Re: [DynInst_API:] Snippet register get modified by EmitStackAlign

[Bill Williams <bill@xxxxxxxxxxx>]

On 01/15/2015 08:07 AM, Xi Chen wrote:
> Hi,
>    I got a situation that Dyninst overwrite register value which
> generate in my snippet because of the protection of stack and eflag
> register.  Because in the emitStackAlign function (emit-x86.C), it try
> to align the stack and rax register is used in the middle. so if the
> snippet which put result into $rax, the value will be modified.
>    A generated example:
>   lea    -0x80(%rsp),%rsp
>   push   %rax
>   lahf
>   seto   %al
>   push   %rax
>   mov    0x655df0,%rax --> the snippet I added.
>   pop    %rax
>   add    $0x7f,%al
>   sahf
>   pop    %rax
>   lea    0x80(%rsp),%rsp
>
> I want to ask if there are any API which I can turn off this trampline code?
> Thanks in advance.
This is one of the problems with inserting raw assembly snippets; 
Dyninst's instrumentation contract specifies that instrumentation may 
not modify the original program in an unspecified way. There are methods 
available to do this; for instance, you can modify original program 
variables, or you can modify original registers (in their appropriately 
saved locations) with registerExprs (though this is obviously not 
portable, and often not recommended).
Can you tell us a bit about the actual problem you're trying to solve? 
You're putting in a great deal of effort to try to force Dyninst to do 
things in a particular way, and there's often an easier way to 
accomplish a particular goal.
> --
> Best Regards
> X.Chen
>
>
>
>
> _______________________________________________
> Dyninst-api mailing list
> Dyninst-api@xxxxxxxxxxx
> https://lists.cs.wisc.edu/mailman/listinfo/dyninst-api

--
--bw

Bill Williams
Paradyn Project
bill@xxxxxxxxxxx