[MC] Implement support for R_X86_64_SIZE64

[davide]

Summary

Whilst looking at ELF X86_64 relocations in LLD, I noticed that MC lacks support for R_X86_64_SIZE{64,32}.
This is an attempt to implement the first one.
I blatantly copied the binutils syntax here, adding the '@SIZE' suffix. I hope it's fine, if there are concerns I'll be happy to discuss.
A patch for R_X86_64_SIZE32 will follow.

[majnemer]

Seems a little over specific, it would be nice if we could handle R_386_SIZE32 and R_X86_64_SIZE32 as well.

[majnemer]

In D7990#133275, @majnemer wrote:

Seems a little over specific, it would be nice if we could handle R_386_SIZE32 and R_X86_64_SIZE32 as well.

Arg, this feedback isn't very helpful. Sorry about that. I guess what I tried to communicate was that we should have a VK_SIZE instead of VK_X86_64_SIZE and let the fixup's kind govern whether we get `R_X86_64_SIZE32 or `R_X86_64_SIZE64.

[davide]

In D7990#133276, @majnemer wrote:

In D7990#133275, @majnemer wrote:

Seems a little over specific, it would be nice if we could handle R_386_SIZE32 and R_X86_64_SIZE32 as well.

Arg, this feedback isn't very helpful. Sorry about that. I guess what I tried to communicate was that we should have a VK_SIZE instead of VK_X86_64_SIZE and let the fixup's kind govern whether we get `R_X86_64_SIZE32 or `R_X86_64_SIZE64.

Thank for the review. This was my intention actually, and I think your comment is a sign that I chose the wording poorly.
Let me rephrase. It seems to me the format for VK is VK_<$arch | $format >_<$identifier>.
A couple of examples of this are, e.g. VK_Mips_HIGHEST and VK_COFF_IMGREL32
In other words, X86_64 doesn't refer to the size but the target architecture. We can use something else if you have a better proposition.

[• rafael]

I am with David. The point is that there are both arch specific and arch independent VK_*. Since there is also R_386_SIZE32 for the x86 arch, this should probably be just VK_SIZE.

[davide]

Addressed your comment. Are you fine with the rest of the patch?

[davide]

Patch with context.

[majnemer]

lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp

151

I would think this should be R_X86_64_SIZE32.

[• rafael]

Can you add a testcase for R_X86_64_SIZE32?

[davide]

Added support (and test) for SIZE32, fixed thinko spotted by David.

[• rafael]

LGTM

include/llvm/MC/MCExpr.h

enum VariantKind {
     VK_TLVP,      // Mach-O thread local variable relocations
     VK_TLVPPAGE,
     VK_TLVPPAGEOFF,
     VK_PAGE,
     VK_PAGEOFF,
     VK_GOTPAGE,
     VK_GOTPAGEOFF,
     VK_SECREL,
+    VK_SIZE,      // symbol@SIZE
     VK_WEAKREF,   // The link between the symbols in .weakref foo, bar
 
     VK_ARM_NONE,
     VK_ARM_TARGET1,
     VK_ARM_TARGET2,
     VK_ARM_PREL31,
     VK_ARM_SBREL,          // symbol(sbrel)
     VK_ARM_TLSLDO,         // symbol(tlsldo)

lib/MC/MCExpr.cpp

StringRef MCSymbolRefExpr::getVariantKindName(VariantKind Kind) {
   case VK_TLVP: return "TLVP";
   case VK_TLVPPAGE: return "TLVPPAGE";
   case VK_TLVPPAGEOFF: return "TLVPPAGEOFF";
   case VK_PAGE: return "PAGE";
   case VK_PAGEOFF: return "PAGEOFF";
   case VK_GOTPAGE: return "GOTPAGE";
   case VK_GOTPAGEOFF: return "GOTPAGEOFF";
   case VK_SECREL: return "SECREL32";
+  case VK_SIZE: return "SIZE";
   case VK_WEAKREF: return "WEAKREF";
   case VK_ARM_NONE: return "none";
   case VK_ARM_TARGET1: return "target1";
   case VK_ARM_TARGET2: return "target2";
   case VK_ARM_PREL31: return "prel31";
   case VK_ARM_SBREL: return "sbrel";
   case VK_ARM_TLSLDO: return "tlsldo";
   case VK_ARM_TLSCALL: return "tlscall";
return StringSwitch<VariantKind>(Name.lower())
     .Case("tlvppage", VK_TLVPPAGE)
     .Case("tlvppageoff", VK_TLVPPAGEOFF)
     .Case("page", VK_PAGE)
     .Case("pageoff", VK_PAGEOFF)
     .Case("gotpage", VK_GOTPAGE)
     .Case("gotpageoff", VK_GOTPAGEOFF)
     .Case("imgrel", VK_COFF_IMGREL32)
     .Case("secrel32", VK_SECREL)
+    .Case("size", VK_SIZE)
     .Case("l", VK_PPC_LO)
     .Case("h", VK_PPC_HI)
     .Case("ha", VK_PPC_HA)
     .Case("higher", VK_PPC_HIGHER)
     .Case("highera", VK_PPC_HIGHERA)
     .Case("highest", VK_PPC_HIGHEST)
     .Case("highesta", VK_PPC_HIGHESTA)
     .Case("got@l", VK_PPC_GOT_LO)

