* Break on syscall?
@ 2006-05-19 10:59 Alex Bennee
2006-05-19 13:43 ` Daniel Jacobowitz
0 siblings, 1 reply; 6+ messages in thread
From: Alex Bennee @ 2006-05-19 10:59 UTC (permalink / raw)
To: gdb
Is it possible to get gdb to break on entering/exiting a syscall (rather
than breaking on entering libc or some such)? Does gdb use ptrace() to
control breakpoints in the debugged code?
--
Alex, homepage: http://www.bennee.com/~alex/
Famous, adj.: Conspicuously miserable. -- Ambrose Bierce
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Break on syscall?
2006-05-19 10:59 Break on syscall? Alex Bennee
@ 2006-05-19 13:43 ` Daniel Jacobowitz
2006-05-19 22:06 ` Mark Kettenis
0 siblings, 1 reply; 6+ messages in thread
From: Daniel Jacobowitz @ 2006-05-19 13:43 UTC (permalink / raw)
To: Alex Bennee; +Cc: gdb
On Fri, May 19, 2006 at 11:15:30AM +0100, Alex Bennee wrote:
> Is it possible to get gdb to break on entering/exiting a syscall (rather
> than breaking on entering libc or some such)?
This is not supported.
> Does gdb use ptrace() to
> control breakpoints in the debugged code?
Breakpoints are inserted usually using PTRACE_POKETEXT.
--
Daniel Jacobowitz
CodeSourcery
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Break on syscall?
2006-05-19 13:43 ` Daniel Jacobowitz
@ 2006-05-19 22:06 ` Mark Kettenis
2006-05-19 23:13 ` Daniel Jacobowitz
0 siblings, 1 reply; 6+ messages in thread
From: Mark Kettenis @ 2006-05-19 22:06 UTC (permalink / raw)
To: drow; +Cc: kernel-hacker, gdb
> Date: Fri, 19 May 2006 08:48:35 -0400
> From: Daniel Jacobowitz <drow@false.org>
>
> On Fri, May 19, 2006 at 11:15:30AM +0100, Alex Bennee wrote:
> > Is it possible to get gdb to break on entering/exiting a syscall (rather
> > than breaking on entering libc or some such)?
>
> This is not supported.
But I think it would be nice if we would support something like "catch
syscall", just like we support "catch fork".
Mark
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Break on syscall?
2006-05-19 22:06 ` Mark Kettenis
@ 2006-05-19 23:13 ` Daniel Jacobowitz
2006-05-20 3:00 ` PAUL GILLIAM
0 siblings, 1 reply; 6+ messages in thread
From: Daniel Jacobowitz @ 2006-05-19 23:13 UTC (permalink / raw)
To: Mark Kettenis; +Cc: kernel-hacker, gdb
On Fri, May 19, 2006 at 11:16:15PM +0200, Mark Kettenis wrote:
> > Date: Fri, 19 May 2006 08:48:35 -0400
> > From: Daniel Jacobowitz <drow@false.org>
> >
> > On Fri, May 19, 2006 at 11:15:30AM +0100, Alex Bennee wrote:
> > > Is it possible to get gdb to break on entering/exiting a syscall (rather
> > > than breaking on entering libc or some such)?
> >
> > This is not supported.
>
> But I think it would be nice if we would support something like "catch
> syscall", just like we support "catch fork".
Yes, probably. I think I even started work on this once. It's just a
bit trickier. Not only do you want to be able to decode arguments, but
there are other problems... for example, I think procfs allows it, but
traditionally ptrace has no way to request a single step and stop if
entering a syscall, so you'd need an arch hook to detect it to handle
that case.
A nice project for some rainy month :-)
--
Daniel Jacobowitz
CodeSourcery
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Break on syscall?
