PNaCl: Fix negative relocation addends on x86-32

lib/Target/X86/MCTargetDesc/X86AsmBackend.cpp

 //===-- X86AsmBackend.cpp - X86 Assembler Backend -------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "MCTargetDesc/X86BaseInfo.h"
@@ skipping 81 matching lines @@
     return Infos[Kind - FirstTargetFixupKind];
   }
 
   void applyFixup(const MCFixup &Fixup, char *Data, unsigned DataSize,
                   uint64_t Value) const {
     unsigned Size = 1 << getFixupKindLog2Size(Fixup.getKind());
 
     assert(Fixup.getOffset() + Size <= DataSize &&
            "Invalid fixup offset!");
 
+    // @LOCALMOD-BEGIN
+    // This check breaks negative addends on x86-32.  It makes x86-32
+    // behaviour inconsistent with x86-64 and ARM.
+    // See: https://code.google.com/p/nativeclient/issues/detail?id=3548
+#if 0
     // Check that uppper bits are either all zeros or all ones.
     // Specifically ignore overflow/underflow as long as the leakage is
     // limited to the lower bits. This is to remain compatible with
     // other assemblers.
     assert(isIntN(Size * 8 + 1, Value) &&
            "Value does not fit in the Fixup field");
+#endif
+    // @LOCALMOD-END
 
     for (unsigned i = 0; i != Size; ++i)
       Data[Fixup.getOffset() + i] = uint8_t(Value >> (i * 8));
   }
 
   bool mayNeedRelaxation(const MCInst &Inst) const;
 
   bool fixupNeedsRelaxation(const MCFixup &Fixup,
                             uint64_t Value,
                             const MCRelaxableFragment *DF,
@@ skipping 381 matching lines @@
   if (TheTriple.isOSWindows() && TheTriple.getEnvironment() != Triple::ELF)
     return new WindowsX86AsmBackend(T, true, CPU);
 
   uint8_t OSABI = MCELFObjectTargetWriter::getOSABI(TheTriple.getOS());
   // @LOCALMOD-BEGIN
   if (TheTriple.isOSNaCl())
     return new NaClX86_64AsmBackend(T, OSABI, CPU);
   // @LOCALMOD-END
   return new ELFX86_64AsmBackend(T, OSABI, CPU);
 }