[llvm] r334515 - [MC] [X86] Teach leaq _GLOBAL_OFFSET_TABLE(%rip), %r15 to use R_X86_64_GOTPC32 instead of R_X86_64_PC32

[Fangrui Song via llvm-commits]

Author: maskray
Date: Tue Jun 12 09:20:44 2018
New Revision: 334515

URL: http://llvm.org/viewvc/llvm-project?rev=334515&view=rev
Log:
[MC] [X86] Teach leaq _GLOBAL_OFFSET_TABLE(%rip), %r15 to use R_X86_64_GOTPC32 instead of R_X86_64_PC32

Summary:
This is similar to D46319 (ARM). x86-64 psABI p40 gives an example:

  leaq _GLOBAL_OFFSET_TABLE(%rip), %r15 # GOTPC32 reloc

GNU as creates R_X86_64_GOTPC32. However, MC currently emits R_X86_64_PC32.

Reviewers: javed.absar, echristo

Subscribers: kristof.beyls, llvm-commits, peter.smith, grimar

Differential Revision: https://reviews.llvm.org/D47507

Modified:
    llvm/trunk/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
    llvm/trunk/test/MC/ELF/relocation.s

Modified: llvm/trunk/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp?rev=334515&r1=334514&r2=334515&view=diff
==============================================================================
--- llvm/trunk/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp (original)
+++ llvm/trunk/lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp Tue Jun 12 09:20:44 2018
@@ -350,8 +350,14 @@ EmitImmediate(const MCOperand &DispOp, S
       FixupKind == MCFixupKind(X86::reloc_riprel_4byte_movq_load) ||
       FixupKind == MCFixupKind(X86::reloc_riprel_4byte_relax) ||
       FixupKind == MCFixupKind(X86::reloc_riprel_4byte_relax_rex) ||
-      FixupKind == MCFixupKind(X86::reloc_branch_4byte_pcrel))
+      FixupKind == MCFixupKind(X86::reloc_branch_4byte_pcrel)) {
     ImmOffset -= 4;
+    // If this is a pc-relative load off _GLOBAL_OFFSET_TABLE_:
+    // leaq _GLOBAL_OFFSET_TABLE_(%rip), %r15
+    // this needs to be a GOTPC32 relocation.
+    if (StartsWithGlobalOffsetTable(Expr) != GOT_None)
+      FixupKind = MCFixupKind(X86::reloc_global_offset_table);
+  }
   if (FixupKind == FK_PCRel_2)
     ImmOffset -= 2;
   if (FixupKind == FK_PCRel_1)

Modified: llvm/trunk/test/MC/ELF/relocation.s
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/MC/ELF/relocation.s?rev=334515&r1=334514&r2=334515&view=diff
==============================================================================
--- llvm/trunk/test/MC/ELF/relocation.s (original)
+++ llvm/trunk/test/MC/ELF/relocation.s Tue Jun 12 09:20:44 2018
@@ -39,6 +39,8 @@ bar:
 
         leaq    -1+foo(%rip), %r11
 
+        leaq  _GLOBAL_OFFSET_TABLE_(%rax), %r15
+        leaq  _GLOBAL_OFFSET_TABLE_(%rip), %r15
         movl  $_GLOBAL_OFFSET_TABLE_, %eax
         movabs  $_GLOBAL_OFFSET_TABLE_, %rax
 
@@ -94,18 +96,20 @@ weak_sym:
 // 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:       0xD8 R_X86_64_GOTPCREL foo 0x0
-// CHECK-NEXT:       0xDC R_X86_64_PLT32 foo 0x0
-// CHECK-NEXT:       0xF0 R_X86_64_32 .text 0xF0
-// CHECK-NEXT:       0xF5 R_X86_64_PC16 pr23771 0xFFFFFFFFFFFFFFFE
-// CHECK-NEXT:       0xF7 R_X86_64_PC32 pr23272 0x0
+// CHECK-NEXT:       0x9F R_X86_64_GOTPC32 _GLOBAL_OFFSET_TABLE_ 0x3
+// CHECK-NEXT:       0xA6 R_X86_64_GOTPC32 _GLOBAL_OFFSET_TABLE_ 0xFFFFFFFFFFFFFFFC
+// CHECK-NEXT:       0xAB R_X86_64_GOTPC32 _GLOBAL_OFFSET_TABLE_ 0x1
+// CHECK-NEXT:       0xB1 R_X86_64_GOTPC64 _GLOBAL_OFFSET_TABLE_ 0x2
+// CHECK-NEXT:       0xB9 R_X86_64_SIZE64 blah 0x0
+// CHECK-NEXT:       0xC1 R_X86_64_SIZE64 blah 0x20
+// CHECK-NEXT:       0xC9 R_X86_64_SIZE64 blah 0xFFFFFFFFFFFFFFE0
+// CHECK-NEXT:       0xD4 R_X86_64_SIZE32 blah 0x0
+// CHECK-NEXT:       0xDB R_X86_64_SIZE32 blah 0x20
+// CHECK-NEXT:       0xE2 R_X86_64_SIZE32 blah 0xFFFFFFFFFFFFFFE0
+// CHECK-NEXT:       0xE6 R_X86_64_GOTPCREL foo 0x0
+// CHECK-NEXT:       0xEA R_X86_64_PLT32 foo 0x0
+// CHECK-NEXT:       0xFE R_X86_64_32 .text 0xFE
+// CHECK-NEXT:       0x103 R_X86_64_PC16 pr23771 0xFFFFFFFFFFFFFFFE
+// CHECK-NEXT:       0x105 R_X86_64_PC32 pr23272 0x0
 // CHECK-NEXT:     ]
 // CHECK-NEXT:   }