linux-kernel - Re: [PATCH v5 3/14] User Space Breakpoint Assistance Layer

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Message-ID: <20100622054429.GB25989@linux.vnet.ibm.com>
Date:	Tue, 22 Jun 2010 11:14:29 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...e.hu>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Mel Gorman <mel@....ul.ie>,
	Randy Dunlap <rdunlap@...otime.net>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Roland McGrath <roland@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Christoph Hellwig <hch@...radead.org>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Oleg Nesterov <oleg@...hat.com>,
	Mark Wielaard <mjw@...hat.com>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jim Keniston <jkenisto@...ux.vnet.ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 3/14] User Space Breakpoint Assistance Layer

> > +/**
> > + * user_bkpt_write_data - Write @nbytes from @kbuf at @vaddr in @tsk.
> > + * Can be used to write to stack or data VM areas, but not instructions.
> > + * Not exported, but available for use by arch-specific user_bkpt code.
> > + * @tsk: The probed task
> > + * @vaddr: Destination address, in user space.
> > + * @kbuf: Source address, in kernel space to be read.
> 
> I'm curious. Anything prevent this from being called on instructions, or
> is this just "Don't do that?". 
> 

Both, 
copy_to_user doesnt work on writes to text.
And if I am right, copy_to_user isnt preferred while writing to text
pages too.

> > +
> > +	memcpy(vaddr_new, vaddr_old, PAGE_SIZE);
> > +	/* poke the new insn in, ASSUMES we don't cross page boundary */
> > +	vaddr = vaddr & (PAGE_SIZE - 1);
> 
> This should probably be vaddr = vaddr & ~PAGE_MASK;

Okay, I will make the corresponding change.
> 
> 
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