Date: Sat, 27 Nov 1999 18:57:28 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: David Greenman <dg@root.com> Cc: Julian Elischer <julian@whistle.com>, current@FreeBSD.ORG Subject: Re: Which is the truth? (sycalls and traps) Message-ID: <199911280257.SAA40292@apollo.backplane.com> References: <199911252215.OAA14800@implode.root.com>
next in thread | previous in thread | raw e-mail | index | archive | help
:>Am I also right in assuming that all the registers that the user was :>running when they did the KERNCALL have been saved on the KERNEL stack by :>the time that the above routines are called? : : No, that's what the pushal (push all) does. : :-DG : :David Greenman pushing/popping integer registers doesn't really take a whole lot of time. The real overhead is with all the junk we have on entering and exiting from a kernel context from/to a user context. In fact, for kernel threads it's even easier: If you are calling the switch code synchronously then, of course, the scratch-on-call registers need not be saved or restored either. It's as simple as the code I've shown below, taken from one of my other projects: pushfl pushl %ebx pushl %ebp pushl %esi pushl %edi pushl $myresumefunction movl %esp,ta_Ctx+mc_SP(%ecx) Switch to new task: movl ta_Ctx+mc_SP(%ecx),%esp ret And the restore function: popl %edi popl %esi popl %ebp popl %ebx popfl ... Enhance as required (i.e. other registers need to be added if an interrupt, segment registers, and so forth. note: pushal/popal does not mess with the segment registers or the FP registers. It is not all-inclusive. Only the main registers are pushed/popped. -Matt Matthew Dillon <dillon@backplane.com> To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199911280257.SAA40292>