linux-kernel - RE: [rfc] x86, bts: improve X86_PTRACE

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Date:	Thu, 16 Oct 2008 08:12:52 +0100
From:	"Metzger, Markus T" <markus.t.metzger@...el.com>
To:	"Roland Dreier" <rdreier@...co.com>
Cc:	<linux-kernel@...r.kernel.org>, <mingo@...e.hu>,
	<tglx@...utronix.de>, <markus.t.metzger@...il.com>
Subject: RE: [rfc] x86, bts: improve X86_PTRACE_BTS help text

>-----Original Message-----
>From: Roland Dreier [mailto:rdreier@...co.com] 
>Sent: Donnerstag, 16. Oktober 2008 08:57
>To: Metzger, Markus T

> >  config X86_DS
[...]
> > +	def_bool X86_PTRACE_BTS
> > +	depends on X86_DEBUGCTLMSR
>
>using def_bool here to get this turned on if X86_PTRACE_BTS is set
>doesn't seem scalable to more uses of X86_DS.  I would have 
>thought that
>having X86_PTRACE_BTS select X86_DS would make more sense.

We do plan other users. Perfmon2, for example, will be using it.

I fail to see the difference between the two models.
In one case, new users would need to select X86_DS.
In the other case, new users would need to extend the def_bool clause of
X86_DS.

The documentation recommended to use select carefuly, that's why I
picked the other one.

If people think that select is clearer, I will change it.


> > +	  This adds a ptrace interface to the hardware's branch 
>trace store.
> > +
> > +	  Debuggers may use it to collect an execution trace of 
>the debugged
> > +	  application in order to answer the question 'how did 
>I get here?'.
> > +	  Debuggers may trace user mode as well as kernel mode.
> > +
> > +	  Say Y unless there is no application development on 
>this machine
> > +	  and you want to save a small amount of code size.
>
>This looks much better -- someone like me could read this and make an
>informed decision about the config option.

Good. I will send a patch if there is no more feedback on the select vs.
def_bool topic today.

regards,
markus.
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