linux-kernel - Re: [PATCH] compiler.h: don't use temporary variable in __compiletime

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <1399973184.4137.8.camel@jlt4.sipsolutions.net>
Date:	Tue, 13 May 2014 11:26:24 +0200
From:	Johannes Berg <johannes@...solutions.net>
To:	James Hogan <james.hogan@...tec.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Daniel Santos <daniel.santos@...ox.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-next <linux-next@...r.kernel.org>,
	linux-metag <linux-metag@...r.kernel.org>
Subject: Re: [PATCH] compiler.h: don't use temporary variable in
 __compiletime_assert()

Hi James,

> Subject: [PATCH] compiler.h: avoid sparse errors in
>  __compiletime_error_fallback()
> 
> Usually, BUG_ON and friends aren't even evaluated in sparse, but
> recently compiletime_assert_atomic_type() was added, and that now
> results in a sparse warning every time it is used.
> 
> The reason turns out to be the temporary variable, after it sparse no
> longer considers the value to be a constant, and results in a warning
> and an error. The error is the more annoying part of this as it
> suppresses any further warnings in the same file, hiding other problems.
> 
> Unfortunately the condition cannot be simply expanded out to avoid the
> temporary variable since it breaks compiletime_assert on old versions of
> GCC such as GCC 4.2.4 which the latest metag compiler is based on.
> 
> Therefore #ifndef __CHECKER__ out the __compiletime_error_fallback which
> uses the potentially negative size array to trigger a conditional
> compiler error, so that sparse doesn't see it.
> 
> Signed-off-by: James Hogan <james.hogan@...tec.com>
> Cc: Johannes Berg <johannes.berg@...el.com>
> Cc: Daniel Santos <daniel.santos@...ox.com>
> Cc: Luciano Coelho <luciano.coelho@...el.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>

Acked-by: Johannes Berg <johannes@...solutions.net>

> It's not particularly pretty, if you can think of a better solution that
> doesn't break old GCC I'm all ears.

>  #ifndef __compiletime_error
>  # define __compiletime_error(message)
> -# define __compiletime_error_fallback(condition) \
> +/*
> + * Sparse complains of variable sized arrays due to the temporary variable in
> + * __compiletime_assert. Unfortunately we can't just expand it out to make
> + * sparse see a constant array size without breaking compiletime_assert on old
> + * versions of GCC (e.g. 4.2.4), so hide the array from sparse altogether.
> + */
> +# ifndef __CHECKER__
> +#  define __compiletime_error_fallback(condition) \
>  	do { ((void)sizeof(char[1 - 2 * condition])); } while (0)
> -#else
> +# endif
> +#endif
> +#ifndef __compiletime_error_fallback
>  # define __compiletime_error_fallback(condition) do { } while (0)
>  #endif


That's pretty much what I had in mind, I may have expressed it a bit
differently but the end result is the same.

Thanks,
johannes

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/