[llvm-readelf] - Do no print an empty symbol version as "<corrupt>"

[grimar]

Summary

It is discussed here https://reviews.llvm.org/D71118#inline-643172

Currently when a version is empty, llvm-readelf prints:
"000: 0 (*local*) 2 (<corrupt>)"

But GNU readelf does not treat empty section as corrupt.
There is no sense in having empty versions anyways it seems, but
this change is for consistency with GNU.

[jhenderson]

LGTM. Might want to wait for others to have a chance to comment too.

[MaskRay]

I think linkers (GNU ld, gold, and lld) don't create empty version names (vda_name). I don't mind whether this is <corrupt> or empty.

llvm/test/tools/llvm-readobj/ELF/verneed-invalid.test

 ## Test how llvm-readobj/llvm-readelf tools handle invalid SHT_GNU_verneed sections.
 
 ## In the first case we have a SHT_GNU_versym section that refers to
 ## a version listed in a SHT_GNU_verneed section. That version has an
 ## empty name, making it invalid.
 
 # RUN: yaml2obj --docnum=1 %s -o %t1
 # RUN: llvm-readelf -V %t1 | FileCheck %s --check-prefix=GNU-VERNEED-NAME
 # RUN: llvm-readobj -V %t1 | FileCheck %s --check-prefix=LLVM-VERNEED-NAME
 
 # GNU-VERNEED-NAME:      Version symbols section '.gnu.version' contains 2 entries:
 # GNU-VERNEED-NAME-NEXT:  Addr: 0000000000200210  Offset: 0x000040  Link: 5 (.dynsym)
-# GNU-VERNEED-NAME-NEXT:   000:   0 (*local*)       2 (<corrupt>)
+# GNU-VERNEED-NAME-NEXT:   000:   0 (*local*)       2 ()
 
 # GNU-VERNEED-NAME:      Version needs section '.gnu.version_r' contains 1 entries:
 # GNU-VERNEED-NAME-NEXT:  Addr: 0000000000000000  Offset: 0x000044  Link: 6 (.dynstr)
 # GNU-VERNEED-NAME-NEXT:   0x0000: Version: 1  File: somefile  Cnt: 1
 # GNU-VERNEED-NAME-NEXT:   0x0010:   Name:   Flags: none  Version: 2
 
 # LLVM-VERNEED-NAME:      VersionSymbols [
 # LLVM-VERNEED-NAME:        Symbol {

llvm/tools/llvm-readobj/ELFDumper.cpp

for (size_t I = 0, E = VerTable.size(); I < E; ++I) {
     if (Ndx == VER_NDX_LOCAL || Ndx == VER_NDX_GLOBAL) {
       Versions.emplace_back(Ndx == VER_NDX_LOCAL ? "*local*" : "*global*");
       continue;
     }
 
     bool IsDefault;
     Expected<StringRef> NameOrErr =
         this->dumper()->getSymbolVersionByIndex(Ndx, IsDefault);
-    if (!NameOrErr || NameOrErr->empty()) {
+    if (!NameOrErr) {
       if (!NameOrErr) {
         unsigned SecNdx = Sec - &cantFail(Obj->sections()).front();
         this->reportUniqueWarning(createError(
             "unable to get a version for entry " + Twine(I) +
             " of SHT_GNU_versym section with index " + Twine(SecNdx) + ": " +
             toString(NameOrErr.takeError())));
       }
       Versions.emplace_back("<corrupt>");