[ELF] -r: fix R_*_NONE to section symbols on Elf*_Rel targets

[MaskRay]

Summary

On Elf*_Rel targets, for a relocation to a section symbol, an R_ABS is
added to compute the implicit addend which will be applied in the
relocated location.

Addends of R_*_NONE should be ignored, so don't emit an R_ABS.

This fixes crashes on X86 and ARM (their relocateOne() do not handle
R_*_NONE).

[peter.smith]

LGTM. The addend in a R_*_NONE relocation is not meaningful anyway as the relocation is never resolved to a value.

[MaskRay]

Update description

[MaskRay]

This comment was removed by MaskRay.

ELF/InputSection.cpp

if (Sym.Type == STT_SECTION) {
         // 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;
-      else if (Config->Relocatable)
+      else if (Config->Relocatable && Type != Target->NoneRel)
         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
 // this context is the address of the place P. A further special case is that

test/ELF/relocation-none-arm.s

 # RUN: llvm-mc -filetype=obj -triple=armv7-linux-musl %s -o %t.o
 # RUN: ld.lld --gc-sections %t.o -o %t
 # RUN: llvm-readelf -S -r %t | FileCheck %s
 
 # Test that we discard R_ARM_NONE, but respect the references it creates among
 # sections.
 
 # CHECK: .data
 # CHECK: There are no relocations in this file.
 
+# RUN: ld.lld -r %t.o -o %t
+# RUN: llvm-readobj -r %t | FileCheck --check-prefix=RELOC %s
+
+# RELOC:      Section ({{.*}}) .rel.text {
+# RELOC-NEXT:   0x0 R_ARM_NONE .data 0x0
+# RELOC-NEXT: }
+
 .globl _start
 _start:
   nop
   .reloc 0, R_ARM_NONE, .data
 
 .data
   .long 0

test/ELF/relocation-none-i386.s

 # RUN: llvm-mc -filetype=obj -triple=i386-linux-musl %s -o %t.o
 # RUN: ld.lld --gc-sections %t.o -o %t
 # RUN: llvm-readelf -S -r %t | FileCheck %s
 
 # Test that we discard R_386_NONE, but respect the
 # references it creates among sections.
 
 # CHECK: .data
 # CHECK: There are no relocations in this file.
 
+# RUN: ld.lld -r %t.o -o %t
+# RUN: llvm-readobj -r %t | FileCheck --check-prefix=RELOC %s
+
+# RELOC:      Section ({{.*}}) .rel.text {
+# RELOC-NEXT:   0x0 R_386_NONE .data 0x0
+# RELOC-NEXT: }
+
 .globl _start
 _start:
   ret
   .reloc 0, R_386_NONE, .data
 
 .data
   .long 0