Interrupt 0x80 handling

[gerarra at tin.it]

Hi,
giving a look to interrupt 0x80 handling code (i386/i386/exception.s), I've
met FAKE_MCOUNT/MEXITCOUNT system. FAKE_MCOUNT in the end calls _mcount
(libkern/mcount.c) function which seems to be used for profiling purposes
IMHO. It seems (reading comments in sys/gmon.h) that sysctl could be used
to manage syscall profiling (kernel profiling?): Somebody can confirm that
or I've misunderstood? I would like to know another thing too: why interrupt
0x80 handler is implemented through a trap gate? An interrupt gate could
not be more logical?

thanks for answers,
cheers

rookie