Messages in this thread | | | Date | Wed, 14 Nov 2007 13:27:41 +0530 | From | Srinivasa Ds <> | Subject | Re: [PATCH][RFC] kprobes: Add user entry-handler in kretprobes |
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Abhishek Sagar wrote: > On Nov 13, 2007 12:09 AM, Abhishek Sagar <sagar.abhishek@gmail.com> wrote: >> Whoops...sry for the repeated email..emailer trouble. > > Expecting this one to makes it to the list. Summary again: > > This patch introduces a provision to specify a user-defined callback > to run at function entry to complement the return handler in > kretprobes. Currently, whenever a kretprobe is registered, a user can > specify a callback (return-handler) to be run each time the target > function returns. This is also not guaranteed and is limited by the > number of concurrently pending return instances of the target function > in the current process's context. > > This patch will now allow registration of another user defined handler > which is guaranteed to run each time the current return instance is > allocated and the return handler is set-up. Conversely, if the > entry-handler returns an error, it'll cause the current return > instance to be dropped and the return handler will also not run. The > purpose is to provide flexibility to do certain kinds of function > level profiling using kretprobes. By being able to register function > entry and return handlers, kretprobes will now be able to reduce an > extra probe registration (and associated race) for scenarios where an > entry handler is required to capture the function call/entry event > along with the corresponding function exit event. >
If I understand your intentions(to capture information on function call/entry and corresponding function exit) cleary, I have few concerns on this.
1) How do you map the entry_handler(which gets executed when a process enters the function) with each instance of return probe handler. I accept that entry_handler() will execute each time process enters the function, but to calculate time, one needs to know corresponding instance of return probe handler(there should be a map for each return handler).
Let me explain briefly. Suppose in a SMP system, 4 processes enter the same function at almost sametime(by executing entry_hanlder()) and returns from 4 different locations by executing the return handler. Now how do I match entry_handler() with corresponding instance of return handler for calculating time.
Sometime back, Even I was interested in calculating the function execution time, but I used approach a) .
Now What I think is, there could be 2 solutions to these problem.
a) Collect the entry time and exit time and put it in that kretprobe_instance structure and fetch it before freeing that instance.
b) Or pass ri(kretprobe_instance address to entry_handler) and match it with return probe handler. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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