[llvm-readobj] MachO -- correctly dump section field 'Reserved3'

[davide]

Summary

I stumbled upon this fileld while looking at macho-dump -- and it seems llvm-readobj completely ignores it. I wasn't able to gather many informations about it, I just see that MCWriter unconditionally sets this to zero only for 64-bits object.

Jim, Nick, I hope this is the right way of handling it. I'm also curious about what this is supposed to be used for :)

[• rafael]

Well, even it it has to always be 0, we have to be able to test its value, so LGTM.

[davide]

No objections :) Going to su
Still -- I'm curious if anybody more

[davide]

No objections :) Going to submit this now.
Still -- I'm curious if anybody more familiar with MachO can explain
what's the need of this field.

[grosbach]

Pretty sure it's just to force the structure size to be a multiple of 64-bits.

test/MC/AArch64/arm64-leaf-compact-unwind.s

 // CHECK-NEXT:   RelocationOffset:
 // CHECK-NEXT:   RelocationCount:
 // CHECK-NEXT:   Type:
 // CHECK-NEXT:   Attributes [
 // CHECK-NEXT:     Debug
 // CHECK-NEXT:   ]
 // CHECK-NEXT:   Reserved1:
 // CHECK-NEXT:   Reserved2:
+// CHECK-NEXT:   Reserved3:
 // CHECK-NEXT:   Relocations [
 // CHECK-NEXT:     Relocation {
 // CHECK-NEXT:       Offset: 0x60
 // CHECK-NEXT:       PCRel: 0
 // CHECK-NEXT:       Length: 3
 // CHECK-NEXT:       Type: ARM64_RELOC_UNSIGNED (0)
 // CHECK-NEXT:       Section: __text (1)
 // CHECK-NEXT:     }

test/tools/llvm-readobj/sections-ext.test

 MACHO-X86-64-NEXT:    RelocationCount: 3
 MACHO-X86-64-NEXT:    Type: 0x0
 MACHO-X86-64-NEXT:    Attributes [ (0x800004)
 MACHO-X86-64-NEXT:      PureInstructions (0x800000)
 MACHO-X86-64-NEXT:      SomeInstructions (0x4)
 MACHO-X86-64-NEXT:    ]
 MACHO-X86-64-NEXT:    Reserved1: 0x0
 MACHO-X86-64-NEXT:    Reserved2: 0x0
+MACHO-X86-64-NEXT:    Reserved3: 0x0
 MACHO-X86-64-NEXT:    Relocations [
 MACHO-X86-64-NEXT:      0xE 1 2 1 X86_64_RELOC_BRANCH 0 _SomeOtherFunction
 MACHO-X86-64-NEXT:      0x9 1 2 1 X86_64_RELOC_BRANCH 0 _puts
 MACHO-X86-64-NEXT:      0x4 1 2 1 X86_64_RELOC_SIGNED 0 L_.str
 MACHO-X86-64-NEXT:    ]
 MACHO-X86-64-NEXT:    Symbols [
 MACHO-X86-64-NEXT:      Symbol {
 MACHO-X86-64-NEXT:        Name: _main (1)

 MACHO-X86-64-NEXT:    Alignment: 0
 MACHO-X86-64-NEXT:    RelocationOffset: 0x0
 MACHO-X86-64-NEXT:    RelocationCount: 0
 MACHO-X86-64-NEXT:    Type: ExtReloc (0x2)
 MACHO-X86-64-NEXT:    Attributes [ (0x0)
 MACHO-X86-64-NEXT:    ]
 MACHO-X86-64-NEXT:    Reserved1: 0x0
 MACHO-X86-64-NEXT:    Reserved2: 0x0
+MACHO-X86-64-NEXT:    Reserved3: 0x0
 MACHO-X86-64-NEXT:    Relocations [
 MACHO-X86-64-NEXT:    ]
 MACHO-X86-64-NEXT:    Symbols [
 MACHO-X86-64-NEXT:      Symbol {
 MACHO-X86-64-NEXT:        Name: L_.str (32)
 MACHO-X86-64-NEXT:        Type: Section (0xE)
 MACHO-X86-64-NEXT:        Section: __cstring (0x2)
 MACHO-X86-64-NEXT:        RefType: UndefinedNonLazy (0x0)

 MACHO-PPC64-NEXT:     RelocationCount: 5
 MACHO-PPC64-NEXT:     Type: 0x0
 MACHO-PPC64-NEXT:     Attributes [ (0x800004)
 MACHO-PPC64-NEXT:       PureInstructions (0x800000)
 MACHO-PPC64-NEXT:       SomeInstructions (0x4)
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Reserved1: 0x0
 MACHO-PPC64-NEXT:     Reserved2: 0x0
+MACHO-PPC64-NEXT:     Reserved3: 0x0
 MACHO-PPC64-NEXT:     Relocations [
 MACHO-PPC64-NEXT:       Relocation {
 MACHO-PPC64-NEXT:         Offset: 0x24
 MACHO-PPC64-NEXT:         PCRel: 0
 MACHO-PPC64-NEXT:         Length: 2
 MACHO-PPC64-NEXT:         Type:  (14)
 MACHO-PPC64-NEXT:         Value: 0x64
 MACHO-PPC64-NEXT:       }

 MACHO-PPC64-NEXT:     RelocationCount: 4
 MACHO-PPC64-NEXT:     Type: 0x8
 MACHO-PPC64-NEXT:     Attributes [ (0x800004)
 MACHO-PPC64-NEXT:       PureInstructions (0x800000)
 MACHO-PPC64-NEXT:       SomeInstructions (0x4)
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Reserved1: 0x0
 MACHO-PPC64-NEXT:     Reserved2: 0x20
+MACHO-PPC64-NEXT:     Reserved3: 0x0
 MACHO-PPC64-NEXT:     Relocations [
 MACHO-PPC64-NEXT:       Relocation {
 MACHO-PPC64-NEXT:         Offset: 0x14
 MACHO-PPC64-NEXT:         PCRel: 0
 MACHO-PPC64-NEXT:         Length: 2
 MACHO-PPC64-NEXT:         Type:  (14)
 MACHO-PPC64-NEXT:         Value: 0x6C
 MACHO-PPC64-NEXT:       }

 MACHO-PPC64-NEXT:     Alignment: 2
 MACHO-PPC64-NEXT:     RelocationOffset: 0x0
 MACHO-PPC64-NEXT:     RelocationCount: 0
 MACHO-PPC64-NEXT:     Type: 0x0
 MACHO-PPC64-NEXT:     Attributes [ (0x0)
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Reserved1: 0x0
 MACHO-PPC64-NEXT:     Reserved2: 0x0
+MACHO-PPC64-NEXT:     Reserved3: 0x0
 MACHO-PPC64-NEXT:     Relocations [
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Symbols [
 MACHO-PPC64-NEXT:       Symbol {
 MACHO-PPC64-NEXT:         Name: _b (1)
 MACHO-PPC64-NEXT:         Extern
 MACHO-PPC64-NEXT:         Type: Section (0xE)
 MACHO-PPC64-NEXT:         Section: __data (0x3)

 MACHO-PPC64-NEXT:     Alignment: 2
 MACHO-PPC64-NEXT:     RelocationOffset: 0x0
 MACHO-PPC64-NEXT:     RelocationCount: 0
 MACHO-PPC64-NEXT:     Type: 0x6
 MACHO-PPC64-NEXT:     Attributes [ (0x0)
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Reserved1: 0x1
 MACHO-PPC64-NEXT:     Reserved2: 0x0
+MACHO-PPC64-NEXT:     Reserved3: 0x0
 MACHO-PPC64-NEXT:     Relocations [
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Symbols [
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     SectionData (
 MACHO-PPC64-NEXT:       0000: 00000000 00000000                    |........|
 MACHO-PPC64-NEXT:     )
 MACHO-PPC64-NEXT:   }
 MACHO-PPC64-NEXT:   Section {
 MACHO-PPC64-NEXT:     Index: 4
 MACHO-PPC64-NEXT:     Name: __la_symbol_ptr (5F 5F 6C 61 5F 73 79 6D 62 6F 6C 5F 70 74 72 00)
 MACHO-PPC64-NEXT:     Segment: __DATA (5F 5F 44 41 54 41 00 00 00 00 00 00 00 00 00 00)
 MACHO-PPC64-NEXT:     Address: 0x6C
 MACHO-PPC64-NEXT:     Size: 0x8
 MACHO-PPC64-NEXT:     Offset: 716
 MACHO-PPC64-NEXT:     Alignment: 2
 MACHO-PPC64-NEXT:     RelocationOffset: 0x31C
 MACHO-PPC64-NEXT:     RelocationCount: 1
 MACHO-PPC64-NEXT:     Type: 0x7
 MACHO-PPC64-NEXT:     Attributes [ (0x0)
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Reserved1: 0x2
 MACHO-PPC64-NEXT:     Reserved2: 0x0
+MACHO-PPC64-NEXT:     Reserved3: 0x0
 MACHO-PPC64-NEXT:     Relocations [
 MACHO-PPC64-NEXT:       Relocation {
 MACHO-PPC64-NEXT:         Offset: 0x0
 MACHO-PPC64-NEXT:         PCRel: 0
 MACHO-PPC64-NEXT:         Length: 3
 MACHO-PPC64-NEXT:         Type:  (0)
 MACHO-PPC64-NEXT:         Symbol: dyld_stub_binding_helper (5)
 MACHO-PPC64-NEXT:       }

test/tools/llvm-readobj/sections.test

 MACHO-X86-64-NEXT:    RelocationCount: 3
 MACHO-X86-64-NEXT:    Type: 0x0
 MACHO-X86-64-NEXT:    Attributes [ (0x800004)
 MACHO-X86-64-NEXT:      PureInstructions (0x800000)
 MACHO-X86-64-NEXT:      SomeInstructions (0x4)
 MACHO-X86-64-NEXT:    ]
 MACHO-X86-64-NEXT:    Reserved1: 0x0
 MACHO-X86-64-NEXT:    Reserved2: 0x0
+MACHO-X86-64-NEXT:    Reserved3: 0x0
 MACHO-X86-64-NEXT:  }
 MACHO-X86-64-NEXT:  Section {
 MACHO-X86-64-NEXT:    Index: 1
 MACHO-X86-64-NEXT:    Name: __cstring (5F 5F 63 73 74 72 69 6E 67 00 00 00 00 00 00 00)
 MACHO-X86-64-NEXT:    Segment: __TEXT (5F 5F 54 45 58 54 00 00 00 00 00 00 00 00 00 00)
 MACHO-X86-64-NEXT:    Address: 0x16
 MACHO-X86-64-NEXT:    Size: 0xD
 MACHO-X86-64-NEXT:    Offset: 390
 MACHO-X86-64-NEXT:    Alignment: 0
 MACHO-X86-64-NEXT:    RelocationOffset: 0x0
 MACHO-X86-64-NEXT:    RelocationCount: 0
 MACHO-X86-64-NEXT:    Type: ExtReloc (0x2)
 MACHO-X86-64-NEXT:    Attributes [ (0x0)
 MACHO-X86-64-NEXT:    ]
 MACHO-X86-64-NEXT:    Reserved1: 0x0
 MACHO-X86-64-NEXT:    Reserved2: 0x0
+MACHO-X86-64-NEXT:    Reserved3: 0x0
 MACHO-X86-64-NEXT:  }
 MACHO-X86-64-NEXT:]
 
 MACHO-PPC: Sections [
 MACHO-PPC-NEXT:   Section {
 MACHO-PPC-NEXT:     Index: 0
 MACHO-PPC-NEXT:     Name: __text (5F 5F 74 65 78 74 00 00 00 00 00 00 00 00 00 00)
 MACHO-PPC-NEXT:     Segment: __TEXT (5F 5F 54 45 58 54 00 00 00 00 00 00 00 00 00 00)

 MACHO-PPC64-NEXT:     RelocationCount: 5
 MACHO-PPC64-NEXT:     Type: 0x0
 MACHO-PPC64-NEXT:     Attributes [ (0x800004)
 MACHO-PPC64-NEXT:       PureInstructions (0x800000)
 MACHO-PPC64-NEXT:       SomeInstructions (0x4)
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Reserved1: 0x0
 MACHO-PPC64-NEXT:     Reserved2: 0x0
+MACHO-PPC64-NEXT:     Reserved3: 0x0
 MACHO-PPC64-NEXT:   }
 MACHO-PPC64-NEXT:   Section {
 MACHO-PPC64-NEXT:     Index: 1
 MACHO-PPC64-NEXT:     Name: __picsymbolstub1 (5F 5F 70 69 63 73 79 6D 62 6F 6C 73 74 75 62 31)
 MACHO-PPC64-NEXT:     Segment: __TEXT (5F 5F 54 45 58 54 00 00 00 00 00 00 00 00 00 00)
 MACHO-PPC64-NEXT:     Address: 0x40
 MACHO-PPC64-NEXT:     Size: 0x20
 MACHO-PPC64-NEXT:     Offset: 672
 MACHO-PPC64-NEXT:     Alignment: 5
 MACHO-PPC64-NEXT:     RelocationOffset: 0x2FC
 MACHO-PPC64-NEXT:     RelocationCount: 4
 MACHO-PPC64-NEXT:     Type: 0x8
 MACHO-PPC64-NEXT:     Attributes [ (0x800004)
 MACHO-PPC64-NEXT:       PureInstructions (0x800000)
 MACHO-PPC64-NEXT:       SomeInstructions (0x4)
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Reserved1: 0x0
 MACHO-PPC64-NEXT:     Reserved2: 0x20
+MACHO-PPC64-NEXT:     Reserved3: 0x0
 MACHO-PPC64-NEXT:   }
 MACHO-PPC64-NEXT:   Section {
 MACHO-PPC64-NEXT:     Index: 2
 MACHO-PPC64-NEXT:     Name: __data (5F 5F 64 61 74 61 00 00 00 00 00 00 00 00 00 00)
 MACHO-PPC64-NEXT:     Segment: __DATA (5F 5F 44 41 54 41 00 00 00 00 00 00 00 00 00 00)
 MACHO-PPC64-NEXT:     Address: 0x60
 MACHO-PPC64-NEXT:     Size: 0x4
 MACHO-PPC64-NEXT:     Offset: 704
 MACHO-PPC64-NEXT:     Alignment: 2
 MACHO-PPC64-NEXT:     RelocationOffset: 0x0
 MACHO-PPC64-NEXT:     RelocationCount: 0
 MACHO-PPC64-NEXT:     Type: 0x0
 MACHO-PPC64-NEXT:     Attributes [ (0x0)
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Reserved1: 0x0
 MACHO-PPC64-NEXT:     Reserved2: 0x0
+MACHO-PPC64-NEXT:     Reserved3: 0x0
 MACHO-PPC64-NEXT:   }
 MACHO-PPC64-NEXT:   Section {
 MACHO-PPC64-NEXT:     Index: 3
 MACHO-PPC64-NEXT:     Name: __nl_symbol_ptr (5F 5F 6E 6C 5F 73 79 6D 62 6F 6C 5F 70 74 72 00)
 MACHO-PPC64-NEXT:     Segment: __DATA (5F 5F 44 41 54 41 00 00 00 00 00 00 00 00 00 00)
 MACHO-PPC64-NEXT:     Address: 0x64
 MACHO-PPC64-NEXT:     Size: 0x8
 MACHO-PPC64-NEXT:     Offset: 708
 MACHO-PPC64-NEXT:     Alignment: 2
 MACHO-PPC64-NEXT:     RelocationOffset: 0x0
 MACHO-PPC64-NEXT:     RelocationCount: 0
 MACHO-PPC64-NEXT:     Type: 0x6
 MACHO-PPC64-NEXT:     Attributes [ (0x0)
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Reserved1: 0x1
 MACHO-PPC64-NEXT:     Reserved2: 0x0
+MACHO-PPC64-NEXT:     Reserved3: 0x0
 MACHO-PPC64-NEXT:   }
 MACHO-PPC64-NEXT:   Section {
 MACHO-PPC64-NEXT:     Index: 4
 MACHO-PPC64-NEXT:     Name: __la_symbol_ptr (5F 5F 6C 61 5F 73 79 6D 62 6F 6C 5F 70 74 72 00)
 MACHO-PPC64-NEXT:     Segment: __DATA (5F 5F 44 41 54 41 00 00 00 00 00 00 00 00 00 00)
 MACHO-PPC64-NEXT:     Address: 0x6C
 MACHO-PPC64-NEXT:     Size: 0x8
 MACHO-PPC64-NEXT:     Offset: 716
 MACHO-PPC64-NEXT:     Alignment: 2
 MACHO-PPC64-NEXT:     RelocationOffset: 0x31C
 MACHO-PPC64-NEXT:     RelocationCount: 1
 MACHO-PPC64-NEXT:     Type: 0x7
 MACHO-PPC64-NEXT:     Attributes [ (0x0)
 MACHO-PPC64-NEXT:     ]
 MACHO-PPC64-NEXT:     Reserved1: 0x2
 MACHO-PPC64-NEXT:     Reserved2: 0x0
+MACHO-PPC64-NEXT:     Reserved3: 0x0
 MACHO-PPC64-NEXT:   }
 MACHO-PPC64-NEXT: ]
 
