Messages in this thread | | | Date | Tue, 26 Jan 2021 13:15:36 +0900 | From | Masami Hiramatsu <> | Subject | Re: [PATCH v3] tracing: precise log info for kretprobe addr err |
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On Mon, 25 Jan 2021 13:38:40 -0500 Steven Rostedt <rostedt@goodmis.org> wrote:
> On Mon, 25 Jan 2021 19:19:27 +0100 > Oleg Nesterov <oleg@redhat.com> wrote: > > > On 01/26, Jianlin Lv wrote: > > > > > > When trying to create kretprobe with the wrong function symbol in tracefs; > > > The error is triggered in the register_trace_kprobe() and recorded as > > > FAIL_REG_PROBE issue, > > > > > > Example: > > > $ cd /sys/kernel/debug/tracing > > > $ echo 'r:myprobe ERROR_SYMBOL_XXX ret=%x0' >> kprobe_events > > > bash: echo: write error: Invalid argument > > > $ cat error_log > > > [142797.347877] trace_kprobe: error: Failed to register probe event > > > Command: r:myprobe ERROR_SYMBOL_XXX ret=%x0 > > > ^ > > > > > > This error can be detected in the parameter parsing stage, the effect of > > > applying this patch is as follows: > > > > > > $ echo 'r:myprobe ERROR_SYMBOL_XXX ret=%x0' >> kprobe_events > > > bash: echo: write error: Invalid argument > > > $ cat error_log > > > [415.89]trace_kprobe: error: Retprobe address must be an function entry > > > Command: r:myprobe ERROR_SYMBOL_XXX ret=%x0 > > > > IOW, the "offset != 0" check removed by this patch is obviously wrong, right? > >
No, not wrong. Even offset != 0, if the symbol exists in the kernel, kprobe_on_func_entry() will check it.
> > Agreed, but... > > > > > --- a/kernel/trace/trace_kprobe.c > > > +++ b/kernel/trace/trace_kprobe.c > > > @@ -830,7 +830,7 @@ static int trace_kprobe_create(int argc, const char *argv[]) > > > flags |= TPARG_FL_RETURN; > > > if (kprobe_on_func_entry(NULL, symbol, offset)) > > > flags |= TPARG_FL_FENTRY; > > > - if (offset && is_return && !(flags & TPARG_FL_FENTRY)) { > > > + if (!strchr(symbol, ':') && is_return && !(flags & TPARG_FL_FENTRY)) { > > > > but why did you add the strchr(':') check instead? > > > > I was really puzzled until I found the this email from Masami: > > https://lore.kernel.org/lkml/20210120131406.5a992c1e434681750a0cd5d4@kernel.org/ > > > > So I leave this to you and Masami, but perhaps you can document this check at > > least in the changelog? > > > > No, you are correct. That needs to be documented in the code.
Agreed. There should be commented that is defered until the module is loaded.
> > I was about to comment that the check requires a comment ;-) > > Jianlin, > > Care to send a v4 of the patch with a comment to why we are checking the > symbol for ':'.
Thank you!
> > Thanks! > > -- Steve >
-- Masami Hiramatsu <mhiramat@kernel.org>
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