[yaml2obj] - Allow specifying custom Link values for SHT_HASH section.

[grimar]

Summary

This allows setting any sh_link values for SHT_HASH sections.

Depends on D68085.

[jhenderson]

LGTM, with one suggestion.

test/tools/yaml2obj/elf-hash-section.yaml

154–160

The spacing here isn't lined up like it is in the other ones above. I think it should be something like:

# LINK:      Name: .hash1
# LINK:      Link:
# LINK-SAME:       123

# LINK:      Name: .hash2
# LINK:      Link:
# LINK-SAME:       1

lib/ObjectYAML/ELFEmitter.cpp

 template <class ELFT>
 void ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                          const ELFYAML::HashSection &Section,
                                          ContiguousBlobAccumulator &CBA) {
   raw_ostream &OS =
       CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
 
   unsigned Link = 0;
-  if (SN2I.lookup(".dynsym", Link))
+  if (Section.Link.empty() && SN2I.lookup(".dynsym", Link))
     SHeader.sh_link = Link;
 
   if (Section.Content) {
     SHeader.sh_size = writeContent(OS, Section.Content, None);
     return;
   }
 
   support::endian::write<uint32_t>(OS, Section.Bucket->size(),

test/tools/yaml2obj/elf-hash-section.yaml

 FileHeader:
   Class:   ELFCLASS32
   Data:    ELFDATA2LSB
   Type:    ET_DYN
   Machine: EM_386
 Sections:
   - Name:  .hash
     Type:  SHT_HASH
+
+## Check we can set any sh_link value with use of the "Link" tag.
+
+# RUN: yaml2obj --docnum=8 %s -o %t8
+# RUN: llvm-readobj --sections %t8 | FileCheck %s --check-prefix=LINK
+
+# LINK: Name: .hash1
+# LINK: Link:
+# LINK-SAME: 123
+
+# LINK: Name: .hash2
+# LINK: Link:
+# LINK-SAME: 1
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS32
+  Data:    ELFDATA2LSB
+  Type:    ET_DYN
+  Machine: EM_386
+Sections:
+  - Name: .hash1
+    Type: SHT_HASH
+    Content: ""
+    Link: 123
+  - Name: .hash2
+    Type: SHT_HASH
+    Content: ""
+    Link: .hash1
+## SHT_HASH is linked to dynamic symbol table by default if it exists.
+  - Name: .dynsym
+    Type: SHT_DYNSYM