fn2
+.type fn2,@function
+fn2:
+ nop
+
+foo:
+  movl $foo, %edx
+  callq fn2@PLT
+  nop