Re: [Qemu-devel] [PATCH 0/6] hypertrace: Lightweight guest-to-QEMU trace channel

From: "Lluís Vilanova" <vilanova@ac.upc.edu>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Stefan Hajnoczi <stefanha@gmail.com>,
	qemu-devel@nongnu.org, Steven Rostedt <rostedt@goodmis.org>,
	Luiz Capitulino <lcapitulino@redhat.com>,
	lttng-dev@lists.lttng.org, Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [Qemu-devel] [PATCH 0/6] hypertrace: Lightweight guest-to-QEMU trace channel
Date: Tue, 13 Sep 2016 18:50:01 +0200	[thread overview]
Message-ID: <8737l3n3ra.fsf__31625.3387755298$1473785421$gmane$org@fimbulvetr.bsc.es> (raw)
In-Reply-To: <20160913135250.GA4024@stefanha-x1.localdomain> (Stefan Hajnoczi's message of "Tue, 13 Sep 2016 14:52:50 +0100")

Stefan Hajnoczi writes:

> On Mon, Sep 05, 2016 at 04:37:01PM +0200, Lluís Vilanova wrote:
>> I suppose that if you execute the stap script I pasted it will show the proper
>> values. Then it's definitely a problem with Debian's userspace probes.

> Sorry for the delay.  SystemTap static probes appear to work correctly on
> Fedora 24.

> I built qemu.git/master from source with "--enable-trace-backends=dtrace" and
> tried the following:

> $ rpm -qi systemtap kernel-devel | grep Source
> Source RPM  : systemtap-3.0-3.fc24.src.rpm
> Source RPM  : kernel-4.7.2-201.fc24.src.rpm

> (By the way, I hit the same mutex_lock() vs inode_lock() issue in systemtap as you.)

> $ cat test.stp
> probe begin {
> 	printf("hello\n");
> }

> probe process("path/to/qemu-system-x86_64").mark("kvm_ioctl")
> {
> 	printf("%x %p\n", $arg1, $arg2)
> }

> $ sudo stap test.stp -c 'path/to/qemu-system-x86_64 -enable-kvm -m 1024'
> hello
> ae00 0x0
> ae03 0xa
> ae03 0x9
> ae03 0x42
> ae01 0x0

> These are valid argument values.  What happens on your Debian box?

Like in my example, I get all zeroes. So I'll open a bug on debian and assume my
example stap script shows the proper values.

Thanks,
  Lluis
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