Date: Mon, 17 Feb 2003 02:15:12 -0500 From: Jake Burkholder <jake@locore.ca> To: Bruce Evans <bde@zeta.org.au> Cc: Julian Elischer <julian@elischer.org>, FreeBSD current users <current@FreeBSD.ORG> Subject: Re: question on profiling code Message-ID: <20030217021512.O63597@locore.ca> In-Reply-To: <20030217162950.B4682-100000@gamplex.bde.org>; from bde@zeta.org.au on Mon, Feb 17, 2003 at 05:35:09PM %2B1100 References: <Pine.BSF.4.21.0302161812280.99373-100000@InterJet.elischer.org> <20030217162950.B4682-100000@gamplex.bde.org>
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Apparently, On Mon, Feb 17, 2003 at 05:35:09PM +1100, Bruce Evans said words to the effect of; > On Sun, 16 Feb 2003, Julian Elischer wrote: > > > In addupc_intr, if the increment cannot be done immediatly, the addres > > to increment the count for is stored and the increment is done later at > > ast or userret() time... > > Note that "cannot be done immediatly" is "always except on sparc64's" > under FreeBSD, since incrementing the counter immediately is only > implemented on sparc64's. > > > is there any reason that the address of the PC needs to be stored? > > why is the address from the frame at that time not useable? > > > > is it because the PC in the return frame may be hacked up for signals? > > That's was good a reason as any. I think the next return to user mode > is to the signal handler's context (if there is a signal to be handled). > It would be wrong to use the signal handler's pc. Also, ast() doesn't > have access to the frame, and there is no macro like CLKF_PC() for > general frames. This probably doesn't matter much, since signals are > rare and the hitting on the signal handler's pc would be perfectly > correct if the profiling interrupt occurred an instant later. There are macros for accessing trapframes, like the ones for clockframe, TRAPF_PC etc. > > Now there is a stronger reason: clock interrupt handling is "fast", > so it normally returns to user mode without going near ast(), and the > counter is not updated until the next non-fast interrupt or syscall. In freebsd "fast" interrupts do handle asts, on i386 they return through doreti (you may consider this a bug and have removed it in your version). I see no reason not to just use the pc in the trapframe passed to ast, even in the case of signals they won't be posted until after addupc_task is called. Jake To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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