ptrace Issues

ptrace Issues

[Udo A. Steinberg]

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Hi all,

I have discovered that recently I can no longer attach via strace to 
already running processes for a long time. Specifically I have a daemon which
sleeps in select and periodically wakes up from SIGALRM signals. As soon as a
signal hits, strace quits on 2.5.69, however, it works fine on 2.4.21-rc.
Can someone shed some light on what's going on?

root@Corona:~> strace -p 527
--- SIGSTOP (Stopped (signal)) ---
--- SIGSTOP (Stopped (signal)) ---
select(7, [0 3 6], [], NULL, NULL)      = ? ERESTARTNOHAND (To be restarted)
--- SIGALRM (Alarm clock) ---
root@Corona:~> echo $?
0

-Udo.

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Re: ptrace Issues

[Daniel Jacobowitz]

On Fri, May 09, 2003 at 12:47:59AM +0200, Udo A. Steinberg wrote:
> 
> Hi all,
> 
> I have discovered that recently I can no longer attach via strace to 
> already running processes for a long time. Specifically I have a daemon which
> sleeps in select and periodically wakes up from SIGALRM signals. As soon as a
> signal hits, strace quits on 2.5.69, however, it works fine on 2.4.21-rc.
> Can someone shed some light on what's going on?

Sorry it took so long...

> root@Corona:~> strace -p 527
> --- SIGSTOP (Stopped (signal)) ---
> --- SIGSTOP (Stopped (signal)) ---
> select(7, [0 3 6], [], NULL, NULL)      = ? ERESTARTNOHAND (To be restarted)
> --- SIGALRM (Alarm clock) ---
> root@Corona:~> echo $?
> 0

I can't explain why it works for you on 2.4.21-rc.  Were they the same
system and strace version?

The short answer appears to be: this is a bug in strace, not a bug in
the kernel.  If you get 4.4.98, it'll work.  There was an off-by-one
bug in parsing /proc/%d/status for the list of signals.

-- 
Daniel Jacobowitz
MontaVista Software                         Debian GNU/Linux Developer