[ELF] - Set sh_info and sh_link for .rela.plt sections.

This is https://bugs.llvm.org/show_bug.cgi?id=37538,

Currently, LLD may set both sh_link and sh_info for
.rela.plt section to zero when we have only .rela.iplt section part used.

ELF spec (https://docs.oracle.com/cd/E19683-01/816-1386/chapter6-94076/index.html)
says that for SHT_REL and SHT_RELA, sh_link references the associated symbol table
and sh_info the "section to which the relocation applies."

When we set the sh_link field, for the regular case we use the .dynsym index.
For .rela.iplt sections, it is unclear what is the associated symbol table,
because R_*_RELATIVE relocations do not use symbol names and we might have no
.dynsym section at all so this patch uses .symtab section index.

Differential revision: https://reviews.llvm.org/D52830

llvm-svn: 344226

lld/ELF/SyntheticSections.cpp

@@ -1493,9 +1493,12 @@ void RelocationBaseSection::addReloc(const DynamicReloc &Reloc) {
 void RelocationBaseSection::finalizeContents() {
   // If all relocations are R_*_RELATIVE they don't refer to any
   // dynamic symbol and we don't need a dynamic symbol table. If that
-  // is the case, just use 0 as the link.
-  getParent()->Link =
-      In.DynSymTab ? In.DynSymTab->getParent()->SectionIndex : 0;
+  // is the case, just use the index of the regular symbol table section.
+  getParent()->Link = In.DynSymTab ? In.DynSymTab->getParent()->SectionIndex
+                                   : In.SymTab->getParent()->SectionIndex;
+
+  if (In.RelaIplt == this || In.RelaPlt == this)
+    getParent()->Info = In.GotPlt->getParent()->SectionIndex;
 }
 
 RelrBaseSection::RelrBaseSection()

lld/test/ELF/aarch64-gnu-ifunc.s

@@ -15,8 +15,8 @@
 // CHECK-NEXT:  Address: [[RELA:.*]]
 // CHECK-NEXT:  Offset: 0x158
 // CHECK-NEXT:  Size: 48
-// CHECK-NEXT:  Link: 0
-// CHECK-NEXT:  Info: 0
+// CHECK-NEXT:  Link: 6
+// CHECK-NEXT:  Info: 4
 // CHECK-NEXT:  AddressAlignment: 8
 // CHECK-NEXT:  EntrySize: 24
 // CHECK-NEXT: }

lld/test/ELF/dynamic-reloc.s

@@ -18,7 +18,7 @@
 // CHECK-NEXT: Offset:
 // CHECK-NEXT: Size: [[RELASIZE:.*]]
 // CHECK-NEXT: Link: 1
-// CHECK-NEXT: Info: 0
+// CHECK-NEXT: Info: 7
 // CHECK-NEXT: AddressAlignment: 8
 // CHECK-NEXT: EntrySize: 24
 

lld/test/ELF/gnu-ifunc-i386.s

@@ -15,8 +15,8 @@
 // CHECK-NEXT:  Address: [[RELA:.*]]
 // CHECK-NEXT:  Offset: 0xD4
 // CHECK-NEXT:  Size: 16
-// CHECK-NEXT:  Link: 0
-// CHECK-NEXT:  Info: 0
+// CHECK-NEXT:  Link: 6
+// CHECK-NEXT:  Info: 4
 // CHECK-NEXT:  AddressAlignment: 4
 // CHECK-NEXT:  EntrySize: 8
 // CHECK-NEXT: }

lld/test/ELF/gnu-ifunc.s

@@ -15,11 +15,16 @@
 // CHECK-NEXT:  Address: [[RELA:.*]]
 // CHECK-NEXT:  Offset: 0x158
 // CHECK-NEXT:  Size: 48
-// CHECK-NEXT:  Link: 0
-// CHECK-NEXT:  Info: 0
+// CHECK-NEXT:  Link: [[SYMTAB:.*]]
+// CHECK-NEXT:  Info: [[GOTPLT:.*]]
 // CHECK-NEXT:  AddressAlignment: 8
 // CHECK-NEXT:  EntrySize: 24
 // CHECK-NEXT: }
+// CHECK:      Index: [[GOTPLT]]
+// CHECK-NEXT: Name: .got.plt
+// CHECK:      Index: [[SYMTAB]]
+// CHECK-NEXT: Name: .symtab
+// CHECK-NEXT: Type: SHT_SYMTAB
 // CHECK:      Relocations [
 // CHECK-NEXT:   Section ({{.*}}) .rela.plt {
 // CHECK-NEXT:     0x202000 R_X86_64_IRELATIVE