[ELF] - Assign SHF_INFO_LINK flag to REL[A] sections.

[grimar]

Summary

Spec says: (http://www.sco.com/developers/gabi/latest/ch4.sheader.html)

sh_info
This member holds extra information, whose interpretation depends on the section type. A table below describes the values.
If the sh_flags field for this section header includes the attribute SHF_INFO_LINK, then this member represents a section header table index.

SHF_INFO_LINK
The sh_info field of this section header holds a section header table index.

Since sh_info for SHT_REL[A] sections should contain the section header index of the section to which the relocation applies, this is
consistent with spec to put this flag. Behavior matches both bfd and gold as well.

lld/trunk/ELF/OutputSections.cpp

template <class ELFT> void OutputSection::finalize() {
   if (isa<SyntheticSection>(First))
     return;
 
   this->Link = InX::SymTab->getParent()->SectionIndex;
   // sh_info for SHT_REL[A] sections should contain the section header index of
   // the section to which the relocation applies.
   InputSectionBase *S = First->getRelocatedSection();
   Info = S->getOutputSection()->SectionIndex;
+  Flags |= SHF_INFO_LINK;
 }
 
 static uint64_t updateOffset(uint64_t Off, InputSection *S) {
   Off = alignTo(Off, S->Alignment);
   S->OutSecOff = Off;
   return Off + S->getSize();
 }
 

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

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1.o
 # RUN: ld.lld --emit-relocs %t1.o -o %t
-# RUN: llvm-readobj -t -r %t | FileCheck %s
+# RUN: llvm-readobj -t -r -s %t | FileCheck %s
 
 ## Check single dash form.
 # RUN: ld.lld -emit-relocs %t1.o -o %t1
 # RUN: llvm-readobj -t -r %t1 | FileCheck %s
 
 ## Check alias.
 # RUN: ld.lld -q %t1.o -o %t2
 # RUN: llvm-readobj -t -r %t2 | FileCheck %s
 
+# CHECK:      Section {
+# CHECK:        Index: 2
+# CHECK-NEXT:   Name: .rela.text
+# CHECK-NEXT:   Type: SHT_RELA
+# CHECK-NEXT:   Flags [
+# CHECK-NEXT:     SHF_INFO_LINK
+# CHECK-NEXT:   ]
 # CHECK:      Relocations [
 # CHECK-NEXT:   Section ({{.*}}) .rela.text {
 # CHECK-NEXT:     0x201002 R_X86_64_32 .text 0x1
 # CHECK-NEXT:     0x201007 R_X86_64_PLT32 fn 0xFFFFFFFFFFFFFFFC
 # CHECK-NEXT:     0x20100E R_X86_64_32 .text 0xD
 # CHECK-NEXT:     0x201013 R_X86_64_PLT32 fn2 0xFFFFFFFFFFFFFFFC
 # CHECK-NEXT:   }
 # CHECK-NEXT: ]