[llvm-readobj] - Don't crash when dumping .stack_sizes and unable to find a relocation resolver.

The crash might happen when we have either a broken or unsupported object
and trying to resolve relocations when dumping the .stack_sizes section.

For the test case I used a 32-bits ELF header and a 64-bit relocation.
In this case a null pointer is returned by the code instead of the relocation
resolver function and then we crash.

Differential revision: https://reviews.llvm.org/D67962

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@372838 91177308-0d34-0410-b5e6-96231b3b80d8

test/tools/llvm-readobj/stack-sizes.test

@@ -597,3 +597,29 @@ Symbols:
     Value:   0x10
     Type:    STT_FUNC
     Binding: STB_GLOBAL
+
+## Check that we report an error when we are unable to resolve a relocation for a given ELF architecture.
+## Here we have a 64-bit relocation used in a 32-bit object.
+
+# RUN: yaml2obj --docnum=12 %s > %t17
+# RUN: not llvm-readelf --stack-sizes %t17 2>&1 | FileCheck %s -DFILE=%t17 --check-prefix=UNSUPPRELOC2
+# RUN: not llvm-readobj --stack-sizes %t17 2>&1 | FileCheck %s -DFILE=%t17 --check-prefix=UNSUPPRELOC2
+
+# UNSUPPRELOC2: error: '[[FILE]]': unsupported relocation type in section .rela.stack_sizes: R_X86_64_64
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS32
+  Data:    ELFDATA2MSB
+  Type:    ET_REL
+  Machine: EM_X86_64
+Sections:
+  - Name: .stack_sizes
+    Type: SHT_PROGBITS
+    Content: "00"
+  - Name: .rela.stack_sizes
+    Type: SHT_RELA
+    Info: .stack_sizes
+    Relocations:
+      - Offset: 0
+        Type:   R_X86_64_64

tools/llvm-readobj/ELFDumper.cpp

@@ -4935,7 +4935,7 @@ void DumpStyle<ELFT>::printRelocatableStackSizes(
     auto Contents = unwrapOrError(this->FileName, StackSizesSec.getContents());
     DataExtractor Data(Contents, Obj->isLittleEndian(), sizeof(Elf_Addr));
     for (const RelocationRef &Reloc : RelocSec.relocations()) {
-      if (!IsSupportedFn(Reloc.getType()))
+      if (!IsSupportedFn || !IsSupportedFn(Reloc.getType()))
         reportError(createStringError(
                         object_error::parse_failed,
                         "unsupported relocation type in section %s: %s",