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: <55249A65.8080304@dei.uc.pt> Date: Wed, 08 Apr 2015 04:03:01 +0100 From: Samuel Neves <sneves@....uc.pt> To: discussions@...sword-hashing.net Subject: Re: [PHC] On type aliasing and similar issues On 04/08/2015 03:37 AM, Alexander Cherepanov wrote: > AFACT this is implementation-defined in C89 (3.3.2.3) and fully defined in C99 and C11 (6.5.2.3p3). Yes, type punning with unions is now OK (though implementation-defined; accessing the wrong member may still trap) in C99 and above. What is being dereferenced in the example is the pointer to the union, not the members, so I'm not sure strict aliasing's undefined behavior applies. The example could be further improved to demonstrate this: #include <stdint.h> #include <stdio.h> union U { uint32_t x[2]; uint64_t y; }; extern union U * v; void f() { uint32_t * p = &v->x[0]; uint64_t * q = &v->y; *p = 17; *q = 42; printf("%u\n", v->x[0]); } While Clang and recent GCC do what one would hope (print 42), GCC 3.4 and Intel compiler print 17.
Powered by blists - more mailing lists