[MIPS] Modify LongBranch expansion to work with sandboxing

lib/Target/Mips/MCTargetDesc/MipsAsmBackend.cpp

Index: lib/Target/Mips/MCTargetDesc/MipsAsmBackend.cpp
diff --git a/lib/Target/Mips/MCTargetDesc/MipsAsmBackend.cpp b/lib/Target/Mips/MCTargetDesc/MipsAsmBackend.cpp
index 50f0893fce7e2defdde30787b81c77bc3f361ea3..899c378ee603f467f94eb93d3ce9b6399cda2fd8 100644
--- a/lib/Target/Mips/MCTargetDesc/MipsAsmBackend.cpp
+++ b/lib/Target/Mips/MCTargetDesc/MipsAsmBackend.cpp
@@ -77,6 +77,21 @@ static unsigned adjustFixupValue(unsigned Kind, uint64_t Value) {
     // Get the 4th 16-bits.
     Value = ((Value + 0x800080008000LL) >> 48) & 0xffff;
     break;
+  // @LOCALMOD-START
+  case Mips::fixup_Mips_NACL_LONG_BRANCH_HI16:
+    // Resolve LUi part of the LUi/ADDiu long branch offset calculation.
+    // The Value is the offset of the target basic block from the LUi
+    // instruction. Since we need offset from the next instruction (ADDiu),
+    // we modify if by -4. Get the high 16-bits. Since the immediate from the
+    // ADDiu is treated as signed, add 1 if bit 15 is 1.
+    Value = ((Value - 4 + 0x8000) >> 16) & 0xffff;
+    break;
+  case Mips::fixup_Mips_NACL_LONG_BRANCH_LO16:
+    // Resolve ADDiu part of the LUi/ADDiu long branch offset calculation.
+    // Get the low 16-bits.
+    Value = Value & 0xffff;
+    break;
+  // @LOCALMOD-END
   }
 
   return Value;
@@ -98,6 +113,24 @@ public:
       MCELFObjectTargetWriter::getOSABI(OSType), IsLittle, Is64Bit);
   }
 
+  // @LOCALMOD-START
+  /// processFixupValue - Target hook to process the literal value of a fixup
+  /// if necessary.
+  void processFixupValue(const MCAssembler &Asm, const MCAsmLayout &Layout,
+                         const MCFixup &Fixup, const MCFragment *DF,
+                         MCValue &Target, uint64_t &Value,
+                         bool &IsResolved) {
+    if (OSType == Triple::NaCl) {

[Mark Seaborn, 2013/10/24 23:38:43]

Isn't this check unnecessary?  Checking getKind() below should be enough.

[petarj, 2013/11/21 18:23:42]

Done.

+      if ((unsigned)Fixup.getKind() == Mips::fixup_Mips_NACL_LONG_BRANCH_HI16
+          || ((unsigned)Fixup.getKind()
+              == Mips::fixup_Mips_NACL_LONG_BRANCH_LO16)) {
+        // We don't need to emit relocation for long branch fixup.
+        IsResolved = true;
+      }
+    }
+  }
+  // @LOCALMOD-END
+
   /// ApplyFixup - Apply the \p Value for given \p Fixup into the provided
   /// data fragment, at the offset specified by the fixup and following the
   /// fixup kind as appropriate.
@@ -189,7 +222,13 @@ public:
       { "fixup_Mips_GOT_HI16",     0,     16,   0 },
       { "fixup_Mips_GOT_LO16",     0,     16,   0 },
       { "fixup_Mips_CALL_HI16",    0,     16,   0 },
-      { "fixup_Mips_CALL_LO16",    0,     16,   0 }
+      { "fixup_Mips_CALL_LO16",    0,     16,   0 },
+      // @LOCALMOD-START
+      { "fixup_Mips_NACL_LONG_BRANCH_HI16",    0,     16,
+        MCFixupKindInfo::FKF_IsPCRel },
+      { "fixup_Mips_NACL_LONG_BRANCH_LO16",    0,     16,
+        MCFixupKindInfo::FKF_IsPCRel }
+      // @LOCALMOD-END
     };
 
     if (Kind < FirstTargetFixupKind)