On Fri, Jan 8, 2021 at 1:45 AM David Hildenbrand <da...@redhat.com> wrote: > > On 08.01.21 03:20, Nick Desaulniers wrote: > > On Thu, Jan 7, 2021 at 3:27 PM David Hildenbrand <dhild...@redhat.com> > > wrote: > >> > >> > >>> Am 08.01.2021 um 00:21 schrieb Nick Desaulniers <ndesaulni...@google.com>: > >>> > >>> On Thu, Jan 7, 2021 at 3:13 PM David Hildenbrand <da...@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 <ndesaulni...@google.com> > >>>> Cc: Guenter Roeck <li...@roeck-us.net> > >>>> Cc: Christian Borntraeger <borntrae...@de.ibm.com> > >>>> Signed-off-by: David Hildenbrand <da...@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" > >>>> https://lkml.kernel.org/r/20210107202135.52379-1-da...@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?
Right, I suspect that even if ld.lld understood that emulation mode target, it would still fail due to lack of big endian support. We've been building with simply `CC=clang` for s390 linux kernels. Via: https://www.kernel.org/doc/html/latest/kbuild/llvm.html#llvm-utilities we usually start with `make CC=clang` then work our way up to `make LLVM=1`. So you shouldn't need the below patching, just use `CC=clang`. > > 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 > > --- Pulling from your github branch, everything looks good; buildroot support looks good. I'll wire this up to our CI so that we can help report regressions! -- Thanks, ~Nick Desaulniers