lib/Target/X86/MCTargetDesc/X86ELFObjectWriter.cpp

if (IsPCRel) {
           Type = ELF::R_X86_64_GOTOFF64;
           break;
         case MCSymbolRefExpr::VK_TPOFF:
           Type = ELF::R_X86_64_TPOFF64;
           break;
         case MCSymbolRefExpr::VK_DTPOFF:
           Type = ELF::R_X86_64_DTPOFF64;
           break;
+        case MCSymbolRefExpr::VK_SIZE:
+          Type = ELF::R_X86_64_SIZE64;
+          break;
         }
         break;
       case X86::reloc_signed_4byte:
         switch (Modifier) {
         default:
           llvm_unreachable("Unimplemented");
         case MCSymbolRefExpr::VK_None:
           Type = ELF::R_X86_64_32S;
           break;
         case MCSymbolRefExpr::VK_GOT:
           Type = ELF::R_X86_64_GOT32;
           break;
         case MCSymbolRefExpr::VK_GOTPCREL:
           Type = ELF::R_X86_64_GOTPCREL;
           break;
         case MCSymbolRefExpr::VK_TPOFF:
           Type = ELF::R_X86_64_TPOFF32;
           break;
         case MCSymbolRefExpr::VK_DTPOFF:
           Type = ELF::R_X86_64_DTPOFF32;
           break;
+        case MCSymbolRefExpr::VK_SIZE:
+          Type = ELF::R_X86_64_SIZE32;
+          break;
         }
         break;
       case FK_Data_4:
         Type = ELF::R_X86_64_32;
         break;
       case FK_Data_2: Type = ELF::R_X86_64_16; break;
       case FK_PCRel_1:
       case FK_Data_1: Type = ELF::R_X86_64_8; break;

test/MC/ELF/relocation.s

.long bar                         # R_X86_64_32
   zed = foo +2
   call zed@PLT
 
         leaq    -1+foo(%rip), %r11
 
         movl  $_GLOBAL_OFFSET_TABLE_, %eax
         movabs  $_GLOBAL_OFFSET_TABLE_, %rax
 
+        .quad    blah@SIZE                        # R_X86_64_SIZE64
+        .quad    blah@SIZE + 32                   # R_X86_64_SIZE64
+        .quad    blah@SIZE - 32                   # R_X86_64_SIZE64
+         movl    blah@SIZE, %eax                  # R_X86_64_SIZE32
+         movl    blah@SIZE + 32, %eax             # R_X86_64_SIZE32
+         movl    blah@SIZE - 32, %eax             # R_X86_64_SIZE32
+
 // CHECK:        Section {
 // CHECK:          Name: .rela.text
 // CHECK:          Relocations [
 // CHECK-NEXT:       0x1 R_X86_64_32        .text
 // CHECK-NEXT:       0x8 R_X86_64_32S       .text
 // CHECK-NEXT:       0x13 R_X86_64_32S      .text
 // CHECK-NEXT:       0x1A R_X86_64_32S      .text
 // CHECK-NEXT:       0x22 R_X86_64_32S      .text

 // CHECK-NEXT:       0x7B R_X86_64_DTPOFF64 foo 0x0
 // CHECK-NEXT:       0x85 R_X86_64_TPOFF64 baz 0x0
 // CHECK-NEXT:       0x8D R_X86_64_PC16 foo 0x8D
 // CHECK-NEXT:       0x8F R_X86_64_PC8 foo 0x8F
 // CHECK-NEXT:       0x91 R_X86_64_PLT32 zed 0xFFFFFFFFFFFFFFFC
 // CHECK-NEXT:       0x98 R_X86_64_PC32 foo 0xFFFFFFFFFFFFFFFB
 // CHECK-NEXT:       0x9D R_X86_64_GOTPC32 _GLOBAL_OFFSET_TABLE_ 0x1
 // CHECK-NEXT:       0xA3 R_X86_64_GOTPC64 _GLOBAL_OFFSET_TABLE_ 0x2
+// CHECK-NEXT:       0xAB R_X86_64_SIZE64 blah 0x0
+// CHECK-NEXT:       0xB3 R_X86_64_SIZE64 blah 0x20
+// CHECK-NEXT:       0xBB R_X86_64_SIZE64 blah 0xFFFFFFFFFFFFFFE0
+// CHECK-NEXT:       0xC6 R_X86_64_SIZE32 blah 0x0
+// CHECK-NEXT:       0xCD R_X86_64_SIZE32 blah 0x20
+// CHECK-NEXT:       0xD4 R_X86_64_SIZE32 blah 0xFFFFFFFFFFFFFFE0
 // CHECK-NEXT:     ]
 // CHECK-NEXT:   }
 
 // CHECK:        Symbol {
 // CHECK:          Name: .text (0)
 // CHECK-NEXT:     Value:
 // CHECK-NEXT:     Size:
 // CHECK-NEXT:     Binding: Local
 // CHECK-NEXT:     Type: Section
 // CHECK-NEXT:     Other: 0
 // CHECK-NEXT:     Section: .text (0x1)
 // CHECK-NEXT:   }