[llvm-readobj] Display section names for STT_SECTION symbols.

Summary:
This patch will obtain the section name for symbols that refer to a section.  Prior to this patch the Name field for STT_SECTIONs was blank, now it is populated.

Before:
```
Symbol table '.symtab' contains 6 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 0000000000000000     0 SECTION LOCAL  DEFAULT    1
     2: 0000000000000000     0 SECTION LOCAL  DEFAULT    3
     3: 0000000000000000     0 SECTION LOCAL  DEFAULT    4
     4: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND _GLOBAL_OFFSET_TABLE_
     5: 0000000000000000     0 TLS     GLOBAL DEFAULT  UND sym
```

With this patch:
```
Symbol table '.symtab' contains 6 entries:
   Num:    Value          Size Type    Bind   Vis      Ndx Name
     0: 0000000000000000     0 NOTYPE  LOCAL  DEFAULT  UND
     1: 0000000000000000     0 SECTION LOCAL  DEFAULT    1 .text
     2: 0000000000000000     0 SECTION LOCAL  DEFAULT    3 .data
     3: 0000000000000000     0 SECTION LOCAL  DEFAULT    4 .bss
     4: 0000000000000000     0 NOTYPE  GLOBAL DEFAULT  UND _GLOBAL_OFFSET_TABLE_
     5: 0000000000000000     0 TLS     GLOBAL DEFAULT  UND sym
```

This fixes PR40788

Reviewers: jhenderson, rupprecht, espindola

Reviewed By: rupprecht

Subscribers: emaste, javed.absar, arichardson, MaskRay, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D58796

llvm-svn: 355207

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/tools/llvm-readobj/ELFDumper.cpp b/llvm/tools/llvm-readobj/ELFDumper.cpp
index 6428e9926ef..786a028035f 100644
--- a/llvm/tools/llvm-readobj/ELFDumper.cpp
+++ b/llvm/tools/llvm-readobj/ELFDumper.cpp
@@ -814,6 +814,16 @@ std::string ELFDumper<ELFT>::getFullSymbolName(const Elf_Sym *Symbol,
                                                bool IsDynamic) const {
   std::string SymbolName =
       maybeDemangle(unwrapOrError(Symbol->getName(StrTable)));
+
+  if (SymbolName.empty() && Symbol->getType() == ELF::STT_SECTION) {
+    unsigned SectionIndex;
+    StringRef SectionName;
+    Elf_Sym_Range Syms =
+        unwrapOrError(ObjF->getELFFile()->symbols(DotSymtabSec));
+    getSectionNameIndex(Symbol, Syms.begin(), SectionName, SectionIndex);
+    return SectionName;
+  }
+
   if (!IsDynamic)
     return SymbolName;