Various x86 syscall mechanisms

[Jeremy Fitzhardinge <jeremy@goop.org>]

Hi Roland,

As far as I can work out, an x86_32 kernel will use "int 0x80" and 
"sysenter" for system calls.  64-bit kernel will use just "syscall" for 
64-bit processes (though you can use "int 0x80" to access the 32-bit 
syscall interface from a 64-bit process), but will allow "sysenter", 
"syscall" or "int 0x80" for 32-on-64 processes.

Why does 32-on-64 implement 32-bit syscall when native 32-bit doesn't 
seem to?  Or am I overlooking something here?  Does 32-bit also support 
syscall?

Thanks,
    J