From a08b587494a09a94a72245dd9d7088564e511f4e Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Tue, 16 Feb 2010 05:03:17 +0000
Subject: [PATCH] make pcrel immediate values relative to the start of the
 field, not the end of the field, fixing rdar://7651978

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96330 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Target/X86/X86MCCodeEmitter.cpp        | 16 +++++++++++++---
 test/MC/AsmParser/X86/x86_64-new-encoder.s | 10 +++++-----
 2 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/lib/Target/X86/X86MCCodeEmitter.cpp b/lib/Target/X86/X86MCCodeEmitter.cpp
index d0ec0de6913..3f18696d855 100644
--- a/lib/Target/X86/X86MCCodeEmitter.cpp
+++ b/lib/Target/X86/X86MCCodeEmitter.cpp
@@ -153,14 +153,25 @@ EmitImmediate(const MCOperand &DispOp, unsigned Size, MCFixupKind FixupKind,
   // If this is a simple integer displacement that doesn't require a relocation,
   // emit it now.
   if (DispOp.isImm()) {
+    // FIXME: is this right for pc-rel encoding??  Probably need to emit this as
+    // a fixup if so.
     EmitConstant(DispOp.getImm()+ImmOffset, Size, CurByte, OS);
     return;
   }
 
   // If we have an immoffset, add it to the expression.
   const MCExpr *Expr = DispOp.getExpr();
+  
+  // If the fixup is pc-relative, we need to bias the value to be relative to
+  // the start of the field, not the end of the field.
+  if (FixupKind == MCFixupKind(X86::reloc_pcrel_4byte) ||
+      FixupKind == MCFixupKind(X86::reloc_riprel_4byte))
+    ImmOffset -= 4;
+  if (FixupKind == MCFixupKind(X86::reloc_pcrel_1byte))
+    ImmOffset -= 1;
+  
   if (ImmOffset)
-    Expr = MCBinaryExpr::CreateAdd(Expr,MCConstantExpr::Create(ImmOffset, Ctx),
+    Expr = MCBinaryExpr::CreateAdd(Expr, MCConstantExpr::Create(ImmOffset, Ctx),
                                    Ctx);
   
   // Emit a symbolic constant as a fixup and 4 zeros.
@@ -192,6 +203,7 @@ void X86MCCodeEmitter::EmitMemModRMByte(const MCInst &MI, unsigned Op,
     // the size of the immediate field.  If we have this case, add it into the
     // expression to emit.
     int ImmSize = X86II::hasImm(TSFlags) ? X86II::getSizeOfImm(TSFlags) : 0;
+    
     EmitImmediate(Disp, 4, MCFixupKind(X86::reloc_riprel_4byte),
                   CurByte, OS, Fixups, -ImmSize);
     return;
@@ -616,8 +628,6 @@ EncodeInstruction(const MCInst &MI, raw_ostream &OS,
   
   // If there is a remaining operand, it must be a trailing immediate.  Emit it
   // according to the right size for the instruction.
-  // FIXME: This should pass in whether the value is pc relative or not.  This
-  // information should be aquired from TSFlags as well.
   if (CurOp != NumOps)
     EmitImmediate(MI.getOperand(CurOp++),
                   X86II::getSizeOfImm(TSFlags), getImmFixupKind(TSFlags),
diff --git a/test/MC/AsmParser/X86/x86_64-new-encoder.s b/test/MC/AsmParser/X86/x86_64-new-encoder.s
index 7536a014148..56ec0b38994 100644
--- a/test/MC/AsmParser/X86/x86_64-new-encoder.s
+++ b/test/MC/AsmParser/X86/x86_64-new-encoder.s
@@ -3,24 +3,24 @@
 movl	foo(%rip), %eax
 // CHECK: movl	foo(%rip), %eax
 // CHECK: encoding: [0x8b,0x05,A,A,A,A]
-// CHECK: fixup A - offset: 2, value: foo, kind: reloc_riprel_4byte
+// CHECK: fixup A - offset: 2, value: foo-4, kind: reloc_riprel_4byte
 
 movb	$12, foo(%rip)
 // CHECK: movb	$12, foo(%rip)
 // CHECK: encoding: [0xc6,0x05,A,A,A,A,0x0c]
-// CHECK:    fixup A - offset: 2, value: foo-1, kind: reloc_riprel_4byte
+// CHECK:    fixup A - offset: 2, value: foo-5, kind: reloc_riprel_4byte
 
 movw	$12, foo(%rip)
 // CHECK: movw	$12, foo(%rip)
 // CHECK: encoding: [0x66,0xc7,0x05,A,A,A,A,0x0c,0x00]
-// CHECK:    fixup A - offset: 3, value: foo-2, kind: reloc_riprel_4byte
+// CHECK:    fixup A - offset: 3, value: foo-6, kind: reloc_riprel_4byte
 
 movl	$12, foo(%rip)
 // CHECK: movl	$12, foo(%rip)
 // CHECK: encoding: [0xc7,0x05,A,A,A,A,0x0c,0x00,0x00,0x00]
-// CHECK:    fixup A - offset: 2, value: foo-4, kind: reloc_riprel_4byte
+// CHECK:    fixup A - offset: 2, value: foo-8, kind: reloc_riprel_4byte
 
 movq	$12, foo(%rip)
 // CHECK:  movq	$12, foo(%rip)
 // CHECK: encoding: [0x48,0xc7,0x05,A,A,A,A,0x0c,0x00,0x00,0x00]
-// CHECK:    fixup A - offset: 3, value: foo-4, kind: reloc_riprel_4byte
+// CHECK:    fixup A - offset: 3, value: foo-8, kind: reloc_riprel_4byte
-- 
2.34.1