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?

Stefan