linux-kernel - Re: [RFC PATCH 01/11] Add basic support for gcc profiler instrumentation

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Message-ID: <20080103181651.GC3627@sequoia.sous-sol.org>
Date:	Thu, 3 Jan 2008 10:16:51 -0800
From:	Chris Wright <chrisw@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...e.hu>, LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	"William L. Irwin" <sparclinux@...r.kernel.org>,
	Steven Rostedt <srostedt@...hat.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org
Subject: Re: [RFC PATCH 01/11] Add basic support for gcc profiler
	instrumentation

* Steven Rostedt (rostedt@...dmis.org) wrote:
> Hmm, I know paravirt-ops had an issue with mcount in the RT tree. I can't
> remember the exact issues, but it did have something to do with the way
> parameters were passed in.
> 
> Chris, do you remember what the issues were?

Yes, paravirt ops have a well-specified calling convention (register
based).  There was a cleanup that Andi did that caused the problem
because it removed all the "fastcall" annotations since -mregparm=3
is now always on for i386.  Since MCOUNT disables REGPARM the calling
convention changes (caller pushes to stack, callee expects register)
chaos ensues.  I sent a patch to fix that quite some months back, but
it went stale and I neglected to update it.  Would you like me to dig
it up refresh and resend?

thanks,
-chris
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