Hi, Le Sat, 3 Nov 2007 13:33:12 +0000, ninjaboy <n0b0dyn1nj4@xxxxxxxxx> a écrit : > I've seen that there are two section (.altinstructions and > .altinstr_replacement), there are some "polimorphic" code that is > replaced at runtime, now in arch/x86_64/lib/copy_user.S there are > copy_user_generic_unrolled and copy_user_generic_string, that replaces > the function that is used, my question is: where and how the decision > on what code is used (in this case > copy_user_generic_unrolled or copy_user_generic_string) for replace > code? Here: http://lxr.free-electrons.com/source/arch/x86_64/lib/copy_user.S#046 with the following line: ALTERNATIVE_JUMP X86_FEATURE_REP_GOOD,copy_user_generic_unrolled,copy_user_generic_string with the ALTERNATIVE_JUMP macro being defined at the top of the copy_user.S file. It adds: * code to the normal text section to call the "default" function, the unrolled version ; * code to the altinstr_replacement section to call the copy_user_generic_string function ; * informations to the altinstructions section, which is processed at boot time by arch/i386/kernel/alternative.c in order to know if an alternative must be applied or not, depending on the presence/absence on some processor features (here X86_FEATURE_REP_GOOD) Sincerly, Thomas -- Thomas Petazzoni - thomas.petazzoni@xxxxxxxx http://{thomas,sos,kos}.enix.org - http://www.toulibre.org http://www.{livret,agenda}dulibre.org -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
