Re: [DynInst_API:] Do not trace children

[Gerard <nouboh@xxxxxxxxx>]

Hi,

Thanks for your answers. I'll try using a callback.Â

I'm instrumenting a process that at some point compiles a code invoking gccÂtrough the system() function. I have made more tests and I see that the slow down is worse in the first call, does this makes sense?

Those are the times that I observe while I'm instrumenting with dyninst (just the function that wraps the call to system()):

Compilation time 0: 0.984198

Compilation time 1: 0.080625

Compilation time 2: 0.084245

Compilation time 3: 0.077437

Compilation time 4: 0.084535

Compilation time 5: 0.111851

Compilation time 6: 0.087407

Compilation time 7: 0.090078

Compilation time 8: 0.093158

Compilation time 9: 0.075809

While without dyninst the times are between 0.03 ~ 0.04 seconds.

Gerard

2015-01-20 18:37 GMT+01:00 Bill Williams <bill@xxxxxxxxxxx>:

On 01/20/2015 11:22 AM, Matthew LeGendre wrote:

The closest you can get is to register a callback that triggers on fork,
then detach from the child in that callback.

There's not really a faster way to disable tracing of children, as
Dyninst needs to clean its instrumentation from child processes before
detaching.

I'm also somewhat curious what aspect of Dyninst's fork behavior is responsible for the slowdown you're observing, Gerard. Can you tell us a bit about your use case and more details about why/how Dyninst is responsible for this slowdown?

Matt is of course correct that if this is a fork without a subsequent exec, that it's necessary for Dyninst to remove all its instrumentation. In principle, if we knew that all forks would be followed either by an immediate exec or a crash, we could dispense with that instrumentation entirely, but in practice that's not generally a safe assumption.

Another option that may be effective is performing the initial instrumentation with binary rewriting...that should have substantially better behavior for what you want re: fork/exec.

-Matt

On Mon, 19 Jan 2015, Gerard wrote:

Hello,
Is it possible to not trace the children created by a mutatee? I want to
avoid the time penalty introduced by dyninst when a mutatee creates a
children.

Thanks,

Gerard

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--
--bw

Bill Williams
Paradyn Project
bill@xxxxxxxxxxx