Re: [PATCH v3 0/8] [RfC] fix tracing for modules

[Gerd Hoffmann]

On Fri, Apr 09, 2021 at 02:17:13PM +0100, Daniel P. Berrangé wrote:
> On Fri, Apr 09, 2021 at 03:12:45PM +0200, Gerd Hoffmann wrote:
> >   Hi,
> > 
> > > eg a trace point "dma_map_wait" gets mapped to probes in many
> > > .stp files, once per target, because we need to match based on
> > > the executable path:
> > > 
> > >   probe qemu.system.x86_64.dma_map_wait = 
> > > process("/usr/libexec/qemu-system-x86_64").mark("dma_map_wait")
> > 
> > So, that changes with modules, we need the module name now, i.e.
> > 
> >     probe qemu.system.x86_64.qxl_soft_reset = \
> >     
> > process("/home/kraxel/qemu-install/lib/qemu/hw-display-qxl.so").mark("qxl_soft_reset")
> > 
> > We could repeat that in every qemu-system-$arch.stp file.
> 
> This would have the surprise the 'qemu.system.x86_64.qxl_soft_reset'
> probes will fire even for qemu-system-ppc64 / qemu-system-xxxxx etc
> because we've not restricted the scope as the original probe did.

Oh, right.

> If we can't fix that, then we must use the second option to avoid
> the surprise IMHO

Yep.  Got that working.  Only problem is qemu-trace-stap is broken now
and it seems there is no easy way out.  Right now qemu-trace-stap can
simply work with a constant prefix, with that change the prefix can be
either qemu.system.$arch or qemu.system.modules and I suspect there is
no way around listing tracepoints to figure the correct name ...

take care,
  Gerd

PS: https://git.kraxel.org/cgit/qemu/log/?h=sirius/trace-modules