[ELF] Return the section name when calling getSymbolName on a section…

… symbol.

Summary:
Previously, llvm-nm would report symbols for .debug and .note sections as: '?' with an empty  section name:

```
00000000 ?
00000000 ?
...
```

With this patch the output more closely resembles GNU nm:
```
00000000 N .debug_abbrev
00000000 n .note.GNU-stack
...
```

This patch calls `getSectionName` for sections that belong to symbols of type `ELF::STT_SECTION`, which returns the name of the section from the section string table.

Reviewers: Bigcheese, davide, jhenderson

Reviewed By: davide, jhenderson

Subscribers: rupprecht, jhenderson, llvm-commits

Differential Revision: https://reviews.llvm.org/D57105

llvm-svn: 352785

llvm/include/llvm/Object/ELFObjectFile.h

@@ -440,7 +440,16 @@ Expected<StringRef> ELFObjectFile<ELFT>::getSymbolName(DataRefImpl Sym) const {
   auto SymStrTabOrErr = EF.getStringTable(StringTableSec);
   if (!SymStrTabOrErr)
     return SymStrTabOrErr.takeError();
-  return ESym->getName(*SymStrTabOrErr);
+  Expected<StringRef> Name = ESym->getName(*SymStrTabOrErr);
+
+  // If the symbol name is empty use the section name.
+  if ((!Name || Name->empty()) && ESym->getType() == ELF::STT_SECTION) {
+    StringRef SecName;
+    Expected<section_iterator> Sec = getSymbolSection(Sym);
+    if (Sec && !(*Sec)->getName(SecName))
+      return SecName;
+  }
+  return Name;
 }
 
 template <class ELFT>

llvm/test/Object/nm-trivial-object.test

@@ -18,6 +18,8 @@ RUN: llvm-nm %p/Inputs/weak.elf-x86-64 \
 RUN:         | FileCheck %s -check-prefix WEAK-ELF64
 RUN: llvm-nm %p/Inputs/absolute.elf-x86-64 \
 RUN:         | FileCheck %s -check-prefix ABSOLUTE-ELF64
+RUN: llvm-nm -a %p/Inputs/IsNAN.o \
+RUN:         | FileCheck %s -check-prefix ELF64-DEBUG-SYMS
 RUN: llvm-nm %p/Inputs/trivial-object-test.macho-i386 \
 RUN:         | FileCheck %s -check-prefix macho
 RUN: llvm-nm -U %p/Inputs/trivial-object-test.macho-i386 \
@@ -113,6 +115,22 @@ WEAK-ELF64: 0000000000000000 V x2
 ABSOLUTE-ELF64: 0000000000000123 a a1
 ABSOLUTE-ELF64: 0000000000000123 A a2
 
+ELF64-DEBUG-SYMS: 00000000 b .bss
+ELF64-DEBUG-SYMS: 00000000 d .data
+ELF64-DEBUG-SYMS: 00000000 N .debug_abbrev
+ELF64-DEBUG-SYMS: 00000000 N .debug_aranges
+ELF64-DEBUG-SYMS: 00000000 N .debug_frame
+ELF64-DEBUG-SYMS: 00000000 N .debug_info
+ELF64-DEBUG-SYMS: 00000000 N .debug_line
+ELF64-DEBUG-SYMS: 00000000 N .debug_pubnames
+ELF64-DEBUG-SYMS: 00000000 n .note.GNU-stack
+ELF64-DEBUG-SYMS: 00000000 t .text
+ELF64-DEBUG-SYMS: 00000000 a IsNAN.cpp
+ELF64-DEBUG-SYMS: 00000014 T _ZN4llvm5IsNANEd
+ELF64-DEBUG-SYMS: 00000000 T _ZN4llvm5IsNANEf
+ELF64-DEBUG-SYMS:          U __isnan
+ELF64-DEBUG-SYMS:          U __isnanf
+
 macho:          U _SomeOtherFunction
 macho: 00000000 T _main
 macho:          U _puts

llvm/tools/llvm-objdump/llvm-objdump.cpp

@@ -941,8 +941,11 @@ static void disassembleObject(const Target *TheTarget, const ObjectFile *Obj,
       report_error(Obj->getFileName(), SectionOrErr.takeError());
 
     uint8_t SymbolType = ELF::STT_NOTYPE;
-    if (Obj->isELF())
+    if (Obj->isELF()) {
       SymbolType = getElfSymbolType(Obj, Symbol);
+      if (SymbolType == ELF::STT_SECTION)
+        continue;
+    }
 
     section_iterator SecI = *SectionOrErr;
     if (SecI != Obj->section_end())