From: Dave Voutila <dv@sisu.io>
Subject: Re: btrace: Parse unset arguments to 0
To: Christian Ludwig <christian_ludwig@genua.de>
Cc: "tech@openbsd.org" <tech@openbsd.org>
Date: Tue, 16 Jan 2024 07:38:19 -0500


Christian Ludwig <christian_ludwig@genua.de> writes:

> [[S/MIME Signed Part:Undecided]]
> Hi,
>
> On Sun, 2024-01-14 at 22:04 -0500, Dave Voutila wrote:
>> Do you have a simple btrace example? I believe there's an issue here,
>> but not sure I'm following how to trigger it.
>
> Use an undefined argument in any probe.
>
> A simple reproducer would be:
>
> $ doas btrace -e 'tracepoint:sched:on__cpu { printf("%s\n", arg0); }'
> Segmentation fault (core dumped)
>

tracepoint:sched:on_cpu doesn't provide any args. If you change the
probe filter to of_cpu and use arg9 it doesn't segfault.

I'll look at this a little more closely this week. I'd like to
understand the behavior before we start patching the string function
logic.

-dv