Hi, 2012/9/26 Masami Hiramatsu <masami.hiramatsu...@hitachi.com>: > (2012/09/26 11:52), Hyeoncheol Lee wrote: >> Hi, >> >> uprobe_event only supports %REG arguments. I think that memory fetch, >> return value fetch, memory dereference functions in >> kernel/trace/trace_probe.c are good for uprobe_event. So with a little >> modification of parse_probe_arg(), uprobe_event can support @ADDR, >> $retval, offs(FETCHARGS) except @SYM, $stack, $stackN. Is it right? > > Hi Hyeoncheol, > > Perhaps, it is not so small things, but at least, we can try. > In the userspace, memories(pages) can be paged out on swap or > files. In that case, memory dereference function needs to track > down the data on the disk and it causes I/O. This means we will > see the visible performance degradation with tracing. > And also, sometime a pointer value (address) is broken, in that > case we have to ensure the address is actually valid before > accessing it. > > Of cause, without tracking paged-out data, it is easy > to support, because that is already done in kprobe event. > I'm not sure how it is useful, because sometimes it will > fail to access gather the data. > However it is good for the first step, I think.
Yes, we should consider paged-out data. I forgot this. > > Srikar, what would you think? > > BTW, if we can support offs(FETCHARGS), $stack and $stackN > are also available. ;) Yes, but we should check whether the given address is in an user stack or not. and these require CPU architecture dependent codes. > > Thank you, > > -- > Masami HIRAMATSU > Software Platform Research Dept. Linux Technology Center > Hitachi, Ltd., Yokohama Research Laboratory > E-mail: masami.hiramatsu...@hitachi.com > > Thanks for your answer. It is very help to me. ;) Hyeoncheol -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
