[yaml2obj][ELF] Add support for setting alignment in program headers

[jakehehrlich]

Summary

Sometimes program headers have larger alignments than any of the sections they contain. Currently yaml2obj can't produce such files. A bug recently appeared in llvm-objcopy that failed in such a case. I'd like to be able to add tests to llvm-objcopy for such cases.

This change adds an optional alignment parameter to program headers that will be used instead of calculating the alignment.

[jakehehrlich]

Rafael recommended that I split this into two separate changes. This change makes that split by removing the if-statment change that fixed default alignment.

[jakehehrlich]

ping, I haven't heard back on this yet.

llvm/trunk/include/llvm/ObjectYAML/ELFYAML.h

struct SectionName {
   StringRef Section;
 };
 
 struct ProgramHeader {
   ELF_PT Type;
   ELF_PF Flags;
   llvm::yaml::Hex64 VAddr;
   llvm::yaml::Hex64 PAddr;
+  Optional<llvm::yaml::Hex64> Align;
   std::vector<SectionName> Sections;
 };
 
 struct Symbol {
   StringRef Name;
   ELF_STT Type;
   StringRef Section;
   Optional<ELF_SHN> Index;

llvm/trunk/lib/ObjectYAML/ELFYAML.cpp

 
 void MappingTraits<ELFYAML::ProgramHeader>::mapping(
     IO &IO, ELFYAML::ProgramHeader &Phdr) {
   IO.mapRequired("Type", Phdr.Type);
   IO.mapOptional("Flags", Phdr.Flags, ELFYAML::ELF_PF(0));
   IO.mapOptional("Sections", Phdr.Sections);
   IO.mapOptional("VAddr", Phdr.VAddr, Hex64(0));
   IO.mapOptional("PAddr", Phdr.PAddr, Hex64(0));
+  IO.mapOptional("Align", Phdr.Align);
 }
 
 namespace {
 
 struct NormalizedOther {
   NormalizedOther(IO &)
       : Visibility(ELFYAML::ELF_STV(0)), Other(ELFYAML::ELF_STO(0)) {}
   NormalizedOther(IO &, uint8_t Original)

llvm/trunk/test/tools/yaml2obj/program-header-align.yaml

+# RUN: yaml2obj %s -o %t
+# RUN: llvm-readobj -program-headers %t | FileCheck %s
+
+!ELF
+FileHeader:
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  Type:            ET_EXEC
+  Machine:         EM_X86_64
+Sections:
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x0000000000000008
+    Content:         "00000000"
+  - Name:            .data
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    Content:         "00000000"
+    AddressAlign:    0x0000000000000010
+ProgramHeaders:
+  - Type: PT_LOAD
+    Flags: [ PF_X, PF_R ]
+    VAddr: 0xAAAA1030
+    PAddr: 0xFFFF1030
+    Align: 0x1000
+    Sections:
+      - Section: .text
+  - Type: PT_LOAD
+    Flags: [ PF_R ]
+    VAddr: 0xAAAA2040
+    PAddr: 0xFFFF2040
+    Align: 0x1000
+    Sections:
+      - Section: .data
+
+#CHECK:     ProgramHeaders [
+#CHECK-NEXT:   ProgramHeader {
+#CHECK-NEXT:    Type: PT_LOAD
+#CHECK-NEXT:    Offset: 0x230
+#CHECK-NEXT:    VirtualAddress: 0xAAAA1030
+#CHECK-NEXT:    PhysicalAddress: 0xFFFF1030
+#CHECK-NEXT:    FileSize: 4
+#CHECK-NEXT:    MemSize: 4
+#CHECK-NEXT:    Flags [
+#CHECK-NEXT:      PF_R
+#CHECK-NEXT:      PF_X
+#CHECK-NEXT:    ]
+#CHECK-NEXT:    Alignment: 4096
+#CHECK-NEXT:  }
+#CHECK-NEXT:  ProgramHeader {
+#CHECK-NEXT:    Type: PT_LOAD
+#CHECK-NEXT:    Offset: 0x240
+#CHECK-NEXT:    VirtualAddress: 0xAAAA2040
+#CHECK-NEXT:    PhysicalAddress: 0xFFFF2040
+#CHECK-NEXT:    FileSize: 4
+#CHECK-NEXT:    MemSize: 4
+#CHECK-NEXT:    Flags [
+#CHECK-NEXT:      PF_R
+#CHECK-NEXT:    ]
+#CHECK-NEXT:    Alignment: 4096
+#CHECK-NEXT:  }
+#CHECK-NEXT:]

llvm/trunk/tools/yaml2obj/yaml2elf.cpp

for (auto SecName : YamlPhdr.Sections) {
       uint32_t Index = 0;
       SN2I.lookup(SecName.Section, Index);
       const auto &SHeader = SHeaders[Index];
       if (SHeader.sh_offset == PHeader.p_offset + PHeader.p_filesz)
         PHeader.p_memsz += SHeader.sh_size;
     }
 
     // Set the alignment of the segment to be the same as the maximum alignment
-    // of the the sections with the same offset so that by default the segment
+    // of the sections with the same offset so that by default the segment
     // has a valid and sensible alignment.
+    if (YamlPhdr.Align) {
+      PHeader.p_align = *YamlPhdr.Align;
+    } else {
       PHeader.p_align = 1;
       for (auto SecName : YamlPhdr.Sections) {
         uint32_t Index = 0;
         SN2I.lookup(SecName.Section, Index);
         const auto &SHeader = SHeaders[Index];
         if (SHeader.sh_offset == PHeader.p_offset)
           PHeader.p_align = std::max(PHeader.p_align, SHeader.sh_addralign);
       }
     }
   }
+}
 
 template <class ELFT>
 void ELFState<ELFT>::addSymbols(const std::vector<ELFYAML::Symbol> &Symbols,
                                 std::vector<Elf_Sym> &Syms,
                                 unsigned SymbolBinding) {
   for (const auto &Sym : Symbols) {
     Elf_Sym Symbol;
     zero(Symbol);