Labels are not (fully) relocated if bound before used

[Zeex]

I was recently upgrading a project of mine to the latest asmjit (previously used the one from Google Code) and made it to the point where everything compiles successfully but there's a problem at runtime, specifically with dword_ptr and labels.

I made a test program to demonstrate it:

bug.cpp:

#include <asmjit/asmjit.h>

#ifdef OLD_ASMJIT
  using namespace AsmJit;
#else
  using namespace asmjit;
  using namespace asmjit::x86;
#endif

int main() {
  #ifdef OLD_ASMJIT
    X86Assembler _;
  #else
    JitRuntime runtime;
    X86Assembler _(&runtime);
  #endif

  Label label = _.newLabel();

  _.mov(eax, 0xdeadbeef);
  _.ret();

  _.bind(label);
  _.mov(eax, 0x11223344);
  _.ret();

  size_t offset = _.getCodeSize();
  _.lea(eax, dword_ptr(label));
  _.jmp(eax);

  void *code = _.make();
  void *func = static_cast<uint8_t*>(code) + offset;

  // Should return 0x11223344
  int ret = asmjit_cast<int(*)()>(func)();

  #ifdef OLD_ASMJIT
    MemoryManager::getGlobal()->free(code);
  #else
    runtime.release(code);
  #endif

  return ret;
}

CMakeLists.txt:

project(bug)
cmake_minimum_required(VERSION 3.0)

option(OLD_ASMJIT TRUE)

add_definitions(-DASMJIT_API=)
if(OLD_ASMJIT)
  add_definitions(-DOLD_ASMJIT)
endif()

set(ASMJIT_STATIC TRUE)

if(OLD_ASMJIT)
  add_subdirectory(asmjit-old/asmjit)
else()
  add_subdirectory(asmjit)
endif()

if(OLD_ASMJIT)
  include_directories(asmjit-old/asmjit/src)
else()
  include_directories(asmjit/src)
endif()

add_executable(bug bug.cpp)
target_link_libraries(bug asmjit)

The program was designed to work with both old and new asmjit. As you can see, it makes a simple function with X86Assembler and then calls it and returns the result.

If you compile it with the old version of asmjit it will jump back to labeland return 0x11223344, as expected. However, with the new (current) version jumps to the start of code and therefore returns 0xdeadbeef.

If it helps, I've done some debugging and found that the offset variable in X86Assembler::_relocCode() is 0 instead of the real offset. I guess that means something is missing in X86Assembler_emit().

Update:

Found a fix, see PR #53.

[kobalicek]

Thanks! Affects 32-bit code generation.

[kobalicek]

Hi Zeex,

I opened another pull related to this, fixing also the second place where the exactly same bug happens.

[kobalicek]

Merged, Closing this one and the original pull. Thanks!