hi about C and asm

hi about C and asm

[lx]

hi all:
     They are some asm codes in the kernel like:

#define set_bit(nr,addr) ({\
register int res __asm__("ax"); \
__asm__ __volatile__("btsl %2,%3\n\tsetb %%al": \
"=a" (res):"0" (0),"r" (nr),"m" (*(addr))); \
res;})


But, almost I can't understand this. So I want to understand asm in C,
which book or website I should learn ?

Thank you
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hi about C and asm

[Augusto Mecking Caringi]

On Tue, May 28, 2013 at 10:02 PM, lx <lxlenovostar@gmail.com> wrote:
> hi all:
>      They are some asm codes in the kernel like:
>
> #define set_bit(nr,addr) ({\
> register int res __asm__("ax"); \
> __asm__ __volatile__("btsl %2,%3\n\tsetb %%al": \
> "=a" (res):"0" (0),"r" (nr),"m" (*(addr))); \
> res;})
>
>
> But, almost I can't understand this. So I want to understand asm in C,
> which book or website I should learn ?

Hi,

    This is a C (preprocessor) macro called set_bit which use GCC
inline assembly in its body.

    http://gcc.gnu.org/onlinedocs/cpp/Macros.html

    http://wiki.osdev.org/Inline_Assembly

-- 
Augusto Mecking Caringi

hi about C and asm

[Jonathan Neuschäfer]

On Wed, May 29, 2013 at 09:02:22AM +0800, lx wrote:
> hi all:
>      They are some asm codes in the kernel like:
> 
> #define set_bit(nr,addr) ({\
> register int res __asm__("ax"); \
> __asm__ __volatile__("btsl %2,%3\n\tsetb %%al": \
> "=a" (res):"0" (0),"r" (nr),"m" (*(addr))); \
> res;})
> 
> 
> But, almost I can't understand this. So I want to understand asm in C,
> which book or website I should learn ?

Google "asm in c", first link is:
http://www.ibiblio.org/gferg/ldp/GCC-Inline-Assembly-HOWTO.html


HTH,
Jonathan Neusch?fer