2006-05-19 23:13 ` Daniel Jacobowitz
@ 2006-05-20 3:00 ` PAUL GILLIAM
2006-05-21 13:25 ` Daniel Jacobowitz
0 siblings, 1 reply; 6+ messages in thread
From: PAUL GILLIAM @ 2006-05-20 3:00 UTC (permalink / raw)
To: Daniel Jacobowitz; +Cc: Mark Kettenis, kernel-hacker, gdb
On Fri, 2006-05-19 at 18:05 -0400, Daniel Jacobowitz wrote:
> On Fri, May 19, 2006 at 11:16:15PM +0200, Mark Kettenis wrote:
> > > Date: Fri, 19 May 2006 08:48:35 -0400
> > > From: Daniel Jacobowitz <drow@false.org>
> > >
> > > On Fri, May 19, 2006 at 11:15:30AM +0100, Alex Bennee wrote:
> > > > Is it possible to get gdb to break on entering/exiting a syscall (rather
> > > > than breaking on entering libc or some such)?
> > >
> > > This is not supported.
> >
> > But I think it would be nice if we would support something like "catch
> > syscall", just like we support "catch fork".
>
> Yes, probably. I think I even started work on this once. It's just a
> bit trickier. Not only do you want to be able to decode arguments, but
> there are other problems... for example, I think procfs allows it, but
> traditionally ptrace has no way to request a single step and stop if
> entering a syscall, so you'd need an arch hook to detect it to handle
> that case.
>
> A nice project for some rainy month :-)
>
From the ptrace(2) man page on Linux:
PTRACE_SYSCALL, PTRACE_SINGLESTEP
Restarts the stopped child as for PTRACE_CONT, but arranges for
the child to be stopped at the next entry to or exit from a sys-
tem call, or after execution of a single instruction, respec-
tively. (The child will also, as usual, be stopped upon receipt
of a signal.) From the parent’s perspective, the child will
appear to have been stopped by receipt of a SIGTRAP. So, for
PTRACE_SYSCALL, for example, the idea is to inspect the argu-
ments to the system call at the first stop, then do another
PTRACE_SYSCALL and inspect the return value of the system call
at the second stop. (addr is ignored.)
The 'ltrace' utility uses this to trace system calls. It uses a sleazy
table (/etc/ltrace.cfg) to find out about their arguments... GDB should
be able to do a much better job, although matching syscall numbers to
their associated library routines would be a challenge (at least for me
8-)
-=# Paul #=-
PS: Here in Oregon, rainy months are the norm 8-)
^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: Break on syscall?
2006-05-20 3:00 ` PAUL GILLIAM
@ 2006-05-21 13:25 ` Daniel Jacobowitz
0 siblings, 0 replies; 6+ messages in thread
From: Daniel Jacobowitz @ 2006-05-21 13:25 UTC (permalink / raw)
To: PAUL GILLIAM; +Cc: Mark Kettenis, kernel-hacker, gdb
On Fri, May 19, 2006 at 03:09:31PM -0700, PAUL GILLIAM wrote:
> > traditionally ptrace has no way to request a single step and stop if
> > entering a syscall, so you'd need an arch hook to detect it to handle
> > that case.
> From the ptrace(2) man page on Linux:
>
> PTRACE_SYSCALL, PTRACE_SINGLESTEP
That doesn't conflict with what I said. You can't issue PTRACE_SYSCALL
and PTRACE_SINGLESTEP at the same time.
> The 'ltrace' utility uses this to trace system calls. It uses a sleazy
> table (/etc/ltrace.cfg) to find out about their arguments... GDB should
> be able to do a much better job, although matching syscall numbers to
> their associated library routines would be a challenge (at least for me
> 8-)
GDB can do vastly better, but it's not a small project.
--
Daniel Jacobowitz
CodeSourcery
^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2006-05-20 0:18 UTC | newest]
Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2006-05-19 10:59 Break on syscall? Alex Bennee
2006-05-19 13:43 ` Daniel Jacobowitz
2006-05-19 22:06 ` Mark Kettenis
2006-05-19 23:13 ` Daniel Jacobowitz
2006-05-20 3:00 ` PAUL GILLIAM
2006-05-21 13:25 ` Daniel Jacobowitz
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox