Bijoy (bijoyjth@gwu.edu) 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,
Ok,
I believe that I effictively made a confusion between user and kernel space, more precisely between the wrapper C funtion and the real system call.
It's the real system call which has the tag asmlinkage, right ? Like "asmlinkage long sys_open(...)".
Thx for all your responses
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