19.08.2019. 08.30, "David Gibson" <da...@gibson.dropbear.id.au> је написао/ла: > > On Sun, Aug 18, 2019 at 10:59:01PM +0200, Aleksandar Markovic wrote: > > 18.08.2019. 10.10, "Richard Henderson" <richard.hender...@linaro.org> је > > написао/ла: > > > > > > On 8/16/19 11:59 PM, Aleksandar Markovic wrote: > > > >> From: "Paul A. Clarke" <p...@us.ibm.com> > > > ... > > > >> ISA 3.0B has xscvdpspn leaving its result in word 1 of the target > > > > register, > > > >> and mffprwz expecting its input to come from word 0 of the source > > > > register. > > > >> This sequence fails with QEMU, as a shift is required between those > > two > > > >> instructions. However, the hardware splats the result to both word 0 > > > > and > > > >> word 1 of its output register, so the shift is not necessary. > > > >> Expect a future revision of the ISA to specify this behavior. > > > >> > > > > > > > > Hmmm... Isn't this a gcc bug (using undocumented hardware feature), > > given > > > > everything you said here? > > > > > > The key here is "expect a future revision of the ISA to specify this > > behavior". > > > > > > It's clearly within IBM's purview to adjust the specification to document > > a > > > previously undocumented hardware feature. > > > > > > > By no means, yes, the key is in ISA documentation. But, the impression that > > full original commit message conveys is that the main reason for change is > > gcc behavior. If we accepted in general that gcc behavior determines QEMU > > behavior, I am afraid we would be on a very slippery slope - therefore I > > think the commit message (and possible code comment) should, in my opinion, > > mention ISA docs as the central reason for change. Paul, is there any > > tentative release date of the new ISA specification? > > It's not really a question of gcc behaviour, it's a question of actual > cpu behaviour versus ISA document. Which one qemu should follow is > somewhat debatable, but it sounds here like the ISA will be updated to > match the cpu, which weights it heavily in favour of mimicing the > actual cpu. >
This sounds right to me. Aleksandar > -- > David Gibson | I'll have my music baroque, and my code > david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ > | _way_ _around_! > http://www.ozlabs.org/~dgibson
