Linux-5.4: bpf: test_core_reloc_arrays.o: Segmentation fault with llc -march=bpf

[Prabhakar Kushwaha <prabhakar.pkin@gmail.com>]

 Adding llvm-bugs@lists.llvm.org mailing list...

Hi All,

I am trying to build kselftest on Linux-5.4 on ubuntu 18.04. I installed
LLVM-9.0.0 and Clang-9.0.0 from below links after following steps from
[1] because of discussion [2]

 https://releases.llvm.org/9.0.0/llvm-9.0.0.src.tar.xz
 https://releases.llvm.org/9.0.0/clang-tools-extra-9.0.0.src.tar.xz
 https://releases.llvm.org/9.0.0/cfe-9.0.0.src.tar.xz

Now, i am trying with llc -march=bpf, with this segmentation fault is
coming as below:

gcc -g -Wall -O2 -I../../../include/uapi -I../../../lib
-I../../../lib/bpf -I../../../../include/generated -DHAVE_GENHDR
-I../../../include -Dbpf_prog_load=bpf_prog_test_load
-Dbpf_load_program=bpf_test_load_program    test_flow_dissector.c
/usr/src/tovards/linux/tools/testing/selftests/bpf/test_stub.o
/usr/src/tovards/linux/tools/testing/selftests/bpf/libbpf.a -lcap -lelf
-lrt -lpthread -o
/usr/src/tovards/linux/tools/testing/selftests/bpf/test_flow_dissector
gcc -g -Wall -O2 -I../../../include/uapi -I../../../lib
-I../../../lib/bpf -I../../../../include/generated -DHAVE_GENHDR
-I../../../include -Dbpf_prog_load=bpf_prog_test_load
-Dbpf_load_program=bpf_test_load_program
test_tcp_check_syncookie_user.c
/usr/src/tovards/linux/tools/testing/selftests/bpf/test_stub.o
/usr/src/tovards/linux/tools/testing/selftests/bpf/libbpf.a -lcap -lelf
-lrt -lpthread -o
/usr/src/tovards/linux/tools/testing/selftests/bpf/test_tcp_check_syncookie_user
gcc -g -Wall -O2 -I../../../include/uapi -I../../../lib
-I../../../lib/bpf -I../../../../include/generated -DHAVE_GENHDR
-I../../../include -Dbpf_prog_load=bpf_prog_test_load
-Dbpf_load_program=bpf_test_load_program    test_lirc_mode2_user.c
/usr/src/tovards/linux/tools/testing/selftests/bpf/test_stub.o
/usr/src/tovards/linux/tools/testing/selftests/bpf/libbpf.a -lcap -lelf
-lrt -lpthread -o
/usr/src/tovards/linux/tools/testing/selftests/bpf/test_lirc_mode2_user
(clang -I. -I./include/uapi -I../../../include/uapi
-I/usr/src/tovards/linux/tools/testing/selftests/bpf/../usr/include
-D__TARGET_ARCH_arm64 -g -idirafter /usr/local/include -idirafter
/usr/local/lib/clang/9.0.0/include -idirafter
/usr/include/aarch64-linux-gnu -idirafter /usr/include
-Wno-compare-distinct-pointer-types -O2 -target bpf -emit-llvm \
-c progs/test_core_reloc_arrays.c -o - || echo "clang failed") | \
llc -march=bpf -mcpu=probe  -filetype=obj -o
/usr/src/tovards/linux/tools/testing/selftests/bpf/test_core_reloc_arrays.o
Stack dump:
0. Program arguments: llc -march=bpf -mcpu=probe -filetype=obj -o
/usr/src/tovards/linux/tools/testing/selftests/bpf/test_core_reloc_arrays.o
1. Running pass 'Function Pass Manager' on module '<stdin>'.
2. Running pass 'BPF Assembly Printer' on function '@test_core_arrays'
#0 0x0000aaaac618db08 llvm::sys::PrintStackTrace(llvm::raw_ostream&)
(/usr/local/bin/llc+0x152eb08)
Segmentation fault
Makefile:260: recipe for target
'/usr/src/tovards/linux/tools/testing/selftests/bpf/test_core_reloc_arrays.o'
failed
make[1]: ***
[/usr/src/tovards/linux/tools/testing/selftests/bpf/test_core_reloc_arrays.o]
Error 139

To add more details,
Commenting following lines in bpf/progs/test_core_reloc_arrays.c
removes the segmentation fault.

--- a/tools/testing/selftests/bpf/progs/test_core_reloc_arrays.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_arrays.c
@@ -41,15 +41,14 @@ int test_core_arrays(void *ctx)
        if (BPF_CORE_READ(&out->a2, &in->a[2]))
                return 1;
        /* in->b[1][2][3] */
-       if (BPF_CORE_READ(&out->b123, &in->b[1][2][3]))
-               return 1;
+//     if (BPF_CORE_READ(&out->b123, &in->b[1][2][3]))
+//             return 1;
        /* in->c[1].c */
        if (BPF_CORE_READ(&out->c1c, &in->c[1].c))
                return 1;
        /* in->d[0][0].d */
-       if (BPF_CORE_READ(&out->d00d, &in->d[0][0].d))
-               return 1;
-
+//     if (BPF_CORE_READ(&out->d00d, &in->d[0][0].d))
+//             return 1;
        return 0;
 }

It looks to be something related llc and more than 1 dimension array.
has anyone faced such error.

Please suggest!!

--prabhakar(pk)

[1]
https://stackoverflow.com/questions/47255526/how-to-build-the-latest-clang-tidy

[2] https://www.mail-archive.com/netdev@vger.kernel.org/msg315096.html


Linux top-commit
----------------
commit bc88f85c6c09306bd21917e1ae28205e9cd775a7 (HEAD -> master,
origin/master, origin/HEAD)
Author: Ben Dooks <ben.dooks@codethink.co.uk>
Date:   Wed Oct 16 12:24:58 2019 +0100

    kthread: make __kthread_queue_delayed_work static

    The __kthread_queue_delayed_work is not exported so
    make it static, to avoid the following sparse warning:

      kernel/kthread.c:869:6: warning: symbol
'__kthread_queue_delayed_work' was not declared. Should it be static?

    Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>