Use the correct V8_HOST_ARCH macro, it is IA32 and not X86.

src/platform-linux.cc

 // Copyright 2006-2008 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 582 matching lines @@
   if (signal != SIGPROF) return;
   if (active_sampler_ == NULL) return;
 
   TickSample sample;
 
   // If profiling, we extract the current pc and sp.
   if (active_sampler_->IsProfiling()) {
     // Extracting the sample from the context is extremely machine dependent.
     ucontext_t* ucontext = reinterpret_cast<ucontext_t*>(context);
     mcontext_t& mcontext = ucontext->uc_mcontext;
-#if V8_HOST_ARCH_X86
+#if V8_HOST_ARCH_IA32
     sample.pc = mcontext.gregs[REG_EIP];
     sample.sp = mcontext.gregs[REG_ESP];
     sample.fp = mcontext.gregs[REG_EBP];
 #elif V8_HOST_ARCH_X64
     UNIMPLEMENTED();
     sample.pc = mcontext.gregs[REG_RIP];
     sample.sp = mcontext.gregs[REG_RSP];
     sample.fp = mcontext.gregs[REG_RBP];
 #elif V8_HOST_ARCH_ARM
     sample.pc = mcontext.gregs[R15];
     sample.sp = mcontext.gregs[R13];
     sample.fp = mcontext.gregs[R11];
 #endif

[iposva, 2009/05/08 18:12:35]

As I suggested before this would have been found earlier if you add a

#else
#error Unknown host architecture.

wherever you have a selection of architectures. Overall there should not be too
many of them.

   }
 
   // We always sample the VM state.
   sample.state = Logger::state();
 
   active_sampler_->Tick(&sample);
 }
 
 
 class Sampler::PlatformData : public Malloced {
@@ skipping 55 matching lines @@
   }
 
   // This sampler is no longer the active sampler.
   active_sampler_ = NULL;
   active_ = false;
 }
 
 #endif  // ENABLE_LOGGING_AND_PROFILING
 
 } }  // namespace v8::internal