-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Hi there people,
I'm trying to figure out for several days now how the following functions:
<from include/asm-i386/thread_info.h>
86 /* how to get the thread information struct from C */
87 static inline struct thread_info *current_thread_info(void)
88 {
89 struct thread_info *ti;
90 __asm__("andl %%esp,%0; ":"=r" (ti) : "" (~(THREAD_SIZE - 1)));
91 return ti;
92 }
I've read several tutorials on inline asm but what is peculiar here is, that
the input operand's constraint is "" (nothing) whereas the (~(THREAD_SIZE-1))
= (~(8192-1)) = (~0001 1111 1111 1111) = 1110 0000 0000 0000, IIRC, gets
passed as a C arg.
What exactly happens here?
I also have another question:
<from include/linux/kernel.h>
203 /**
204 * container_of - cast a member of a structure out to the containing
structure
205 *
206 * @ptr: the pointer to the member.
207 * @type: the type of the container struct this is embedded in.
208 * @member: the name of the member within the struct.
209 *
210 */
211 #define container_of(ptr, type, member) ({ \
212 const typeof( ((type *)0)->member ) *__mptr = (ptr); \
213 (type *)( (char *)__mptr - offsetof(type,member) );})
I can't understand the ((type *)0) part - type is passed as an argument and it
is some struct pointer but the trailing 0 ... what does it actually do?
offsetof is similar:
<from include/linux/stddef.h>
12 #define offsetof(TYPE, MEMBER) ((size_t) &((TYPE *)0)->MEMBER)
Thanks in advance,
Boris.
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.4 (GNU/Linux)
iD8DBQFA4mJsiBySr3Fn37QRArnwAJ40BJugFsZcml0yBFcfte0ioscgvwCglzvb
0yUGR6cEkpOBm1CgnAgMnNQ=
=Ifgz
-----END PGP SIGNATURE-----
--
Kernelnewbies: Help each other learn about the Linux kernel.
Archive: http://mail.nl.linux.org/kernelnewbies/
FAQ: http://kernelnewbies.org/faq/
