[yaml2obj/obj2yaml] - Add support for SHT_LLVM_DEPENDENT_LIBRARIES sections.

This section contains strings specifying libraries to be added to the link by the linker.
The strings are encoded as standard null-terminated UTF-8 strings.

This patch adds a way to describe and dump SHT_LLVM_DEPENDENT_LIBRARIES sections.

I introduced a new YAMLFlowString type here. That used to teach obj2yaml to dump
them like:

```
Libraries: [ foo, bar ]
```

instead of the following (if StringRef would be used):

```
Libraries:
  - foo
  - bar
```

Differential revision: https://reviews.llvm.org/D70598

1 files changed, 37 insertions, 0 deletions

diff --git a/llvm/tools/obj2yaml/elf2yaml.cpp b/llvm/tools/obj2yaml/elf2yaml.cpp
index 15c38c630b9..3dc48b8b880 100644
--- a/llvm/tools/obj2yaml/elf2yaml.cpp
+++ b/llvm/tools/obj2yaml/elf2yaml.cpp
@@ -62,6 +62,8 @@ class ELFDumper {
   Expected<ELFYAML::AddrsigSection *> dumpAddrsigSection(const Elf_Shdr *Shdr);
   Expected<ELFYAML::LinkerOptionsSection *>
   dumpLinkerOptionsSection(const Elf_Shdr *Shdr);
+  Expected<ELFYAML::DependentLibrariesSection *>
+  dumpDependentLibrariesSection(const Elf_Shdr *Shdr);
   Expected<ELFYAML::DynamicSection *> dumpDynamicSection(const Elf_Shdr *Shdr);
   Expected<ELFYAML::RelocationSection *> dumpRelocSection(const Elf_Shdr *Shdr);
   Expected<ELFYAML::RawContentSection *>
@@ -325,6 +327,14 @@ template <class ELFT> Expected<ELFYAML::Object *> ELFDumper<ELFT>::dump() {
       Y->Chunks.emplace_back(*SecOrErr);
       break;
     }
+    case ELF::SHT_LLVM_DEPENDENT_LIBRARIES: {
+      Expected<ELFYAML::DependentLibrariesSection *> SecOrErr =
+          dumpDependentLibrariesSection(&Sec);
+      if (!SecOrErr)
+        return SecOrErr.takeError();
+      Y->Chunks.emplace_back(*SecOrErr);
+      break;
+    }
     case ELF::SHT_NULL: {
       // We only dump the SHT_NULL section at index 0 when it
       // has at least one non-null field, because yaml2obj
@@ -630,6 +640,33 @@ ELFDumper<ELFT>::dumpLinkerOptionsSection(const Elf_Shdr *Shdr) {
 }
 
 template <class ELFT>
+Expected<ELFYAML::DependentLibrariesSection *>
+ELFDumper<ELFT>::dumpDependentLibrariesSection(const Elf_Shdr *Shdr) {
+  auto DL = std::make_unique<ELFYAML::DependentLibrariesSection>();
+  if (Error E = dumpCommonSection(Shdr, *DL))
+    return std::move(E);
+
+  Expected<ArrayRef<uint8_t>> ContentOrErr = Obj.getSectionContents(Shdr);
+  if (!ContentOrErr)
+    return ContentOrErr.takeError();
+
+  ArrayRef<uint8_t> Content = *ContentOrErr;
+  if (!Content.empty() && Content.back() != 0) {
+    DL->Content = Content;
+    return DL.release();
+  }
+
+  DL->Libs.emplace();
+  for (const uint8_t *I = Content.begin(), *E = Content.end(); I < E;) {
+    StringRef Lib((const char *)I);
+    DL->Libs->emplace_back(Lib);
+    I += Lib.size() + 1;
+  }
+
+  return DL.release();
+}
+
+template <class ELFT>
 Expected<ELFYAML::DynamicSection *>
 ELFDumper<ELFT>::dumpDynamicSection(const Elf_Shdr *Shdr) {
   auto S = std::make_unique<ELFYAML::DynamicSection>();