linux-kernel - Re: Really good idea to allow mmap(0, FIXED)?

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Date:	Fri, 06 Oct 2006 13:20:05 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	Mikael Pettersson <mikpe@...uu.se>
Cc:	David Wagner <daw-usenet@...erner.cs.berkeley.edu>,
	linux-kernel@...r.kernel.org
Subject: Re: Really good idea to allow mmap(0, FIXED)?

On Fri, 2006-10-06 at 12:36 +0200, Mikael Pettersson wrote:
> Arjan van de Ven writes:
>  > >     mmap(0, 4096, PROT_READ|PROT_EXEC|PROT_WRITE,
>  > >         MAP_FIXED|MAP_PRIVATE|MAP_ANONYMOUS, 0, 0);
>  > >     struct s *bar = 0;
>  > 
>  > the question isn't if it's a good idea to allow mmap(0) but to allow
>  > mmap PROT_WRITE | PROT_EXEC !
> 
> It is if you want JITs, code loaders, virtualisation engines, etc
> to continue working.

yeah I know we can't forbid it point blank
(having said that, on architectures where I and D cache aren't coherent
(and there are many, including ia64), most of these are buggy anyway;
the sane ones actually do an mprotect between writing and executing, so
that the kernel can take care of the cache coherency properly)

-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com

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