From: Adrien Kunysz <adrien@kunysz.be>
To: Josh Stone <jistone@redhat.com>
Cc: contemplating zombie <contemplatingzombie@gmail.com>,
systemtap@sourceware.org
Subject: Re: Puzzling output of stp script
Date: Sun, 25 Dec 2011 20:20:00 -0000 [thread overview]
Message-ID: <20111225110952.GD17069@chouffe> (raw)
In-Reply-To: <4EF6BAEB.7000006@redhat.com>
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On Sat, Dec 24, 2011 at 09:55:55PM -0800, Josh Stone wrote:
> On 12/24/2011 10:31 AM, contemplating zombie wrote:
> > Hi,
> >
> > I am new to systemtap and I was trying out following example script
> > given in the documentation:
> >
> > probe kernel.function("*@net/socket.c") {
> > printf ("%s -> %s\n", thread_indent(1), probefunc())
> > }
> >
> > probe kernel.function("*@net/socket.c").return {
> > printf ("%s <- %s\n", thread_indent(-1), probefunc())
> > }
> >
> > I sshed into a remote machine and executed it. What I see is that the
> > stack frames just keep on growing to right and do not return. Won't
> > that cause a stack overflow eventually?
>
> The reason is that you are probing more functions on entry than you are
> on return. There's no stack issue; the probes are just imbalanced.
>
> There are two flavors of entry probe: .call and .inline. If you don't
> specify, then you get a union of both. However, .return probes only
> work for the .call flavor, because there is no real return from inlined
> functions.
>
> So when you need balanced probes for entering and leaving functions, use
> .call and .return. You could also be clever and represent the .inline
> separately with thread_indent(0).
And that particular example was already fixed a while ago btw:
http://sourceware.org/git/gitweb.cgi?p=systemtap.git;a=commitdiff;h=396afcee5ada2d207b7a6691d4b7ce473e7b2a65
> > 0 sshd(804): -> sock_poll
> > 11 sshd(804): <- sock_poll
> > 0 sshd(804): -> sock_aio_read
> > 2 sshd(804): -> alloc_sock_iocb
> > 3 sshd(804): <- alloc_sock_iocb
> > 5 sshd(804): -> do_sock_read
> > 7 sshd(804): -> __sock_recvmsg
> > 9 sshd(804): -> __sock_recvmsg_nosec
> > 15 sshd(804): <- sock_aio_read
>
> Notice right here, you got a return from sock_aio_read, jumping back
> over three other "calls". I'll bet that do_sock_read, __sock_recvmsg,
> and __sock_recvmsg_nosec were all inlined in your kernel.
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next prev parent reply other threads:[~2011-12-25 11:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CAO_gTC6yXVN-6a-aj6YFy4Z_7wGaMRzbHTWWWdQOyWgD=g0rOQ@mail.gmail.com>
2011-12-24 19:14 ` contemplating zombie
2011-12-24 22:56 ` Adrien Kunysz
2011-12-25 5:56 ` contemplating zombie
2011-12-25 11:07 ` Josh Stone
2011-12-25 20:20 ` Adrien Kunysz [this message]
2011-12-25 23:59 ` Mark Wielaard
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