[MachO] Pad section data to pointer size bytes

[pguo]

Summary

Pad macho section data to pointer size bytes, so that relocation table
and symbol table following section data will be pointer size aligned.

[gchatelet]

I don't know much about Mach object but code wise LGTM.
You should get approval from someone more knowledgeable than me though.

[pete]

LGTM.

This shouldn't affect the final binary size as the linker is going to probably recreate the relocations and symbol table anyway, but seems fine to align this more in the object files.

[pguo]

Thank you for your comments. And could you help me to commit the change since I haven't got the permission yet? Thanks.

[pguo]

• Fix unit test after changing macho pad bytes.

[pguo]

Update the patch, fixed unit test failure.

[gchatelet]

Do you intend to submit this patch?

[pguo]

Aditya has helped me to commit the patch. Thank you.

[gchatelet]

In D74273#2047609, @pguo wrote:

Aditya has helped me to commit the patch. Thank you.

If the patch is submitted already you should mark this patch as "Abandonned" and link to the commit in a comment. Thx!

[pguo]

In D74273#2062683, @gchatelet wrote:

In D74273#2047609, @pguo wrote:

Aditya has helped me to commit the patch. Thank you.

If the patch is submitted already you should mark this patch as "Abandonned" and link to the commit in a comment. Thx!

I see. Thank you.

[pguo]

Aditya helped to commit the change with commit ID: bdc3c73454

llvm/lib/MC/MachObjectWriter.cpp

for (const MCSection &Sec : Asm) {
 
     if (Sec.isVirtualSection())
       continue;
 
     SectionDataSize = std::max(SectionDataSize, Address + Size);
     SectionDataFileSize = std::max(SectionDataFileSize, Address + FileSize);
   }
 
-  // The section data is padded to 4 bytes.
+  // The section data is padded to pointer size bytes.
   //
   // FIXME: Is this machine dependent?
   unsigned SectionDataPadding =
-      offsetToAlignment(SectionDataFileSize, Align(4));
+      offsetToAlignment(SectionDataFileSize, is64Bit() ? Align(8) : Align(4));
   SectionDataFileSize += SectionDataPadding;
 
   // Write the prolog, starting with the header and load command...
   writeHeader(MachO::MH_OBJECT, NumLoadCommands, LoadCommandsSize,
               Asm.getSubsectionsViaSymbols());
   uint32_t Prot =
       MachO::VM_PROT_READ | MachO::VM_PROT_WRITE | MachO::VM_PROT_EXECUTE;
   writeSegmentLoadCommand("", NumSections, 0, VMSize, SectionDataStart,

llvm/test/MC/MachO/darwin-x86_64-diff-relocs.s

 // CHECK:   Section {
 // CHECK:     Index: 0
 // CHECK:     Name: __text (5F 5F 74 65 78 74 00 00 00 00 00 00 00 00 00 00)
 // CHECK:     Segment: __TEXT (5F 5F 54 45 58 54 00 00 00 00 00 00 00 00 00 00)
 // CHECK:     Address: 0x0
 // CHECK:     Size: 0x5E
 // CHECK:     Offset: 384
 // CHECK:     Alignment: 0
-// CHECK:     RelocationOffset: 0x26C
+// CHECK:     RelocationOffset: 0x270
 // CHECK:     RelocationCount: 12
 // CHECK:     Type: Regular (0x0)
 // CHECK:     Attributes [ (0x800004)
 // CHECK:       PureInstructions (0x800000)
 // CHECK:       SomeInstructions (0x4)
 // CHECK:     ]
 // CHECK:     Reserved1: 0x0
 // CHECK:     Reserved2: 0x0

 // CHECK:   Section {
 // CHECK:     Index: 1
 // CHECK:     Name: __data (5F 5F 64 61 74 61 00 00 00 00 00 00 00 00 00 00)
 // CHECK:     Segment: __DATA (5F 5F 44 41 54 41 00 00 00 00 00 00 00 00 00 00)
 // CHECK:     Address: 0x5E
 // CHECK:     Size: 0x8E
 // CHECK:     Offset: 478
 // CHECK:     Alignment: 0
-// CHECK:     RelocationOffset: 0x2CC
+// CHECK:     RelocationOffset: 0x2D0
 // CHECK:     RelocationCount: 16
 // CHECK:     Type: Regular (0x0)
 // CHECK:     Attributes [ (0x4)
 // CHECK:       SomeInstructions (0x4)
 // CHECK:     ]
 // CHECK:     Reserved1: 0x0
 // CHECK:     Reserved2: 0x0
 // CHECK:     Reserved3: 0x0

llvm/test/MC/MachO/variable-exprs.s

 // CHECK-X86_64:   Section {
 // CHECK-X86_64:     Index: 1
 // CHECK-X86_64:     Name: __data (5F 5F 64 61 74 61 00 00 00 00 00 00 00 00 00 00)
 // CHECK-X86_64:     Segment: __DATA (5F 5F 44 41 54 41 00 00 00 00 00 00 00 00 00 00)
 // CHECK-X86_64:     Address: 0x1
 // CHECK-X86_64:     Size: 0x38
 // CHECK-X86_64:     Offset: 385
 // CHECK-X86_64:     Alignment: 0
-// CHECK-X86_64:     RelocationOffset: 0x1BC
+// CHECK-X86_64:     RelocationOffset: 0x1C0
 // CHECK-X86_64:     RelocationCount: 9
 // CHECK-X86_64:     Type: Regular (0x0)
 // CHECK-X86_64:     Attributes [ (0x0)
 // CHECK-X86_64:     ]
 // CHECK-X86_64:     Reserved1: 0x0
 // CHECK-X86_64:     Reserved2: 0x0
 // CHECK-X86_64:     Reserved3: 0x0
 // CHECK-X86_64:     SectionData (