linux-kernel - Re: [uClinux-dev] [PATCH] FDPIC: respect PT_GNU_STACK exec markings when creating NOMMU stack

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Date:	Sat, 28 Nov 2009 13:47:26 -0500
From:	Mike Frysinger <vapier.adi@...il.com>
To:	uClinux development list <uclinux-dev@...inux.org>
Cc:	David Howells <dhowells@...hat.com>,
	David McCullough <davidm@...pgear.com>,
	Greg Ungerer <gerg@...inux.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	uclinux-dist-devel@...ckfin.uclinux.org,
	linux-kernel@...r.kernel.org
Subject: Re: [uClinux-dev] [PATCH] FDPIC: respect PT_GNU_STACK exec markings 
	when creating NOMMU stack

On Sat, Nov 28, 2009 at 10:24, Mike Frysinger wrote:
> The current code will load the stack size and markings, but then only use
> the markings in the MMU code path.  The NOMMU code path always passes EXEC
> to the mmap() call.  While this doesn't matter to most people during the
> run of the code, it causes a pointless icache flush when starting every
> FDPIC application and by default, that tends to be 128kB of waste.

for some raw numbers:
with my default FDPIC boot (inetd/syslog/watchdog), we icache flush
18,562,124 bytes.  with this stack fix, we cut off 3,538,944 bytes
(19% shrinkage).
-mike
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