Messages in this thread | | | Subject | Re: [PATCH v3 3/3] perf probe: Show better error message when failed to find variable | From | He Kuang <> | Date | Mon, 11 May 2015 18:15:37 +0800 |
| |
On 2015/5/11 17:50, Ingo Molnar wrote: > * He Kuang <hekuang@huawei.com> wrote: > >> Hi, Ingo >> >> On 2015/5/11 17:30, Ingo Molnar wrote: >>> * He Kuang <hekuang@huawei.com> wrote: >>> >>>> Indicate to check variable location range in error message when we got >>>> failed to find the variable. >>>> >>>> Before this patch: >>>> >>>> $ perf probe --add 'generic_perform_write+118 bytes' >>>> Failed to find the location of bytes at this address. >>>> Perhaps, it has been optimized out. >>>> Error: Failed to add events. >>>> >>>> After this patch: >>>> $ perf probe --add 'generic_perform_write+118 bytes' >>>> Failed to find the location of bytes at this address. >>> What does this sentence mean? I thought 'address' means 'location of >>> bytes'. So the address identifies the location and obviously we know >>> that. So this message wants to say something else. >> 'generic_perform_write' is a function name, while 'bytes' is a local >> variable in this function. Maybe the variable I chose make you confused. >> >> This maybe clear: >> Failed to find the location of 'bytes' at this address. > Yeah, absolutely! This highlights the importance of putting > user-supplied symbols into quotes and such. > > Maybe even write: > > Failed to find the location of the 'bytes' variable at this address. > > Another question: what does 'generic_perform_write+118' mean here? Why > the offset?
This is for setting a kprobe at the location has an offset of 118 bytes to the entry of the function 'generic_perform_write'.
In the previous patch: https://lkml.org/lkml/2015/5/11/170, we show a valid byte offset range of variables in scope, 118 is an invalid address which can be read from the result, this offset is just for showing the error message.
> > Thanks, > > Ingo > -- > 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/ >
| |