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

[Lluís Vilanova]

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