[obj2yaml] - Zero initialize program headers. NFCI.

[grimar]

Summary

It allows to simplify the current code and also
might help for the code around.

It is also consistent with what we do for another headers,
e.g. section headers, ELF header etc.

[MaskRay]

section headers, elf file header etc.

The canonical name for elf file header is "ELF header".

[jhenderson]

LGTM, with one suggestion.

llvm/lib/ObjectYAML/ELFEmitter.cpp

764

Maybe worth pulling Fragments.front().Offset into a variable so that you don't have to repeat its call three times?

[grimar]

llvm/lib/ObjectYAML/ELFEmitter.cpp

764

OK, will do.

[grimar]

llvm/lib/ObjectYAML/ELFEmitter.cpp

764

Ah, no, sorry, I can't do it. Otherwise we need to return the following line:

uint64_t PhdrFileOffset = Fragments.empty() ? 0 : Fragments.front().Offset;

i.e. need to check that Fragments is not empty again. This is probably a bit more complicated than inlining it.

[grimar]

llvm/lib/ObjectYAML/ELFEmitter.cpp

764

I.e. it would just revert all changes done by this patch here. As an alternative I can abandon this patch and just add zero(Phdr); in D78628.
What do you think?

[jhenderson]

llvm/lib/ObjectYAML/ELFEmitter.cpp

764

It's fine. It was only a suggestion. Happy for it to go in as is.

llvm/lib/ObjectYAML/ELFEmitter.cpp

void ELFState<ELFT>::writeELFHeader(ContiguousBlobAccumulator &CBA, raw_ostream &OS) {
 
   OS.write((const char *)&Header, sizeof(Header));
 }
 
 template <class ELFT>
 void ELFState<ELFT>::initProgramHeaders(std::vector<Elf_Phdr> &PHeaders) {
   for (const auto &YamlPhdr : Doc.ProgramHeaders) {
     Elf_Phdr Phdr;
+    zero(Phdr);
     Phdr.p_type = YamlPhdr.Type;
     Phdr.p_flags = YamlPhdr.Flags;
     Phdr.p_vaddr = YamlPhdr.VAddr;
     Phdr.p_paddr = YamlPhdr.PAddr;
     PHeaders.push_back(Phdr);
   }
 }
 
for (auto &YamlPhdr : Doc.ProgramHeaders) {
     Elf_Phdr &PHeader = PHeaders[PhdrIdx++];
     std::vector<Fragment> Fragments = getPhdrFragments(YamlPhdr, SHeaders);
     if (!llvm::is_sorted(Fragments, [](const Fragment &A, const Fragment &B) {
           return A.Offset < B.Offset;
         }))
       reportError("sections in the program header with index " +
                   Twine(PhdrIdx) + " are not sorted by their file offset");
 
-    uint64_t PhdrFileOffset = Fragments.empty() ? 0 : Fragments.front().Offset;
     if (YamlPhdr.Offset) {
-      if (!Fragments.empty() && *YamlPhdr.Offset > PhdrFileOffset)
+      if (!Fragments.empty() && *YamlPhdr.Offset > Fragments.front().Offset)
         reportError("'Offset' for segment with index " + Twine(PhdrIdx) +
                     " must be less than or equal to the minimum file offset of "
                     "all included sections (0x" +
-                    Twine::utohexstr(PhdrFileOffset) + ")");
-      PhdrFileOffset = *YamlPhdr.Offset;
+                    Twine::utohexstr(Fragments.front().Offset) + ")");
+      PHeader.p_offset = *YamlPhdr.Offset;
+    } else if (!Fragments.empty()) {
+      PHeader.p_offset = Fragments.front().Offset;
     }
-    PHeader.p_offset = PhdrFileOffset;
 
     // Find the maximum offset of the end of a section in order to set p_filesz
     // and p_memsz. When setting p_filesz, trailing SHT_NOBITS sections are not
     // counted.
     uint64_t FileOffset = PHeader.p_offset, MemOffset = PHeader.p_offset;
     for (const Fragment &F : Fragments) {
       uint64_t End = F.Offset + F.Size;
       MemOffset = std::max(MemOffset, End);