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Date: Sun, 5 Sep 2010 20:57:35 +0300
From: "Michael S. Tsirkin" <mst@redhat.com>
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Subject: [Qemu-devel] Re: [PATCH 08/15] blkdebug: fix enum comparison
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To: Blue Swirl <blauwirbel@gmail.com>
Cc: qemu-devel <qemu-devel@nongnu.org>

On Sun, Sep 05, 2010 at 03:06:32PM +0000, Blue Swirl wrote:
> The signedness of enum types depend on the compiler implementation.
> Therefore the check for negative values may or may not be meaningful.
> 
> Fix by explicitly casting to a signed integer.
> 
> Since the values are also checked earlier against event_names
> table, this is an internal error. Change the 'if' to 'assert'.
> 
> This also fixes a warning with GCC flag -Wtype-limits.
> 
> Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
> ---
>  block/blkdebug.c |    4 +---
>  1 files changed, 1 insertions(+), 3 deletions(-)
> 
> diff --git a/block/blkdebug.c b/block/blkdebug.c
> index 2a63df9..4d6ff0a 100644
> --- a/block/blkdebug.c
> +++ b/block/blkdebug.c
> @@ -439,9 +439,7 @@ static void blkdebug_debug_event(BlockDriverState
> *bs, BlkDebugEvent event)
>      struct BlkdebugRule *rule;
>      BlkdebugVars old_vars = s->vars;
> 
> -    if (event < 0 || event >= BLKDBG_EVENT_MAX) {
> -        return;
> -    }
> +    assert((int)event >= 0 && event < BLKDBG_EVENT_MAX);

I am not sure all compilers must generate a negative value from
a very large unsigned integer cast to int.

assert((unsigned)event < BLKDBG_EVENT_MAX);

will do the same but without integer overflow.

> 
>      QLIST_FOREACH(rule, &s->rules[event], next) {
>          process_rule(bs, rule, &old_vars);
> -- 
> 1.6.2.4