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

[grimar]

Summary

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.

[grimar]

• Rewrote the comment.

[grimar]

• The same.

[jhenderson]

I'm beginning to think that stack-sizes.test needs breaking up into smaller tests...! This change LGTM anyway.

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

600

when we unable -> when we are unable

I'd also probably avoid unnecessarily abbreviating architecture to arch.

601

I'd probably just get rid of "valid" since a 64-bit relocation in a 32-bit object doesn't really make sense.

[MaskRay]

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

601

ELFCLASS32+EM_X86_64 can mean x32 ABI (x86_64-linux-gnux32), so not entirely "invalid"... Though it is of ELFDATA2MSB, the big-endian stuff makes it invalid.

[grimar]

In D67962#1682098, @jhenderson wrote:

I'm beginning to think that stack-sizes.test needs breaking up into smaller tests...!

I would probably start from splitting all the warning/error testing to stack-sizes-err.test.
They seem to take more than half (and still do not test all of the possible messages).

[jhenderson]

In D67962#1682178, @grimar wrote:

In D67962#1682098, @jhenderson wrote:

I'm beginning to think that stack-sizes.test needs breaking up into smaller tests...!

I would probably start from splitting all the warning/error testing to stack-sizes-err.test.
They seem to take more than half (and still do not test all of the possible messages).

That would be a good start. I'd probably split the warning/error testing further into related warnings though. For example, invalid relocations could be tested in their own test.

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

- Name:    .stack_sizes
     Content: "100000000000000010"
     Link:    .text
 Symbols:
   - Name:    _Z3foof
     Section: .text
     Value:   0x10
     Type:    STT_FUNC
     Binding: STB_GLOBAL
+
+## Check that we report an error when we find a relocation that has a valid type, but
+## cannot be resolved. Here we have a 32-bit object, but 64-bit relocation.
+
+# 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

const SectionRef FunctionSec = Obj->toSectionRef(unwrapOrError(
         this->FileName, EF->getSection(StackSizesELFSec->sh_link)));
 
     bool (*IsSupportedFn)(uint64_t);
     RelocationResolver Resolver;
     std::tie(IsSupportedFn, Resolver) = getRelocationResolver(*Obj);
     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",
                         getSectionName(RelocSec).data(),
                         EF->getRelocationTypeName(Reloc.getType()).data()),
                     Obj->getFileName());
       this->printStackSize(Obj, Reloc, FunctionSec, StackSizeSectionName,
                            Resolver, Data);