[llvm-objdump] Change symbol name/PLT decoding errors to warnings

If the referenced symbol of a J[U]MP_SLOT is invalid (e.g. symbol index 0), llvm-objdump -d will bail out:

```
error: 'a': st_name (0x326600) is past the end of the string table of size 0x7
```

where 0x326600 is the st_name field of the first entry past the end of .symtab

Change it to a warning to continue dumping.
`X86/plt.test` uses a prebuilt executable, so I pick `ELF/AArch64/plt.test`
which has a YAML input and can be easily modified.

Reviewed By: jhenderson

Differential Revision: https://reviews.llvm.org/D85623

1 files changed, 3 insertions, 1 deletions

diff --git a/llvm/tools/llvm-cfi-verify/lib/FileAnalysis.cpp b/llvm/tools/llvm-cfi-verify/lib/FileAnalysis.cpp
index d2b4db3b5..1070446 100644
--- a/llvm/tools/llvm-cfi-verify/lib/FileAnalysis.cpp
+++ b/llvm/tools/llvm-cfi-verify/lib/FileAnalysis.cpp
@@ -568,7 +568,9 @@ Error FileAnalysis::parseSymbolTable() {
   }
   if (auto *ElfObject = dyn_cast<object::ELFObjectFileBase>(Object)) {
     for (const auto &Addr : ElfObject->getPltAddresses()) {
-      object::SymbolRef Sym(Addr.first, Object);
+      if (!Addr.first)
+        continue;
+      object::SymbolRef Sym(*Addr.first, Object);
       auto SymNameOrErr = Sym.getName();
       if (!SymNameOrErr)
         consumeError(SymNameOrErr.takeError());