linux-kernel - Re: [patch 00/11] Hardware Breakpoint interfaces

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Date:	Wed, 11 Mar 2009 18:30:44 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Roland McGrath <roland@...hat.com>
Subject: Re: [patch 00/11] Hardware Breakpoint interfaces


* K.Prasad <prasad@...ux.vnet.ibm.com> wrote:

> On Wed, Mar 11, 2009 at 12:34:43PM -0400, Alan Stern wrote:
> > On Wed, 11 Mar 2009, K.Prasad wrote:
> > 
> > > The hardware breakpoint interfaces haven't been put under any CONFIG_
> > > till now, but I think we should bring them under a new config, say
> > > CONFIG_HW_BREAKPOINT. It would help create a dependancy for
> > > CONFIG_KSYM_TRACER too.
> > 
> > With these patches, ptrace is dependent on hw-breakpoint.  
> > You can't disable CONFIG_HW_BREAKPOINT without breaking 
> > ptrace.
> > 
> > Alan Stern
> > 
> 
> Agreed. We might have to retain the old code for ptrace and 
> put the new implementation under #ifdef CONFIG_HW_BREAKPOINT 
> to get them working. What do you think?

With the simple reservation mechanism i suggested i have no 
problem with having HW_BREAKPOINT enabled [selected] 
unconditionally on x86.

Your ptrace changes are an improvement in terms of code quality 
so as long as the facility is simple and obvious, it's a step 
forward.

#ifdefs are ugly and hard to maintain - especially in such a
rarely used and still critical API as ptrace.

	Ingo
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