linux-kernel - Re: typecheck code

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

Message-ID: <AANLkTimTQxDCJ004VOFCdo3rz01tHsj9R4Ce1OGb75sH@mail.gmail.com>
Date:	Mon, 31 Jan 2011 10:03:36 -0800
From:	Manish Katiyar <mkatiyar@...il.com>
To:	Sri Ram Vemulpali <sri.ram.gmu06@...il.com>
Cc:	Kernel-newbies <kernelnewbies@...linux.org>,
	linux-kernel-mail <linux-kernel@...r.kernel.org>
Subject: Re: typecheck code

On Mon, Jan 31, 2011 at 9:03 AM, Sri Ram Vemulpali
<sri.ram.gmu06@...il.com> wrote:
> Hi all,
>
> /*
>  * Check at compile time that something is of a particular type.
>  * Always evaluates to 1 so you may use it easily in comparisons.
>  */
>  #define typecheck(type,x) \
>  ({      type __dummy; \
>        typeof(x) __dummy2; \
>        (void)(&__dummy == &__dummy2); \
>        1; \
>  })
>
> #define typecheck_fn(type,function) \
> ({      typeof(type) __tmp = function; \
>       (void)__tmp; \
> })
>
> Can anyone help me, explain the above code typecheck. How does
> (void)(&__dummy == &__dummy2) evaluates to 1

Infact I think it will never return 1, since the addresses of __dummy1
and __dummy2 have to be different (off by 4 or 8). As pointed out it
is the next line that always returns 1. The purpose of this line is to
throw away warnings like "Incompatible pointer comparison" or
something like that (haven't tried :-)) incase there is a mismatch.

-- 
Thanks -
Manish
--
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/