Hi,

On Sat, Nov 03, 2007 at 11:28:11AM +0000, David Laight wrote:

> The amd64 stub for syscall() is:
> 
> ENTRY(syscall)
> 	movl	%edi,%eax
> 	syscall
> 
> (from libc/arch/x86_64/sys/syscall.S)
> 
> This looks completely wrong to me.
> I think it needs to be:
> 	mov	$0,%eax
> 	mov	%rcx,%r10
> 	syscall
> 
> probably generated by RSYSCALL(syscall)
> 
> I actually suspect there are no actual calls to it in the amd64 userspace.
> 
> Which is rather fortunate since there are calls lurking like:
> 	syscall(SYS___syscall, SYS_foo, args)
> which really isn't going to DTRT unless syscall() is implemented in
> the library - which it cannot be for some architectures like amd64 (& sparc)
> where some, but not all, of the system call arguments are passed in registers.

I'm not sure about this one. But it occurs to me syscall and _syscall can
probably be turned into proper systems calls of their own *, so we don't
have to do the tests in the syscall path. Does that make sense?

Thanks,
Andrew

* ignoring systrace and to a much lesser extent ktrace