linux-kernel - Re: [PATCH] unicore32, exec: remove redundant set_fs(USER

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Date:	Mon, 13 Jun 2011 18:02:59 +0200
From:	Mathias Krause <minipli@...glemail.com>
To:	gxt@...c.pku.edu.cn
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, arnd@...db.de
Subject: Re: [PATCH] unicore32, exec: remove redundant set_fs(USER_DS)

On 13.06.2011, 11:19 Guan Xuetao wrote:
> On Fri, 2011-06-10 at 15:11 +0200, Mathias Krause wrote:
>> The address limit is already set in flush_old_exec() so this
>> set_fs(USER_DS) is redundant.
>> 
>> Signed-off-by: Mathias Krause <minipli@...glemail.com>
>> ---
>> arch/unicore32/include/asm/processor.h |    1 -
>> 1 files changed, 0 insertions(+), 1 deletions(-)
>> 
>> diff --git a/arch/unicore32/include/asm/processor.h b/arch/unicore32/include/asm/processor.h
>> index e11cb07..f0d780a 100644
>> --- a/arch/unicore32/include/asm/processor.h
>> +++ b/arch/unicore32/include/asm/processor.h
>> @@ -53,7 +53,6 @@ struct thread_struct {
>> #define start_thread(regs, pc, sp)					\
>> ({									\
>> 	unsigned long *stack = (unsigned long *)sp;			\
>> -	set_fs(USER_DS);						\
>> 	memset(regs->uregs, 0, sizeof(regs->uregs));			\
>> 	regs->UCreg_asr = USER_MODE;					\
>> 	regs->UCreg_pc = pc & ~1;	/* pc */                        \
> 
> Hi Mathias,
> I searched for the code in flush_old_exec(), but I can't find the code
> you mentioned. Could you make it more clear?

Sorry, this statement is based on a commit post v3.0-rc2. Before dac853a (exec:
delay address limit change until point of no return) it was done in
search_binary_handler(), now it is done in flush_old_exec(). Either way
set_fs(USER_DS) gets called before start_thread() so the call there is
redundant.

> And, if all fs codes (not only elf and aout) have the similar
> implementations,

I've checked that all binary format handler call flush_old_exec() before
start_thread(). So: yes.

> perhaps all arch-specific codes should be manipulated
> in the meanwhile.

That's what this LKML thread is for: https://lkml.org/lkml/2011/6/10/65

Thanks,
Mathias--
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