linux-kernel - Re: [PATCH 0/3] tracepoints: delay argument evaluation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.00.0905191826031.7816@gandalf.stny.rr.com>
Date:	Tue, 19 May 2009 18:36:56 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
cc:	Jason Baron <jbaron@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>, jiayingz@...gle.com,
	mbligh@...gle.com, roland@...hat.com,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 0/3] tracepoints: delay argument evaluation


[ added Christoph ]

On Tue, 19 May 2009, Mathieu Desnoyers wrote:

> * Jason Baron (jbaron@...hat.com) wrote:
> > hi,
> > 
> > After disassembling some of the tracepoints, I've noticed that arguments that
> > are passed as macros or that perform  dereferences, evaluate prior to the
> > tracepoint on/off check. This means that we are needlessly impacting the 
> > off case.
> > 
> > I am proposing to fix this by adding a macro that first checks for on/off and
> > then calls 'trace_##name', preserving type checking. Thus, callsites have to 
> > move from:
> > 
> > trace_block_bio_complete(md->queue, bio);
> > 
> > to:
> > 
> > tracepoint_call(block_bio_complete,  md->queue, bio);
> > 
> 
> I knew this limitation in the first place, but decided it was not worth
> uglifying the tracepoint call site for it.
> 
> The expected use is to pass a pointer or a value as tracepoint argument
> and dereference it in the callback attached to it.
> 
> Is there any _real_ added value for going through this API change pain ?
> 

I agree with Mathieu that I don't think we want to "uglify" the callers. 
But I also agree with Jason that we must not add any overhead to the "off" 
state when we can avoid it.

If it comes down to the two, I would lean towards the "uglify" if it shows 
performance benefits in the "off" case.

Perhaps I'll try to see if I can fool CPP to getting both worlds. But this 
will be tricky :-/

When are we going to get our own C pre-processor?

-- Steve

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/