Re: [PATCH v1] s390x/tcg: Fix RISBHG

[David Hildenbrand]

On 08.01.21 10:44, David Hildenbrand wrote:
> On 08.01.21 03:20, Nick Desaulniers wrote:
>> On Thu, Jan 7, 2021 at 3:27 PM David Hildenbrand <dhildenb@redhat.com> wrote:
>>>
>>>
>>>> Am 08.01.2021 um 00:21 schrieb Nick Desaulniers <ndesaulniers@google.com>:
>>>>
>>>> On Thu, Jan 7, 2021 at 3:13 PM David Hildenbrand <david@redhat.com> wrote:
>>>>>
>>>>> RISBHG is broken and currently hinders clang builds of upstream kernels
>>>>> from booting: the kernel crashes early, while decompressing the image.
>>>>>
>>>>>  [...]
>>>>>   Kernel fault: interruption code 0005 ilc:2
>>>>>   Kernel random base: 0000000000000000
>>>>>   PSW : 0000200180000000 0000000000017a1e
>>>>>         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: 0000000000000001 0000000c00000000 00000003fffffff4 
>>>>> 00000000fffffff0
>>>>>         0000000000000000 00000000fffffff4 000000000000000c 
>>>>> 00000000fffffff0
>>>>>         00000000fffffffc 0000000000000000 00000000fffffff8 
>>>>> 00000000008e25a8
>>>>>         0000000000000009 0000000000000002 0000000000000008 
>>>>> 000000000000bce0
>>>>>
>>>>> One example of a buggy instruction is:
>>>>>
>>>>>    17dde:       ec 1e 00 9f 20 5d       risbhg  %r1,%r14,0,159,32
>>>>>
>>>>> With %r14 = 0x9 and %r1 = 0x7 should result in %r1 = 0x900000007, however,
>>>>> results in %r1 = 0.
>>>>>
>>>>> Let's interpret values of i3/i4 as documented in the PoP and make
>>>>> computation of "mask" only based on i3 and i4 and use "pmask" only at the
>>>>> very end to make sure wrapping is only applied to the high/low doubleword.
>>>>>
>>>>> With this patch, I can successfully boot a v5.10 kernel built with
>>>>> clang, and gcc builds keep on working.
>>>>>
>>>>> Fixes: 2d6a869833d9 ("target-s390: Implement RISBG")
>>>>> Reported-by: Nick Desaulniers <ndesaulniers@google.com>
>>>>> Cc: Guenter Roeck <linux@roeck-us.net>
>>>>> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
>>>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>>>> ---
>>>>>
>>>>> This BUG was a nightmare to debug and the code a nightmare to understand.
>>>>>
>>>>> To make clang/gcc builds boot, the following fix is required as well on
>>>>> top of current master: "[PATCH] target/s390x: Fix ALGSI"
>>>>> 20210107202135.52379-1-david@redhat.com">https://lkml.kernel.org/r/20210107202135.52379-1-david@redhat.com
>>>>
>>>> In that case, a huge thank you!!! for this work! ++beers_owed.
>>>>
>>>
>>> :) a kernel build for z13 should work with the (default) „-cpu qemu“ cpu 
>>> type.
>>
>> Hmm...so I don't think clang can build a Linux kernel image with
>> CONFIG_MARCH_Z13=y just yet; just defconfig.  Otherwise looks like
>> clang barfs on some of the inline asm constraints.
>>
> 
> Ah, right. I overwrote my manual config by a temporary defconfig :)
> 
> 
> So, I'm on x86-64 F33.
> 
> clang version 11.0.0 (Fedora 11.0.0-2.fc33)
> LLVM version 11.0.0
> 
> I cannot directly use "LLVM=1" for cross-compilation, as I keep getting
> "error: unknown emulation: elf64_s390" from ld.lld and "error: invalid
> output format: 'elf64-s390'" from llvm-objcopy. I assume that's fixed in
> llvm12?
> 
> 1. I patch around it (strange, I remember CC= .. used to work, but it no
> longer does)
> 
> ---
> 
> index e30cf02da8b8..89c57062ed5d 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -427,13 +427,13 @@ KBUILD_HOSTLDLIBS   := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
>  CPP            = $(CC) -E
>  ifneq ($(LLVM),)
>  CC             = clang
> -LD             = ld.lld
> -AR             = llvm-ar
> -NM             = llvm-nm
> -OBJCOPY                = llvm-objcopy
> -OBJDUMP                = llvm-objdump
> -READELF                = llvm-readelf
> -STRIP          = llvm-strip
> +LD             = $(CROSS_COMPILE)ld
> +AR             = $(CROSS_COMPILE)ar
> +NM             = $(CROSS_COMPILE)nm
> +OBJCOPY                = $(CROSS_COMPILE)objcopy
> +OBJDUMP                = $(CROSS_COMPILE)objdump
> +READELF                = $(CROSS_COMPILE)readelf
> +STRIP          = $(CROSS_COMPILE)strip
>  else
>  CC             = $(CROSS_COMPILE)gcc
>  LD             = $(CROSS_COMPILE)ld
> 
> ---
> 
> 2. Compile using clang
> 
> 
> Using latest linux-next (1c925d2030afd354a02c23500386e620e662622b) +
> above patch
> 
> ---
> 
> #!/bin/bash
> export ARCH=s390;
> export CROSS_COMPILE=s390x-linux-gnu-
> export LLVM=1
> make distclean
> make defconfig
> 
> # Make F32 initrd boot without inserting modules
> ./scripts/config -e CONFIG_SCSI_ISCSI_ATTRS
> ./scripts/config -e CONFIG_ISCSI_TCP
> 
> make -j40 > /dev/null
> 
> ---
> 
> 3. Run it via QEMU. I boot a full Fedora 32 using the cloud-image +
> initrd from Fedora 32 (tried to stick to your cmdline where possible)
> 
> ./build/qemu-system-s390x \
> -m 512M \
> -cpu qemu \
> -display none \
> -nodefaults \
> -kernel ../linux-cross/arch/s390/boot/bzImage \
> -append "root=/dev/vda1 conmode=sclp console=ttyS0" \
> -initrd ../Fedora-Cloud-Base-32-1.6.x86_64-initrd.img \
> -hda ../Fedora-Cloud-Base-32-1.6.x86_64-initrd.img \

^ -hda ../Fedora-Cloud-Base-32-1.6.x86_64.qcow2 \


-- 
Thanks,

David / dhildenb