[ELF] Use the Repl point to avoid the segfault when using ICF

[phosek]

Summary

This addresses PR38918.

[phosek]

I haven't managed to come up with a minimal reproducer yet, but this addresses the issue when using the reproducer attached in https://bugs.llvm.org/show_bug.cgi?id=38918.

[phosek]

Now also includes a reproducer.

[phosek]

So after looking a bit more into the output of the reproducer, I realized this is not the correct solution because it leads to relocations being duplicated. Instead, relocations for the folded section shouldn't be emitted at all so this's a deeper rooted issue.

[mcgrathr]

The test will need to verify that the emitted relocs are correct too.

[ruiu]

lld/test/ELF/icf18.s

1 ↗

(On Diff #165891)

This is not an assembly although the file extension is .s. Can you write this in assembly?

[ruiu]

LGTM

lld/ELF/InputSection.cpp

if (Sym.Type == STT_SECTION) {
         // not calculate relocations in this mode and loses
         // individual "gp" values used by each input object file.
         // As a workaround we add the "gp" value to the relocation
         // addend and save it back to the file.
         Addend += Sec->getFile<ELFT>()->MipsGp0;
       }
 
       if (RelTy::IsRela)
-        P->r_addend = Sym.getVA(Addend) - Section->getOutputSection()->Addr;
+        P->r_addend = Sym.getVA(Addend) - Section->Repl->getOutputSection()->Addr;
       else if (Config->Relocatable)
         Sec->Relocations.push_back({R_ABS, Type, Rel.r_offset, Addend, &Sym});
     }
   }
 }
 
 // The ARM and AArch64 ABI handle pc-relative relocations to undefined weak
 // references specially. The general rule is that the value of the symbol in

lld/test/ELF/emit-relocs-icf1.s

+# REQUIRES: x86
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t.o
+# RUN: ld.lld --emit-relocs --icf=all %t.o -o %t
+# RUN: llvm-readobj -r %t | FileCheck %s
+
+# CHECK:      Relocations [
+# CHECK-NEXT:   Section (2) .rela.text {
+# CHECK-NEXT:     0x201000 R_X86_64_64 .text 0x11
+# CHECK-NEXT:   }
+# CHECK-NEXT: ]
+
+.section .text.foo,"ax"
+
+.section .text.bar,"ax"
+
+.text
+relocs:
+.quad .text.foo
+.quad .text.bar
+
+.global _start
+_start:
+  nop