linux-kernel - Re: [PATCH 2/5] ftrace: use code patching for ftrace graph tracer

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Date:	Wed, 26 Nov 2008 00:35:53 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Harvey Harrison <harvey.harrison@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	containers@...ts.osdl.org,
	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>,
	"Serge E. Hallyn" <serue@...ibm.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 2/5] ftrace: use code patching for ftrace graph tracer

On Wed, 26 Nov 2008 00:27:04 -0800 Harvey Harrison <harvey.harrison@...il.com> wrote:

> if (code[0] != 0xe9 || old_offset != load32_noalign(&code[1]))
> 
> This is similar to the new API in -mm load_le32_noalign, but I
> don't think it would be worth load_u32_noalign...load32 should
> be enough.
> 
> > > > > +		return -EINVAL;
> > > > > +
> > > > > +	*(int *)(&code[1]) = new_offset;
> > > > 
> > > > Might be able to use put_unaligned_foo() here.
> > > > 
> > > 
> > > 	put_unaligned(new_offset, (int *)(&code[1]));
> > > 
> 
> In a similar vein to above, this becomes:
> 
> 	store32_noalign(&code[1], new_offset);
> 

yes, that's much better than the party tricks with magical sizeof,
which forces you to run around and check the types of everything.

I've seen people doing get_user() on `long' types and such things
occasionally.

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