linux-kernel - Re: [PATCH] remove untouched code in kfifo

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Date:	Fri, 19 Oct 2012 10:14:14 +0200
From:	richard -rw- weinberger <richard.weinberger@...il.com>
To:	Richard Yang <weiyang@...ux.vnet.ibm.com>
Cc:	Stefani Seibold <stefani@...bold.net>,
	linux-kernel@...r.kernel.org, jkosina@...e.cz
Subject: Re: [PATCH] remove untouched code in kfifo_in

On Fri, Oct 19, 2012 at 8:18 AM, Richard Yang
<weiyang@...ux.vnet.ibm.com> wrote:
> On Fri, Oct 19, 2012 at 07:23:09AM +0200, Stefani Seibold wrote:
>>
>>Am Freitag, den 19.10.2012, 00:37 +0200 schrieb richard -rw- weinberger:
>>> On Thu, Oct 18, 2012 at 3:59 PM, Wei Yang <weiyang@...ux.vnet.ibm.com> wrote:
>>> > In kfifo_in marco, one piece of code is arounded by if(0). This code in
>>> > introduced by Stefani Seibold <stefani@...bold.net> to suppress a compiler
>>> > warning. This warning is not there with the upgrade of gcc version.
>>> >
>>> > This patch just remove this code.
>>>
>>> Are you sure?
>>> This code fragment looks like a compiler bomb to detect type mismatch to me...
>>>
>>
>>Yes, you are great! That was the reason why i made this peace of code.
>>So don't remove it!
> Thanks for your confirmation.
>
> Hmm, would you give me a hint on how it check the type mismatch?

Here a small hint:
---cut---
struct x {
};
struct y {
};

#define check(a, b) \
({ \
        if (0) { \
                typeof(a) __dummy __attribute__ ((unused)); \
                __dummy = (typeof(b))NULL; \
        } \
})

int main(int argc, char **argv)
{
        struct x _x;
        struct y _y;

        check(&_x, &_x); //okay
        check(&_x, &_y); //will explode with "assignment from
incompatible pointer type"

        return 0;
}

---cut---


-- 
Thanks,
//richard
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