| 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
| ||
|
Message-Id: <E1HrzHL-0000s2-Pv@be1.lrz>
Date: Sat, 26 May 2007 18:38:07 +0200
From: Bodo Eggert <7eggert@....de>
To: Jan Engelhardt <jengelh@...ux01.gwdg.de>,
David Miller <davem@...emloft.net>, satyam.sharma@...il.com,
linux-kernel@...r.kernel.org
Subject: Re: double exclamation (!!) suckage in the kernel
Jan Engelhardt <jengelh@...ux01.gwdg.de> wrote:
> On May 25 2007 14:14, David Miller wrote:
>>"!!" is used in contexts where pointers might be being
>>tested as well as plain integers, the "!!" turns a pointer
>>into the equivalent integer boolean for testing.
>>
>>NULL pointers become 0
>>non-NULL pointers become 1
>
> Though,
> if(!!ptr)
> is effectively the same as
> if(ptr)
Not exactly, if(foo) is the same as if( (int) foo), which is not
guaranteed to result in non-null values for non-null pointers.
ISO 9899/1999 says: "Any pointer may be converted to an integer type. [...]
The result need not be in the range of values of any integer type."
"if(!!foo)" is the same as "if(0 == (0 == foo))", which is (I asume) the same
as "if(0 == ((type_of_foo)NULL == foo))", or if((type_of_foo)NULL != foo).
--
Funny quotes:
11. Atheism is a non-prophet orgainization.
Friß, Spammer: bj@...CYWgi.7eggert.dyndns.org IsWw@...jh45.7eggert.dyndns.org
-
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/
Powered by blists - more mailing lists