linux-kernel - Re: [patch 2/3] MAP_NOZERO

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Message-ID: <a36005b50706262045g79c4accak21fea740fdc1bffd@mail.gmail.com>
Date:	Tue, 26 Jun 2007 20:45:28 -0700
From:	"Ulrich Drepper" <drepper@...il.com>
To:	"Rik van Riel" <riel@...hat.com>
Cc:	"Davide Libenzi" <davidel@...ilserver.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>
Subject: Re: [patch 2/3] MAP_NOZERO - implement sys_brk2()

On 6/26/07, Rik van Riel <riel@...hat.com> wrote:
> Since programs can get back free()d memory after a malloc(),
> with the old contents of the memory intact, surely your
> MAP_NONZERO behavior could be the default for programs that
> can get away with it?
>
> Maybe we could use some magic ELF header, similar to the
> way non-executable stack is handled?

No.  This is an implementation detail of the libc version.  The malloc
as compiled today is expecting brk-ed memory to be zeroed.  This
default can of course be changed (it's a simple define) but you cannot
make this the default behavior for brk.
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