linux-kernel - Re: arch_align_stack() seems useless

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Message-ID: <20070827071413.736e3dcb@laptopd505.fenrus.org>
Date:	Mon, 27 Aug 2007 07:14:13 -0700
From:	Arjan van de Ven <arjan@...radead.org>
To:	Franck Bui-Huu <vagabon.xyz@...il.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: arch_align_stack() seems useless

On Mon, 27 Aug 2007 16:08:31 +0200
Franck Bui-Huu <vagabon.xyz@...il.com> wrote:
> and recently mips do that. Here is the code taken from exec.c which
> calls it:
> 
> 	int setup_arg_pages(struct linux_binprm *bprm,
> 			    unsigned long stack_top,
> 			    int executable_stack)
> 	{
> 		[...]
> 	
> 		stack_top = arch_align_stack(stack_top);
> 		stack_top = PAGE_ALIGN(stack_top);
> 	
> 		[...]
> 	}
> 
> Since PAGE_ALIGN() is called right after arch_align_stack(), it seems
> to me that the call to the latter function is useless...
> 
> Am I missing something ?

arch_align_stack aligns, on x86, within a 2 page range (this is for
cache coloring).  The other thing you missed is that arch_align_stack()
is called in 2 locations, binfmt_elf.c is the primary location for
inside-the-page randomization.
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