[yaml2obj] - Allow overriding sh_entsize for SHT_GNU_versym sections.

[grimar]

Summary

This allows to write a test case for one of untested errors
in llvm/Object/ELF.h.

I did it in this patch to demonstrate.

[MaskRay]

test/Object/invalid.test

610

How about moving this yaml document to test/tools/yaml2obj/versym-section.yaml?

tools/yaml2obj/yaml2elf.cpp

800

?: may be used here.

[grimar]

• Addressed review comments.

test/Object/invalid.test

610

But we have test/Object/invalid.test exactly to check the errors reported in llvm/Object/ELF.h.

I.e. this test checks the functionality of lib/Object, just like the other 28 tests around.
Seems it is a proper place to have it?

tools/yaml2obj/yaml2elf.cpp

800

Ok. Done.

[MaskRay]

tools/yaml2obj/yaml2elf.cpp

800

one pair of the parentheses can be deleted:)

include/llvm/Object/ELF.h

Expected<const T *> ELFFile<ELFT>::getEntry(uint32_t Section,
   return getEntry<T>(*SecOrErr, Entry);
 }
 
 template <class ELFT>
 template <typename T>
 Expected<const T *> ELFFile<ELFT>::getEntry(const Elf_Shdr *Section,
                                             uint32_t Entry) const {
   if (sizeof(T) != Section->sh_entsize)
-    // TODO: this error is untested.
-    return createError("invalid sh_entsize");
+    return createError("section " + getSecIndexForError(this, Section) +
+                       " has invalid sh_entsize: expected " + Twine(sizeof(T)) +
+                       ", but got " + Twine(Section->sh_entsize));
   size_t Pos = Section->sh_offset + Entry * sizeof(T);
   if (Pos + sizeof(T) > Buf.size())
     return createError("unable to access section " +
                        getSecIndexForError(this, Section) + " data at 0x" +
                        Twine::utohexstr(Pos) +
                        ": offset goes past the end of file");
   return reinterpret_cast<const T *>(base() + Pos);
 }

test/Object/invalid.test

 --- !ELF
 FileHeader:
   Class:    ELFCLASS64
   Data:     ELFDATA2LSB
   Type:     ET_REL
   Machine:  EM_X86_64
   SHOffset: 0xffffffffffffffff
 
 ## Check that llvm-objdump reports an error when it tries to dump a
 ## symbol name and .strtab is empty.
 
 # RUN: yaml2obj %s --docnum=29 -o %t29
 # RUN: not llvm-objdump -syms %t29 2>&1 | FileCheck -DFILE=%t29 --check-prefix=STRTAB-EMPTY2 %s
 
 # STRTAB-EMPTY2: error: '[[FILE]]': SHT_STRTAB string table section [index 1] is empty
 
 --- !ELF
 FileHeader:
   Class:   ELFCLASS64
   Data:    ELFDATA2LSB
   Type:    ET_DYN
   Machine: EM_X86_64
 Sections:
   - Name: .strtab
     Type: SHT_STRTAB
     Content: ""
 Symbols:
   - Name: foo
+
+## Check that we report an error if SHT_GNU_versym has invalid
+## sh_entsize value (3 instead of 2) when trying to access the entries.
+
+# RUN: yaml2obj %s --docnum=30 -o %t30
+# RUN: not llvm-readobj -V %t30 2>&1 | FileCheck --check-prefix=INVALID-VER-SHENTSIZE %s
+
+# INVALID-VER-SHENTSIZE: error: section [index 1] has invalid sh_entsize: expected 2, but got 3
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  OSABI:   ELFOSABI_FREEBSD
+  Type:    ET_DYN
+  Machine: EM_X86_64
+Sections:
+  - Name:    .gnu.version
+    Type:    SHT_GNU_versym
+    EntSize: 0x0000000000000003
+    Entries: [ ]
+## Needed to trigger creation of .dynsym.
+DynamicSymbols:
+  - Name:    foo
+    Binding: STB_GLOBAL

test/tools/yaml2obj/versym-section.yaml

-# RUN: yaml2obj %s -o %t
-# RUN: llvm-readobj -V %t | FileCheck %s
-
 ## Check we are able to produce a valid SHT_GNU_versym
 ## section from its description.
 
+# RUN: yaml2obj --docnum=1 %s -o %t1
+# RUN: llvm-readobj -V %t1 | FileCheck %s
+
 # CHECK:      Version symbols {
 # CHECK-NEXT:   Section Name: .gnu.version
 # CHECK-NEXT:   Address: 0x200210
 # CHECK-NEXT:   Offset: 0x240
 # CHECK-NEXT:   Link: 6
 # CHECK-NEXT:   Symbols [
 # CHECK-NEXT:     Symbol {
 # CHECK-NEXT:       Version: 0
Dependencies:
             Flags:           0
             Other:           4
 DynamicSymbols:
   - Name:    f1
     Binding: STB_GLOBAL
   - Name:    f2
     Binding: STB_GLOBAL
 ...
+
+## Check we are able to set custom sh_entsize field for SHT_GNU_versym section.
+
+# RUN: yaml2obj --docnum=2 %s -o %t2
+# RUN: llvm-readelf -S %t2 | FileCheck %s --check-prefix=ENTSIZE
+
+# ENTSIZE: Section Headers:
+# ENTSIZE:   [Nr] Name         Type   Address          Off    Size   ES
+# ENTSIZE:   [ 1] .gnu.version VERSYM 0000000000000000 000180 000000 03
+
+--- !ELF
+FileHeader:
+  Class:   ELFCLASS64
+  Data:    ELFDATA2LSB
+  OSABI:   ELFOSABI_FREEBSD
+  Type:    ET_DYN
+  Machine: EM_X86_64
+Sections:
+  - Name:    .gnu.version
+    Type:    SHT_GNU_versym
+    EntSize: 0x0000000000000003
+    Entries: [ ]

tools/yaml2obj/yaml2elf.cpp

 bool ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                          const ELFYAML::SymverSection &Section,
                                          ContiguousBlobAccumulator &CBA) {
   raw_ostream &OS =
       CBA.getOSAndAlignedOffset(SHeader.sh_offset, SHeader.sh_addralign);
   for (uint16_t Version : Section.Entries)
     support::endian::write<uint16_t>(OS, Version, ELFT::TargetEndianness);
 
-  SHeader.sh_entsize = 2;
+  SHeader.sh_entsize = Section.EntSize ? (uint64_t)(*Section.EntSize) : 2;
   SHeader.sh_size = Section.Entries.size() * SHeader.sh_entsize;
   return true;
 }
 
 template <class ELFT>
 bool ELFState<ELFT>::writeSectionContent(Elf_Shdr &SHeader,
                                          const ELFYAML::VerdefSection &Section,
                                          ContiguousBlobAccumulator &CBA) {
   typedef typename ELFT::Verdef Elf_Verdef;