netdev - Re: [PATCH] net: xfrm_user: use BUG_ON instead of if condition followed by BUG

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Message-ID: <20171025040541.GA1999@gondor.apana.org.au>
Date:   Wed, 25 Oct 2017 12:05:41 +0800
From:   Herbert Xu <herbert@...dor.apana.org.au>
To:     David Miller <davem@...emloft.net>
Cc:     garsilva@...eddedor.com, steffen.klassert@...unet.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: xfrm_user: use BUG_ON instead of if condition
 followed by BUG

On Tue, Oct 24, 2017 at 05:48:42PM +0900, David Miller wrote:
> 
> This discussion has happened before.
> 
> But I'll explain the conclusion here for your benefit.
> 
> BUG_ON() is a statement and everything inside of it will
> always execute.
> 
> BUG_ON() is always preferred because it allows arch
> specific code to pass the conditional result properly
> into inline asm and builtins for optimal code generation.

This is a good point.  However, while a little bit more verbose you
can still achieve the same assembly-level result by something like

	int err;

	err = <insert real code here>;
	BUG_ON(err);

Having real code in BUG_ON may pose problems to people reading the
code because some of us tend to ignore code in BUG_ON and similar
macros such as BUILD_BUG_ON.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt