Re: DTrace panic while probing syscall::open (and possibly many others)

On May 18, 2009, at 06:11 PM, Wesley Shields wrote:

> On Wed, May 13, 2009 at 03:19:05PM +0200, Thomas Backman wrote:
>> OK, so I first posted a thread on the forums about this in 7.2- 
>> RELEASE:
>> http://forums.freebsd.org/showthread.php?t=3834
>> Then filed a PR, kern/134408:
>> http://www.freebsd.org/cgi/query-pr.cgi?pr=134408
>>
>> The very same bug remains in 8-CURRENT/amd64 as of May 13, ~10(am)
>> GMT+2.
>>
>> Steps to reproduce:
>> 1) Build DTrace capable kernel (I followed the wiki DTrace  
>> instructions)
>> 2) Reboot; kldload dtraceall
>> 3) dtrace -n 'syscall::open:entry { self->path = arg0; }
>> syscall::open:return { printf("%s\n", copyinstr(self->path)); }'
>> 4) Crash.
>>
>> Backtrace:
>> [...]
>
> It's not the probe that is the problem. I suspect it's the copyinstr.
>
>> Same panic on two computers (a "real" one, A64 3200+, nForce4, 2GB  
>> RAM;
>> and a Macbook Pro C2D running VMware Fusion). Same panic in 7.2 and  
>> 8.0.
>
> I can easily reproduce this also.
>
> -- WXS

Yup, it's copyinstr() crashing. It works if you simply replace  
printf(...) with printf("file opened\n") which doesn't copy anything  
in, and the backtrace seems (even to me ;) to point towards it.

Regards,
Thomas