Date: Sat, 16 Feb 2008 23:58:22 +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: <47B76A8E.5060607@semihalf.com> In-Reply-To: <504560A3-EABB-4896-8B3E-C7FC89F31EFB@mac.com> References: <200802162141.m1GLfgkj048217@repoman.freebsd.org> <47B75EB3.2020001@semihalf.com> <504560A3-EABB-4896-8B3E-C7FC89F31EFB@mac.com>
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Marcel Moolenaar wrote: >>> Change 135517 by marcel@marcel_jnpr on 2008/02/16 21:41:02 >>> >>> 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. >> - U-Boot does not handle interrupts so there's no context save/restore of >> exceptions, other than very few cases >> >> - there's one paricular asynchronous way for U-Boot code to regain >> control >> without those dedicated r14/29 regs saved: decrementer, which can hit >> anytime >> while in the app code, and which usually leads to hangs/corruption as >> U-Boot >> code use them blindly > > It's really best if U-Boot deals with that. > Yes, but it doesn't right now, so IMO the right way to go is first fixing u-boot and only after that eliminating the -ffixed safety measures and I think we should revert those last changes until u-boot exceptions handle the dedicated regs properly. Rafal
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