Re: Illegal operation with clang + CONFIG_MARCH_Z13

[Christian Borntraeger]

Am 13.09.22 um 19:34 schrieb Nathan Chancellor:
> Hi all,
>
> Recently, Fedora moved their baseline from CONFIG_MARCH_ZEC12 to
> CONFIG_MARCH_Z13:
>
> https://src.fedoraproject.org/rpms/kernel/c/aff6e8acdaa437e9f06ef4166ca2209071223f8d
>
> Unfortunately, this causes clang built kernels to have an "illegal
> operation" panic when booting in QEMU. This is trivially reproducible on
> mainline with the versions of clang that s390 supports.
>
> # Switch from CONFIG_MARCH_ZEC12 to CONFIG_MARCH_Z13
> $ make -skj"$(nproc)" ARCH=s390 CC=clang CROSS_COMPILE=s390x-linux-gnu- 
> defconfig menuconfig bzImage
>
> $ qemu-system-s390x \
> -M s390-ccw-virtio \
> -kernel arch/s390/boot/bzImage \
> -display none \
> -initrd .../boot-utils/images/s390/rootfs.cpio \
> -m 512m \
> -nodefaults \
> -no-reboot \
> -serial mon:stdio
> ...
> [    0.558817] Linux version 6.0.0-rc5-00017-gd1221cea11fc 
> (nathan@distrobox-oTN5YGrt3J.thelio-3990X) (clang version 14.0.5 (Fedora 
> 14.0.5-7.fc38), GNU ld version 2.38-4.fc37) #1 SMP Tue Sep 13 08:35:38 MST 2022
> ...
> [    1.675787] illegal operation: 0001 ilc:3 [#1] SMP
> [    1.675888] Modules linked in:
> [    1.676044] CPU: 0 PID: 59 Comm: modprobe Not tainted 
> 6.0.0-rc5-00017-gd1221cea11fc #1
> [    1.676134] Hardware name: QEMU 8561 QEMU (KVM/Linux)

What qemu version is that and what command line did you use (any cpu model?)

> [    1.676202] Krnl PSW : 0704d00180000000 0000000000579fbc 
> (load_elf_binary+0x31c/0x11c0)
> [    1.676459]            R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:1 PM:0 
> RI:0 EA:3
> [    1.676489] Krnl GPRS: 0000000000000001 00000000044f0000 0000000000000000 
> 0000000000000000
> [    1.676506]            8000000000000080 0000000000000000 0000000000000000 
> 00000000035fa900
> [    1.676522]            0000000000000001 000000000353ce00 0000000000000001 
> 00000000044693c0
> [    1.676538]            000000000276fa00 000000000446a000 0000000000579f9e 
> 00000380002ebc78
> [    1.677128] Krnl Code: 0000000000579fac: a7f405b8            brc     
> 15,000000000057ab1c
> [    1.677128]            0000000000579fb0: e31003400004        lg      %r1,832
> [    1.677128]           #0000000000579fb6: e3001780003b        lzrf    
> %r0,1920(%r1)

QEMU does support lzrf as far asI can tell as soon as you have 
S390_FEAT_STFLE_53 which is part
of the qemu_V4_1 cpu model.

> [    1.677128]           >0000000000579fbc: 50001780            st      
> %r0,1920(%r1)
> [    1.677128]            0000000000579fc0: e31003400004        lg      %r1,832
> [    1.677128]            0000000000579fc6: c40800aa99a9        lgrl    
> %r0,0000000001acd318
> [    1.677128]            0000000000579fcc: e3001d400124        stg     
> %r0,7488(%r1)
> [    1.677128]            0000000000579fd2: e31003400004        lg      %r1,832
> [    1.677343] Call Trace:
> [    1.677564]  [<0000000000579fbc>] load_elf_binary+0x31c/0x11c0
> [    1.677635] ([<0000000000579f9e>] load_elf_binary+0x2fe/0x11c0)
> [    1.677652]  [<00000000004e1ae6>] bprm_execve+0x4f6/0x7b0
> [    1.677671]  [<00000000004e1256>] kernel_execve+0x3b6/0x3d0
> [    1.677687]  [<000000000017e1c8>] call_usermodehelper_exec_async+0x158/0x1d0
> [    1.677706]  [<0000000000103a9a>] __ret_from_fork+0x3a/0x60
> [    1.677719]  [<0000000000f8562a>] ret_from_fork+0xa/0x40
> [    1.677748] Last Breaking-Event-Address:
> [    1.677757]  [<0000000000579fa2>] load_elf_binary+0x302/0x11c0
> [    1.678012] Kernel panic - not syncing: Fatal exception: panic_on_oops
>
> The rootfs image is available in our boot-utils repo [1], should it be
> necessary for reproducing this issue. I do not see any problems with
> booting a CONFIG_MARCH_Z13 kernel compiled with GCC 12.2.1 from Fedora
> but it is possible that clang and GCC generate different code. I am not
> sure if this is a compiler problem or an emulation one, which is where I
> was looking for some input from you all.
>
> [1]: https://github.com/ClangBuiltLinux/boot-utils
>
> Cheers,
> Nathan