linux-kernel - Re: [PATCH RESEND v3 09/24] ptrace: cleanup arch

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Date:	Sat, 02 Oct 2010 06:13:13 +0000
From:	"Daniel K." <dk@...no>
To:	Namhyung Kim <namhyung@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Roland McGrath <roland@...hat.com>,
	Oleg Nesterov <oleg@...hat.com>, linux-kernel@...r.kernel.org,
	David Howells <dhowells@...hat.com>
Subject: Re: [PATCH RESEND v3 09/24] ptrace: cleanup arch_ptrace() on frv

Namhyung Kim wrote:
> 2010-10-02 (토), 12:57 +0900, Namhyung Kim:
>> 2010-10-02 (토), 03:18 +0000, Daniel K.:
>>> Namhyung Kim wrote:
>>>>       case PTRACE_POKEUSR: /* write the word at location addr in the USER area */
>>>>             ret = -EIO;
>>> -             if ((addr & 3) || addr < 0)
>>> +             if (addr & 3)
>>>                     break;
>>>
>>>> -		ret = 0;
>>>> -		switch (addr >> 2) {
>>>> +		switch (regno) {
>>>>  		case 0 ... PT__END - 1:
>>>> -			ret = put_reg(child, addr >> 2, data);
>>>> -			break;
>>>> -
>>>> -		default:
>>>> -			ret = -EIO;
>>>> +			ret = put_reg(child, regno, data);
>>>>  			break;
>>>>  		}
>>>>  		break;
>>> With this, you remove the default case, and no longer return -EIO in the
>>> cases of PT__END + n, as in the PTRACE_PEEKUSR section above.
>>>
>>> This is a change of behaviour as far as I can tell, and not just a cleanup.
> 
> It would not be a change of behaviour. Because 'ret' was initialized
> with -EIO and only changed in the switch case. So assignment before
> switch can be removed and then will return -EIO in default case.

You are right, I was thrown by the piles of needless code here.

In fact, the whole switch can now be replaced with:

	if (regno < PT__END)
		ret = put_reg(child, regno, data);

but it is perhaps better to use the switch-style, for symmetry with
the PTRACE_PEEKUSR case directly above it?


Sorry to cause alarm.


Daniel K.
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