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Re: [PULL 11/24] tcg/optimize: Use tcg_constant_internal with constant f

From: Richard Henderson
Subject: Re: [PULL 11/24] tcg/optimize: Use tcg_constant_internal with constant folding
Date: Wed, 3 Feb 2021 16:22:04 -1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0

On 2/1/21 10:45 AM, Richard W.M. Jones wrote:
> This commit breaks running certain s390x binaries, at least
> the "mount" command (or a library it uses) breaks.
> More details in this BZ:
> https://bugzilla.redhat.com/show_bug.cgi?id=1922248
> Could we revert this change since it seems to have caused other
> problems as well?

Well, the other problems have been fixed (which were in fact latent, and could
have been produced by other means).  I would not like to sideline this patch
set indefinitely.

Could you give me some help extracting the relevant binaries?  "Begin with an
s390x host" is a non-starter.

FWIW, with qemu-system-s390x, booting debian, building qemu-s390x, and running
"/bin/mount -t proc proc /mnt" under double-emulation does not show the bug.

I suspect that's because debian targets a relatively old s390x cpu, and that
yours is using the relatively new vector instructions.  But I don't know.

What I do know is that current qemu doesn't seem to boot current fedora:

 $ ../bld/qemu-system-s390x -nographic -m 4G -cpu max -drive
 qemu-system-s390x: warning: 'msa5-base' requires 'kimd-sha-512'.
 qemu-system-s390x: warning: 'msa5-base' requires 'klmd-sha-512'.
 LOADPARM=[        ]
 Using virtio-blk.
 ISO boot image size verified

 KASLR disabled: CPU has no PRNG
 Linux version 5.8.15-301.fc33.s390x
(mockbuild@buildvm-s390x-07.s390.fedoraproject.org) 1 SMP Thu Oct 15 15:55:57
UTC 2020Kernel fault: interruption code 0005 ilc:2
 PSW : 0000200180000000 00000000000124c4
       R:0 T:0 IO:0 EX:0 Key:0 M:0 W:0 P:0 AS:0 CC:2 PM:0 RI:0 EA:3
 GPRS: 0000000000000000 0000000b806a2da6 7aa19c5cbb980703 95f62d65812b83ab
       d5e42882af203615 0000000b806a2da0 0000000000000000 0000000000000000
       00000000000230e8 0000000001438500 0000000001720320 0000000000000000
       0000000001442718 0000000000010070 0000000000012482 000000000000bf20

Which makes me thing that fedora 33 is now targeting a cpu that is too new and
not actually supported by tcg.


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