truss status (was: cvs commit: src/sys/dev/lmc if_lmc.h)

[John Baldwin]

On Monday 24 July 2006 08:10, Robert Watson wrote:
> On Mon, 24 Jul 2006, Greg 'groggy' Lehey wrote:
> 
> > On Friday, 21 July 2006 at 13:29:38 +0200, Dag-Erling Smrgrav wrote:
> >> Tom Rhodes <trhodes at FreeBSD.org> writes:
> >>> Wait.  I'm lost.  Isn't truss(1) broken on FreeBSD?
> >>
> >> Depends on your definition of broken.  It kind of works provided you have 
> >> /proc mounted.  Still, there's really not much point in using it; 
ktrace(1) 
> >> is better in almost all respects.
> >
> > truss is good in that it gives immediate output.  I used it recently under 
> > 6.1, and I somehow missed that it was broken.
> 
> A few things are wrong with truss, none that make it completely broken:
> 
> (1) In the past there were a number of reports of problems with race
>      conditions during truss attach/detach.  These reports have entirely
>      disappeared, as far as I can tell, due to process locking fixes, procfs
>      fixes, debugging fixes, etc.  If they still exist, they should be
>      investigated, but up-to-date debugging infomation will be needed.

I think the PHOLD/P_WEXIT stuff in 6.1 might have fixed these.

> (2) truss relies on procfs, which is known to be evil, and as such, doesn't
>      work out of the box since we don't mount procfs out of the box.  
Several
>      people have worked on enhancing ptrace() so that it can be used to
>      implement truss, but no one has finished this work.  I think the 
necessary
>      ptrace() traps now exist for system calls so that this could be done.

Well, the biggest thing I found when doing the PHOLD/P_WEXIT stuff that was 
missing was PIOCWAIT and PIOCCONT (IIRC).  Specifically, we don't currently 
have any ptrace() equivalent to that.

-- 
John Baldwin