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References: <20050602013641.GL21597@atomide.com> <200506021030.50585.mail@earthworm.de> <20050602174219.GC21363@atomide.com> <20050603223758.GA2227@elf.ucw.cz> <20050610041706.GC18103@atomide.com> <20050610091515.GH4173@elf.ucw.cz>
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Cc: Tony Lindgren <tony@atomide.com>, Christian Hesse <mail@earthworm.de>,
       linux-kernel@vger.kernel.org
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From: Kyle Moffett <mrmacman_g4@mac.com>
Subject: Re: [PATCH] Dynamic tick for x86 version 050602-2
Date: Sat, 11 Jun 2005 13:59:42 -0400
To: Pavel Machek <pavel@ucw.cz>
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On Jun 10, 2005, at 05:15:15, Pavel Machek wrote:
> Hi!
>>> do {} while (0)
>>>
>>> , else you are preparing trap for someone.
>>>
>>
>> Can you please explain what the difference between these two are?
>> Some compiler version specific thing?
>>
>
> It took me quite some remembering. Problem is that with your macros,
> someone can write
>
>     dyn_tick_reprogram_timer()
>     printk();
>
> [notice missing ; at first line], and still get it compile. If you
> replace {} with do {} while (0), he'll get compile error as he should.

Actually, the real reason is for something like this:

#define myfunc1() {}
#define myfunc2() {}

if (a && b) myfunc1();
else        myfunc2();

This would be translated as:

if (a && b) {};
else        {};

Which would generate a syntax error:
zeus:~ kyle$ gcc -c `y -e .c` -o tmp.o <<'EOF'
 > #define myfunc1() {}
 > #define myfunc2() {}
 > void x() {
 >     int a = 0, b = 1;
 >     if (a && b) myfunc1();
 >     else        myfunc2();
 > }
 > EOF
/tmp/y.c8F08d.c: In function ‘x’:
/tmp/y.c8F08d.c:4: error: parse error before "else"

Cheers,
Kyle Moffett