linux-kernel - Re: [PATCH] tracing: Cleanup the convoluted softirq tracepoints

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: <20101020015227.GA2011@redhat.com>
Date:	Tue, 19 Oct 2010 21:52:27 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Koki Sanagi <sanagi.koki@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Frederic Weisbecker <fweisbec@...il.com>,
	nhorman@...driver.com, scott.a.mcmillan@...el.com,
	laijs@...fujitsu.com, "H. Peter Anvin" <hpa@...or.com>,
	LKML <linux-kernel@...r.kernel.org>, eric.dumazet@...il.com,
	kaneshige.kenji@...fujitsu.com, David Miller <davem@...emloft.net>,
	izumi.taku@...fujitsu.com, kosaki.motohiro@...fujitsu.com,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	"Luck, Tony" <tony.luck@...el.com>
Subject: Re: [PATCH] tracing: Cleanup the convoluted softirq tracepoints

On Tue, Oct 19, 2010 at 09:36:30PM -0400, Steven Rostedt wrote:
> 
> On Wed, 2010-10-20 at 00:17 +0200, Thomas Gleixner wrote:
> > On Tue, 19 Oct 2010, Thomas Gleixner wrote:
> > > On Tue, 19 Oct 2010, Jason Baron wrote:
> > > > > Now even worse, when you NOP out the jmpq then your tracepoint is
> > > > > still not enabled. Brilliant !
> > > > > 
> > > > 
> > > > The 'jmpq' in the enabled case is patched with a jmpq to the body of the
> > > > tracepoint itself.
> > > 
> > > Brilliant.
> > 
> > IOW, We now jump around the jump which jumps around the disabled code.
> > 
> 
> 
> Do you happen to have CONFIG_CC_OPTIMIZE_FOR_SIZE set? If so, then this
> is a known issue. We even originally had jump label enabled _only_ if
> CC_OPTIMIZE_FOR_SIZE was not set, but hpa NAK'd it.
> 
> http://lkml.org/lkml/2010/9/22/482
> 
> http://lkml.org/lkml/2010/9/20/488
> 
> http://lkml.org/lkml/2010/9/24/259
> 
> -- Steve

thanks Steve. I was about to say this. When CONFIG_CC_OPTIMIZE_FOR_SIZE
is not set we don't get the double 'jmp' and the tracepoint code is
moved out of line. It was mentioned that a number of distros ship with
CONFIG_CC_OPTIMIZE_FOR_SIZE not set, and as Steve mentioned my original
patch set was conditional on !CONFIG_CC_OPTIMIZE_FOR_SIZE.

using hot/cold labels gcc can fix the CONFIG_CC_OPTIMIZE_FOR_SIZE case,
but its a non-trivial amount of work for gcc. I was hoping that if jump
labels are included, we could make the gcc work happen.

thanks,

-Jason
--
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/