On 11/21/2014 11:36 AM, Josh Stone wrote:
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.
The findMain logic here is sound, but I want to point out that stripping
chrome is not actually going to help.
Assuming that you don't need the preFork callback, chopping out the
preFork instrumentation should be easy enough; I can send out a patch
(probably late this afternoon or Monday) that implements the change I
discussed in my most recent email if you want a slightly more polished
version that doesn't break preFork wholesale.
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--
--bw
Bill Williams
Paradyn Project
b...@cs.wisc.edu
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