Vladimir Kuznetsov <ks.vladimir@xxxxxxxxx> writes:
> On Wednesday 13 May 2009 04:58:25 Ian Lance Taylor wrote:
>> Vladimir Kuznetsov <ks.vladimir@xxxxxxxxx> writes:
>> > I have a very small embedded kernel that uses a slightly modified calling
>> > conventions than normal ones on x86-64: it uses r10 instead or rcx to
>> > pass 4th argument and "syscall" instruction instead of normal "call". I
>> > am using a thin wrapper like this:
>> >
>> > error_t __do_syscall(SyscallParams params, ...) __asm__("__do_syscall");
>> > __asm__(
>> > "__do_syscall:\n"
>> > " movq %rcx, %r10\n"
>> > " syscall\n"
>> > " ret\n"
>> > );
>> >
>> > but it requires an additional function call (and so uses an additional
>> > cache line and, possibly, a TLB entry). Are there any way to do it inline
>> > ?
>>
>> You always want to use "syscall" instead of "call"?
> No, "syscall" is used only for system calls. I still have a normal functions
> that are called using standard calling convention.
If you only need it for system calls then I recommend writing an inline
asm statement for each system call, and wrap that inline asm up in an
inline function in a header file somewhere. If you mark the function
with the always_inline attribute then you should get the results you
want.
Ian
