Re: asmlinkage

[Christophe Lucas <c.lucas@xxxxxxxxxxx>]

Bijoy (bijoyjth@xxxxxxx) wrote:
> 
> > You are probably confusing the user-space and the kernel-space side of
> > the thing. On the user-side, the wrapper takes arguments from the stack
> > and loads them to the registers. And calls the trap. Now the kernel
> > parts comes to play. It does some setup and calls the sys_* function.
> > But the arguments are still in registers. So the asmlinkage tells the
> > compiler, that the function will have the args in registers and not on
> > the stack, as would be expected for C function.
> 
> Isnt it the other way around .... when the sys_* function is called .. the 
> arguments are on the stack .... the syscall handler saves the register 
> arguments (SAVE_ALL) and then invokes the actual syscall .... asmlinkage 
> means that the arguments are on the stack and not in registers .... plz 
> correct me if i am wrong.

Hi,

As I can understand about syscall and asmlinkage:
From user space, syscall's arguments are stored in registers, and number
of syscall are in eax.
x80 int are launched, and arch/i386/entry.S come to ENTRY(system_call)
and arguments are pushed on stack.
sys_ functions are called from address stored in sys_call_table.
Then the sys_ function is executed and asmlinkage say to not optimized
the arguments and to take arguments from stack.

If I make a mistake, I will happy you give me the right way.

Regards,
-- 
Amicalement

Christophe 

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