Date: Sun, 17 Feb 2008 00:20:58 +0100 From: Rafal Jaworowski <raj@semihalf.com> To: Marcel Moolenaar <xcllnt@mac.com> Cc: Marcel Moolenaar <marcel@freebsd.org>, Perforce Change Reviews <perforce@freebsd.org> Subject: Re: PERFORCE change 135517 for review Message-ID: <47B76FDA.7070008@semihalf.com> In-Reply-To: <EDF429F2-E803-4FA7-A387-3A53D15A21F2@mac.com> References: <200802162141.m1GLfgkj048217@repoman.freebsd.org> <47B75EB3.2020001@semihalf.com> <504560A3-EABB-4896-8B3E-C7FC89F31EFB@mac.com> <47B76A8E.5060607@semihalf.com> <EDF429F2-E803-4FA7-A387-3A53D15A21F2@mac.com>
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Marcel Moolenaar wrote: >>>>> >>>>> Save U-Boot's registers at startup and restore them when >>>>> performing a syscall. This way we don't have to compile >>>>> code specially to avoid using those registers. Otherwise >>>>> we have to encode knowledge of those registers in at least >>>>> 4 makefiles and introduce a build knob to enable it all. >>>>> This does not allow us to build everything with a single >>>>> build world. >>>>> >>>> >>>> Hi Marcel, >>>> >>>> I'm not quite sure this is sufficient... I already had a similar >>>> save/restore >>>> in place, but there is some general problem with U-Boot that leads to >>>> hangs >>>> (experienced): >>> >>> Interesting, I didn't see any such problems with 1.3.2-rc1. >>> >> >> Chances are it might not surface, depending on the regs usage pattern, >> compiler etc., for example a -O0 build would usually hide this issue, >> but in >> principle those regs are not exception/interrupt safe. > > Agreed. I didn't see it at -O2, BTW. > When I was looking at this it also did not always pop up (with -O2 too), although typically when loader(8) was executed and left idle for some time it would hang sooner or later. > We can disable interrupts when not running in U-Boot, right? > The impact should be marginal... > Yes, this could be worked around like this, but with degraded functionality: all timer-related calls from the API would not make sense, and things like autoboot count down will not work. Even worse, the [polled] networking might not work at all if decrementer was shut, as we'd not be able to time out while waiting on the packet, status registers' change and so on. I think this issue needs some further investigation and proper resolution. Rafal
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