Date: Thu, 16 Mar 2017 19:07:39 +0100 From: Sylvain Garrigues <sylvain@sylvaingarrigues.com> To: Andrew Gierth <andrew@tao11.riddles.org.uk>, mmel@freebsd.org, freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: Is CPUTYPE=cortex-A7 supposed to work? Message-ID: <FD2DA030-BDD1-49D3-8471-9DB8DE8E81D3@sylvaingarrigues.com> In-Reply-To: <87pohh2n3c.fsf@news-spur.riddles.org.uk> References: <871suc3nv8.fsf@news-spur.riddles.org.uk> <CANCZdfq4EwH%2B_9FVNai8s6Y-gdTjHJ8dNkJwSrnF%2BSAkdwvYdg@mail.gmail.com> <8737ely05c.fsf@news-spur.riddles.org.uk> <CANCZdfpftVHaPahTOP0vxB-FR%2BKtpqY9JMJr=F2DGifD0fhKMQ@mail.gmail.com> <87wpbxw3yd.fsf@news-spur.riddles.org.uk> <79EBD44B-2C2D-4394-A90C-DF494A049F20@dsl-only.net> <E6BC9F77-F65B-4918-9E22-3BFECA268E30@sylvaingarrigues.com> <674facba-68cd-8ce1-887a-1ef3c51520bc@freebsd.org> <ED8405B6-1150-4A9C-AD93-5C74306FB361@sylvaingarrigues.com> <87pohh2n3c.fsf@news-spur.riddles.org.uk>
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> Le 16 mars 2017 à 18:27, Andrew Gierth <andrew@tao11.riddles.org.uk> a écrit :
>
> tl/dr: building without CPUTYPE is a workaround that simply reduces both
> the chance and severity of failure; building with CPUTYPE currently
> breaks almost everything, but with a probability that varies wildly
> depending on what the application does.
Got it now, thank you both Andrew and Michal. I can’t imagine how lucky we are to have you guys analyze these behaviors so quickly and accurately.
My conclusion of these discussions seems to be:
- Andrew, you proposed a kernel patch which fixes / handles the saving and restoring of FP registers during signal (kernel side). It seems it greatly reduces the failure probability by allowing applications to have FPU instructions in signal handlers. But it breaks ABI.
- Michal, you mentioned you’d like to fix this in a way that doesn’t break ABI, and that:
* the "VFP part of kernel <-> userland interaction is broken from day 1 » <<== was it just this signal part which was broken?
* and "the struct fpreg is also wrong and I'm not sure if or how we can to fix this in compatible way » <<== Andrew’s patch doesn’t fix this right? Is this a serious problem doctor? What are the symptoms?
So what are you guys gonna do about all this, are you going to address these issues, are you going to break the ABI in 12-CURRENT? Can wait to hear about the next steps, the suspense is terrible :-)
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