Date: Thu, 12 Aug 2004 19:06:05 -0700 (PDT) From: Matthew Dillon <dillon@apollo.backplane.com> To: gerarra@tin.it Cc: freebsd-hackers@freebsd.org Subject: Re: Interrupt 0x80 handling Message-ID: <200408130206.i7D265rq005367@apollo.backplane.com> References: <4119722900001B0D@ims3a.cp.tin.it>
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: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
An interrupt gate will disable interrupts on entry (cli equivalent),
while a trap gate does not. There is no reason to disable interrupts
in a system call so a trap gate is used.
-Matt
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