how to tweak x86 code generation to instrument certain opcodes with CC trap?

[William Cohen]

On 10/23/2015 11:37 AM, Yasser Shalabi wrote:
> Hey Will,
> 
> Thanks for the quick reply. Yeah I need the int3 instruction to be
> statically included in he binary so I can't use any dynamic
> instrumentation tool.

Dyninst can do binary rewrites of executables so that might still be suitable.

http://www.dyninst.org/sites/default/files/downloads/w2009/legendre-binrewriter.pdf

-Will

> 
> On Fri, Oct 23, 2015 at 10:32 AM, William Cohen <wcohen@redhat.com> wrote:
>> On 10/23/2015 01:37 AM, Yasser Shalabi wrote:
>>> Hello,
>>>
>>> I am new to the GCC code. I want to make a simple modification to the
>>> back end. I want to add a debug exception (int3) to be generated
>>> before any instance of certain x86 instructions.
>>>
>>> I tried to modify gcc/config/i386/i386.md by adding a "int3" to the
>>> define_insn for instructions of interest. But that just caused
>>> configure to fail (cannot run generated C programs).
>>>
>>> Any pointers on how to approach this? Also, suggestions for
>>> alternative approaches are also welcome.
>>>
>>> Thanks!
>>>
>>
>> Hi,
>>
>> Do you need the int3 specifically before those instructions?  Or are you just looking to instrument the code and collect some information before those instructions are executed?  Some alternative instrumentation tools you might look at to instrument existing code are:
>>
>> dyninst http://www.dyninst.org/
>> Valgrind http://valgrind.org/
>> Intel's Pin tool https://software.intel.com/en-us/articles/pin-a-dynamic-binary-instrumentation-tool
>>
>> -Will