 MACHO-ARM:      Sections [
 MACHO-ARM-NEXT:   Section {
 MACHO-ARM-NEXT:    Index: 0
 MACHO-ARM-NEXT:    Name: __text (5F 5F 74 65 78 74 00 00 00 00 00 00 00 00 00 00)
 MACHO-ARM-NEXT:    Segment: __TEXT (5F 5F 54 45 58 54 00 00 00 00 00 00 00 00 00 00)

tools/llvm-readobj/MachODumper.cpp

struct MachOSection {
     uint64_t Size;
     uint32_t Offset;
     uint32_t Alignment;
     uint32_t RelocationTableOffset;
     uint32_t NumRelocationTableEntries;
     uint32_t Flags;
     uint32_t Reserved1;
     uint32_t Reserved2;
+    uint32_t Reserved3;
   };
 
   struct MachOSymbol {
     uint32_t StringIndex;
     uint8_t Type;
     uint8_t SectionIndex;
     uint16_t Flags;
     uint64_t Value;
static void getSection(const MachOObjectFile *Obj,
   Section.Size        = Sect.size;
   Section.Offset      = Sect.offset;
   Section.Alignment   = Sect.align;
   Section.RelocationTableOffset = Sect.reloff;
   Section.NumRelocationTableEntries = Sect.nreloc;
   Section.Flags       = Sect.flags;
   Section.Reserved1   = Sect.reserved1;
   Section.Reserved2   = Sect.reserved2;
+  Section.Reserved3   = Sect.reserved3;
 }
 
 
 static void getSymbol(const MachOObjectFile *Obj,
                       DataRefImpl DRI,
                       MachOSymbol &Symbol) {
   if (!Obj->is64Bit()) {
     MachO::nlist Entry = Obj->getSymbolTableEntry(DRI);
for (const SectionRef &Section : Obj->sections()) {
     W.printHex("RelocationOffset", MOSection.RelocationTableOffset);
     W.printNumber("RelocationCount", MOSection.NumRelocationTableEntries);
     W.printEnum("Type", MOSection.Flags & 0xFF,
                 makeArrayRef(MachOSectionAttributes));
     W.printFlags("Attributes", MOSection.Flags >> 8,
                  makeArrayRef(MachOSectionAttributes));
     W.printHex("Reserved1", MOSection.Reserved1);
     W.printHex("Reserved2", MOSection.Reserved2);
+    if (Obj->is64Bit())
+      W.printHex("Reserved3", MOSection.Reserved3);
 
     if (opts::SectionRelocations) {
       ListScope D(W, "Relocations");
       for (const RelocationRef &Reloc : Section.relocations())
         printRelocation(Reloc);
     }
 
     if (opts::SectionSymbols) {