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.
> There are no
> command line options to make gcc generate that kind of code. It would
> not be particularly difficult to modify gcc to do it.
Yes, it would not be difficult, but depending on a modified gcc to compile the
code is not a very good thing.
--
Best Regards,
Vladimir
