[yaml2elf/obj2yaml] - Allow normal parsing/dumping of the .rela.dyn s…

…ection

.rela.dyn is a section that has sh_info normally
set to zero. And Info is an optional field in the description
of the relocation section in YAML.

But currently, yaml2obj would fail to produce the object when
Info is not explicitly listed.

The patch fixes the issue.

Differential revision: https://reviews.llvm.org/D60820

llvm-svn: 358656

llvm/test/tools/obj2yaml/elf-reladyn-section-shinfo.yaml

@@ -0,0 +1,44 @@
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-readobj --sections %t | FileCheck %s
+# RUN: obj2yaml %t | FileCheck %s --check-prefix=YAML
+
+## .rela.dyn is a dynamic relocation section that normally has
+## no value in sh_info field. Check we are able to use
+## yaml2obj/obj2yaml without needing to explicitly set it.
+
+# CHECK:      Name: .rela.dyn
+# CHECK-NEXT: Type: SHT_RELA
+# CHECK-NEXT: Flags [
+# CHECK-NEXT:   SHF_ALLOC
+# CHECK-NEXT: ]
+# CHECK-NEXT: Address:
+# CHECK-NEXT: Offset:
+# CHECK-NEXT: Size:
+# CHECK-NEXT: Link:
+# CHECK-NEXT: Info: 0
+# CHECK-NEXT: AddressAlignment:
+# CHECK-NEXT: EntrySize:
+
+# YAML:      - Name:    .rela.dyn
+# YAML-NEXT:   Type:    SHT_RELA
+# YAML-NEXT:   Flags:   [ SHF_ALLOC ]
+# YAML-NEXT:   Link:    .dynsym
+# YAML-NEXT:   EntSize: 0x0000000000000018
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_X86_64
+  Entry:   0x0000000000001000
+Sections:
+  - Name:    .rela.dyn
+    Type:    SHT_RELA
+    Flags:   [ SHF_ALLOC ]
+    Link:    .dynsym
+    EntSize: 0x0000000000000018
+# Add at least one symbol to trigger the .dynsym emission.
+DynamicSymbols:
+  - Name:    bar
+    Binding: STB_GLOBAL

llvm/tools/yaml2obj/yaml2elf.cpp

@@ -278,8 +278,9 @@ bool ELFState<ELFT>::initSectionHeaders(std::vector<Elf_Shdr> &SHeaders,
         // For relocation section set link to .symtab by default.
         SHeader.sh_link = getDotSymTabSecNo();
 
-      unsigned Index;
-      if (!convertSectionIndex(SN2I, S->Name, S->RelocatableSec, Index))
+      unsigned Index = 0;
+      if (!S->RelocatableSec.empty() &&
+          !convertSectionIndex(SN2I, S->Name, S->RelocatableSec, Index))
         return false;
       SHeader.sh_info = Index;
       if (!writeSectionContent(SHeader, *S, CBA))