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Re: [Qemu-devel] [PATCH 3/3] maint: Fix macros with broken 'do/while(0);

From: Michael S. Tsirkin
Subject: Re: [Qemu-devel] [PATCH 3/3] maint: Fix macros with broken 'do/while(0); ' usage
Date: Thu, 30 Nov 2017 16:43:03 +0200

On Thu, Nov 30, 2017 at 07:41:59AM -0600, Eric Blake wrote:
> The point of writing a macro embedded in a 'do { ... } while (0)'
> loop is so that the macro can be used as a drop-in statement with
> the caller supplying the trailing ';'.  Although our coding style
> frowns on brace-less 'if':
>   if (cond)
>     statement;
>   else
>     something else;
> the use of do/while (0) in a macro is absolutely essential for the
> purpose of avoiding a syntax error on the 'else' - but it only works
> if there is no trailing ';' in the macro (as the ';' in the code
> calling the macro would then be a second statement and cause the
> 'else' to not pair to the 'if').

Shouldn't matter if everyone puts the statements in {}, right?

> Many of the places touched in this code are examples of the ugly
> bit-rotting debug print statements; cleaning those up is left as
> a bite-sized task for another day.
> Found mechanically via: $ git grep -B1 'while (0);' | grep -A1 \\\\
> Signed-off-by: Eric Blake <address@hidden>

We can't really rely on code still building for this to do the right
thing, can we?  I did my best to look for uses and I think it's OK, so

Reviewed-by: Michael S. Tsirkin <address@hidden>

but I'm not merging this.

> -- 
> 2.14.3

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