Comment 25 for bug 1847806
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| bugproxy (bugproxy) wrote Comment bridged from LTC Bugzilla | #25 |
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------- Comment From <email address hidden> 2019-10-15 10:04 EDT-------
From Paul:
I added TCG support for mffsl, mffscrn, mffscrni, mffsce to QEMU, and I think they will appear in QEMU 4.2, which is not yet released.
I found that the support for these instructions were missing because of my efforts to test work I did for GLibC to use those instructions in GLibC 2.30 and GLibC 2.31. It appears that eoan has GLibC 2.30 and has hit these instructions.
Everything I can find says that these instructions exist in DD1 and later versions of POWER9.
> a) do you want us to switch the default emulated CPU to from power9_v2.0 to power8_v2.0 (If so we need the answer asap)?
I'm not sure what the decision criteria is here, but I'll try to offer some information below.
> b) are there known missing/bad instructions in P9-TCG that we should fix by backporting changes?
Making some presumptions...you are looking for how to make QEMU work out of the box for a ppc64el TCG guest. I would hazard that there is some risk to backporting the instructions to QEMU 4.0, but I can't quantify that easily. I think it would be low, but I'm really not that familiar with the QEMU code base.
The other consideration is that if you switch the default, you've perhaps solved the problem in the default case, but POWER9 support would still be broken if somebody tries to use it.
It would seem like the most comprehensive solution is to backport.
BUT, I can't speak to whether there are other instructions missing between QEMU 4.0 and 4.2. :-/ Maybe Leonardo can better speak to a preferred path forward.