[llvm-objdump] --syms: print 'u' for STB_GNU_UNIQUE

[MaskRay]

Summary

GCC when configured with --enable-gnu-unique (default on glibc>=2.11)
emits STB_GNU_UNIQUE for certain objects which are otherwise emitted as
STT_OBJECT, such as an inline function's static local variable or its
guard variable, and a static data member of a template.

Clang does not implement -fgnu-unique.

Implementing it as a binding is strange and the feature itself is
considered by some as a misfeature.

[grimar]

LGTM

[jhenderson]

LGTM too.

llvm/test/tools/llvm-objdump/ELF/symbol-table.test

 # CHECK-NEXT:0000000000000000 g       .text 0000000000000000 STT_HIOS
 # CHECK-NEXT:0000000000000000 g       .text 0000000000000000 STT_LOPROC
 # CHECK-NEXT:0000000000000000         *UND* 0000000000000000 undef
 # CHECK-NEXT:0000000000000000         *UND* 0000000000000000 SHN_LOPROC
 # CHECK-NEXT:0000000000000000         *UND* 0000000000000000 SHN_LOOS
 # CHECK-NEXT:0000000000000000         *UND* 0000000000000000 reserve
 # CHECK-NEXT:0000000000000000 g       *ABS* 0000000000000000 abs
 # CHECK-NEXT:0000000000000000         *COM* 0000000000000000 common2
-# CHECK-NEXT:0000000000000000 g     O .data 0000000000000000 gnu_unique
+# CHECK-NEXT:0000000000000000 u     O .data 0000000000000000 gnu_unique
 # CHECK-NEXT:0000000000000000 g       .data 0000000000000000 invalid_binding
 # CHECK-NEXT:0000000000000000 g       .data 0000000000000000 STB_HIOS
 # CHECK-NEXT:0000000000000000 g       .data 0000000000000000 STB_LOPROC
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB

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

for (auto I = O->symbol_begin(), E = O->symbol_end(); I != E; ++I) {
 
     char GlobLoc = ' ';
     if ((Section != O->section_end() || Absolute) && !Weak)
       GlobLoc = Global ? 'g' : 'l';
     char IFunc = ' ';
     if (auto *ELF = dyn_cast<ELFObjectFileBase>(O)) {
       if (ELFSymbolRef(*I).getELFType() == ELF::STT_GNU_IFUNC)
         IFunc = 'i';
+      if (ELFSymbolRef(*I).getBinding() == ELF::STB_GNU_UNIQUE)
+        GlobLoc = 'u';
     }
     char Debug = (Type == SymbolRef::ST_Debug || Type == SymbolRef::ST_File)
                  ? 'd' : ' ';
     char FileFunc = ' ';
     if (Type == SymbolRef::ST_File)
       FileFunc = 'f';
     else if (Type == SymbolRef::ST_Function)
       FileFunc = 'F';