linux-kernel - Re: [RFC PATCH 05/13] list.h: Fix parentheses around macro pointer parameter use

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Message-ID: <ZF4crs8iKBGH3lJe@smile.fi.intel.com>
Date:   Fri, 12 May 2023 14:02:06 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        David Howells <dhowells@...hat.com>,
        Ricardo Martinez <ricardo.martinez@...ux.intel.com>
Subject: Re: [RFC PATCH 05/13] list.h: Fix parentheses around macro pointer
 parameter use

On Mon, May 08, 2023 at 09:46:40AM -0400, Mathieu Desnoyers wrote:
> On 2023-05-08 08:16, Andy Shevchenko wrote:

...

> The only use I found that would break is as follows:
> 
> LIST_HEAD(testlist);
> 
> int f2(void)
> {
>         return 1;
> }
> 
> #define eval(...)       __VA_ARGS__
> 
> void f(void)
> {
>    struct list_head *pos;
> 
>    list_for_each(pos, eval(f2(), &testlist)) {
>            //...
>    }
> }
> 
> Because "eval()" will evaluate "f(), &testlist" with comma and all, without
> enclosing parentheses.
> 
> So the question is: do we want to support this kind-of-odd macro evaluation,
> considering that it requires adding parentheses around pretty much all macro
> parameters when used as expressions between commas?

Similar question can be asked for your initial motivation to support indirect
pointers. I found the double pointer as weird as this macro case. But it can be
only me. Hence I left this to the more experienced developers to express their
opinions.

-- 
With Best Regards,
Andy Shevchenko