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

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Message-ID: <5d2cf6b8-a634-62ea-0b80-1d499aa3c693@fb.com>
Date:   Thu, 24 Oct 2019 17:49:26 +0000
From:   Yonghong Song <yhs@...com>
To:     Ilya Leoshkevich <iii@...ux.ibm.com>,
        Prabhakar Kushwaha <prabhakar.pkin@...il.com>
CC:     "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kselftest@...r.kernel.org" <linux-kselftest@...r.kernel.org>
Subject: Re: Linux-5.4: bpf: test_core_reloc_arrays.o: Segmentation fault with
 llc -march=bpf



On 10/24/19 9:04 AM, Ilya Leoshkevich wrote:
>> Am 23.10.2019 um 03:35 schrieb Prabhakar Kushwaha <prabhakar.pkin@...il.com>:
>>
>>
>> Adding other mailing list, folks...
>>
>> 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://urldefense.proofpoint.com/v2/url?u=https-3A__releases.llvm.org_9.0.0_llvm-2D9.0.0.src.tar.xz&d=DwIFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=se8pV6OlDAeF2g5iEAvSB2qhLBJGPaHADv3NQVNFx6U&s=IzBxNhAvcILfAD_XcSB7t0s6-B-wFY3TBoVGH6WhRK8&e=
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__releases.llvm.org_9.0.0_clang-2Dtools-2Dextra-2D9.0.0.src.tar.xz&d=DwIFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=se8pV6OlDAeF2g5iEAvSB2qhLBJGPaHADv3NQVNFx6U&s=KkjCjWm_q2iMfFh50rTKtFqQEMbRBVhT9Oh8KMfgwW4&e=
>> https://urldefense.proofpoint.com/v2/url?u=https-3A__releases.llvm.org_9.0.0_cfe-2D9.0.0.src.tar.xz&d=DwIFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=DA8e1B5r073vIqRrFz7MRA&m=se8pV6OlDAeF2g5iEAvSB2qhLBJGPaHADv3NQVNFx6U&s=TvkN9sb5rSB5BNxJP27UmCsfNHsRQdaVeAnBa1TkyjM&e=
>>
>> 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 '@...t_core_arrays'
>> #0 0x0000aaaac618db08 llvm::sys::PrintStackTrace(llvm::raw_ostream&)
>> (/usr/local/bin/llc+0x152eb08)
>> Segmentation fault
> 
> Hi,
> 
> FWIW I can confirm that this is happening on s390 too with llvm-project
> commit 950b800c451f.
> 
> Here is the reduced sample that triggers this (with -march=bpf
> -mattr=+alu32):
> 
> struct b {
>    int e;
> } c;
> int f() {
>    return __builtin_preserve_field_info(c.e, 0);
> }
> 
> This is compiled into:
> 
> 0B      bb.0 (%ir-block.0):
> 16B       %0:gpr = LD_imm64 @"b:0:0$0:0"
> 32B       $w0 = COPY %0:gpr, debug-location !17; 1-E.c:5:3
> 48B       RET implicit killed $w0, debug-location !17; 1-E.c:5:3
> 
> and then BPFInstrInfo::copyPhysReg chokes on COPY, since $w0 and %0 are
> in different register classes.

Ilya,

Thanks for reporting. I can reproduce the issue with latest trunk.
I will investigate and fix the problem soon.

Yonghong

> 
> I'm currently bisecting, and also checking whether supporting asymmetric
> copies (like X86 does in CopyToFromAsymmetricReg) would resolve that.
> 
> Best regards,
> Ilya
>