Re: [DynInst_API:] image::findMain fails for -pie

[Josh Stone <jistone@xxxxxxxxxx>]

On 11/21/2014 01:02 AM, Adrian M Negreanu wrote:
> I tried to instrument a strip-ed chrome, as a workaround the
> processCreate issue(s) , only to find another problem, this time in
> image::findMain()

As a workaround, since you're the one stripping it, you can try
stripping slightly less.  Just removing debuginfo with "strip -g" might
be enough to improve your processCreate issues, or use "strip -K main"
to at least keep main in the symbol table, making findMain unnecessary.

> findMain() assumes the entry point address to be an immediate operand:
>  mov    $0x40051b,%rdi
>  callq  0x7ffff7fef3f0
> 
> For chrome, I found this instead
>  lea -0x34f7(%rip),%rdi
>  callq 26f20 <__libc_start_main@plt>
> 
> Josh found the same issue with a strip-ed stap, or as he put it
>  "/usr/bin/stap is PIE, and I removed the debuginfo package"
> 
> Any suggestions for this one ?

I think ideally this should find the call in question, then use the
dataflowAPI to slice back and find the value of %rdi at this point.  I
hope that's smart enough to evaluate things like -0x34f7(%rip), but I
haven't played with it much.  PPC does something similar for r8.

On 32-bit x86, we'll want the last value on the stack instead.