Fix for pr24346: arm asm label calculation error in sub

Some ARM instructions encode 32-bit immediates as a 8-bit integer (0-255)
and a 4-bit rotation (0-30, even) in its least significant 12 bits. The
original fixup, FK_Data_4, patches the instruction by the value bit-to-bit,
regardless of the encoding. For example, assuming the label L1 and L2 are
0x0 and 0x104 respectively, the following instruction:

  add r0, r0, #(L2 - L1) ; expects 0x104, i.e., 260

would be assembled to the following, which adds 1 to r0, instead of 260:

  e2800104 add r0, r0, #4, 2 ; equivalently 1

The new fixup kind fixup_arm_mod_imm takes care of the encoding:

  e2800f41 add r0, r0, #260

Patch by Ting-Yuan Huang!

llvm-svn: 265122

3 files changed, 16 insertions, 6 deletions

diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
index a0402d9b740..17856452b7c 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
@@ -95,6 +95,7 @@ const MCFixupKindInfo &ARMAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"fixup_arm_movw_lo16", 0, 20, 0},
       {"fixup_t2_movt_hi16", 0, 20, 0},
       {"fixup_t2_movw_lo16", 0, 20, 0},
+      {"fixup_arm_mod_imm", 0, 12, 0},
   };
   const static MCFixupKindInfo InfosBE[ARM::NumTargetFixupKinds] = {
       // This table *must* be in the order that the fixup_* kinds are defined in
@@ -142,6 +143,7 @@ const MCFixupKindInfo &ARMAsmBackend::getFixupKindInfo(MCFixupKind Kind) const {
       {"fixup_arm_movw_lo16", 12, 20, 0},
       {"fixup_t2_movt_hi16", 12, 20, 0},
       {"fixup_t2_movw_lo16", 12, 20, 0},
+      {"fixup_arm_mod_imm", 20, 12, 0},
   };
 
   if (Kind < FirstTargetFixupKind)
@@ -665,6 +667,13 @@ unsigned ARMAsmBackend::adjustFixupValue(const MCFixup &Fixup, uint64_t Value,
 
     return Value;
   }
+  case ARM::fixup_arm_mod_imm:
+    Value = ARM_AM::getSOImmVal(Value);
+    if (Ctx && Value >> 12) {
+      Ctx->reportError(Fixup.getLoc(), "out of range immediate fixup value");
+      return 0;
+    }
+    return Value;
   }
 }
 
@@ -731,6 +740,7 @@ static unsigned getFixupKindNumBytes(unsigned Kind) {
   case FK_Data_2:
   case ARM::fixup_arm_thumb_br:
   case ARM::fixup_arm_thumb_cb:
+  case ARM::fixup_arm_mod_imm:
     return 2;
 
   case ARM::fixup_arm_pcrel_10_unscaled:
@@ -809,6 +819,7 @@ static unsigned getFixupKindContainerSizeBytes(unsigned Kind) {
   case ARM::fixup_arm_movw_lo16:
   case ARM::fixup_t2_movt_hi16:
   case ARM::fixup_t2_movw_lo16:
+  case ARM::fixup_arm_mod_imm:
     // Instruction size is 4 bytes.
     return 4;
   }
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMFixupKinds.h b/llvm/lib/Target/ARM/MCTargetDesc/ARMFixupKinds.h
index 51dbe1449b6..3fe2302bdd3 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMFixupKinds.h
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMFixupKinds.h
@@ -107,6 +107,9 @@ enum Fixups {
   fixup_t2_movt_hi16, // :upper16:
   fixup_t2_movw_lo16, // :lower16:
 
+  // fixup_arm_mod_imm - Fixup for mod_imm
+  fixup_arm_mod_imm,
+
   // Marker
   LastTargetFixupKind,
   NumTargetFixupKinds = LastTargetFixupKind - FirstTargetFixupKind
diff --git a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
index 0a6c7a999cb..901ab45c2dc 100644
--- a/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
+++ b/llvm/lib/Target/ARM/MCTargetDesc/ARMMCCodeEmitter.cpp
@@ -317,12 +317,8 @@ public:
     // Support for fixups (MCFixup)
     if (MO.isExpr()) {
       const MCExpr *Expr = MO.getExpr();
-      // In instruction code this value always encoded as lowest 12 bits,
-      // so we don't have to perform any specific adjustments.
-      // Due to requirements of relocatable records we have to use FK_Data_4.
-      // See ARMELFObjectWriter::ExplicitRelSym and
-      //     ARMELFObjectWriter::GetRelocTypeInner for more details.
-      MCFixupKind Kind = MCFixupKind(FK_Data_4);
+      // Fixups resolve to plain values that need to be encoded.
+      MCFixupKind Kind = MCFixupKind(ARM::fixup_arm_mod_imm);
       Fixups.push_back(MCFixup::create(0, Expr, Kind, MI.getLoc()));
       return 0;
     }