netdev - Re: [PATCH bpf-next] selftests/bpf: Fix building error when using userspace pt

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Date:   Wed, 22 Dec 2021 09:33:27 +0800
From:   Pu Lehui <pulehui@...wei.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, Martin Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        john fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Shuah Khan <shuah@...nel.org>,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next] selftests/bpf: Fix building error when using
 userspace pt_regs



On 2021/12/22 7:52, Andrii Nakryiko wrote:
> On Mon, Dec 20, 2021 at 4:58 PM Pu Lehui <pulehui@...wei.com> wrote:
>>
>>
>>
>> On 2021/12/20 22:02, Pu Lehui wrote:
>>>
>>>
>>> On 2021/12/18 0:45, Andrii Nakryiko wrote:
>>>> On Thu, Dec 16, 2021 at 6:25 PM Pu Lehui <pulehui@...wei.com> wrote:
>>>>>
>>>>>
>>>>>
>>>>> On 2021/12/16 12:06, Andrii Nakryiko wrote:
>>>>>> On Tue, Dec 14, 2021 at 5:54 AM Pu Lehui <pulehui@...wei.com> wrote:
>>>>>>>
>>>>>>> When building bpf selftests on arm64, the following error will occur:
>>>>>>>
>>>>>>> progs/loop2.c:20:7: error: incomplete definition of type 'struct
>>>>>>> user_pt_regs'
>>>>>>>
>>>>>>> Some archs, like arm64 and riscv, use userspace pt_regs in
>>>>>>> bpf_tracing.h, which causes build failure when bpf prog use
>>>>>>> macro in bpf_tracing.h. So let's use vmlinux.h directly.
>>>>>>
>>>>>> We could probably also extend bpf_tracing.h to work with
>>>>>> kernel-defined pt_regs, just like we do for x86 (see __KERNEL__ and
>>>>>> __VMLINUX_H__ checks). It's more work, but will benefit other end
>>>>>> users, not just selftests.
>>>>>>
>>>>> It might change a lot. We can use header file directory generated by
>>>>> "make headers_install" to fix it.
>>>>
>>>> We don't have dependency on "make headers_install" and I'd rather not
>>>> add it.
>>>>
>>>> What do you mean by "change a lot"?
>>>>
>>> Maybe I misunderstood your advice. Your suggestion might be to extend
>>> bpf_tracing.h to kernel-space pt_regs, while some archs, like arm64,
> 
> yes
> 
>>> only support user-space. So the patch might be like this:
>>>
>>> diff --git a/tools/lib/bpf/bpf_tracing.h b/tools/lib/bpf/bpf_tracing.h
>>> index db05a5937105..2c3cb8e9ae92 100644
>>> --- a/tools/lib/bpf/bpf_tracing.h
>>> +++ b/tools/lib/bpf/bpf_tracing.h
>>> @@ -195,9 +195,13 @@ struct pt_regs;
>>>
>>>    #elif defined(bpf_target_arm64)
>>>
>>> -struct pt_regs;
>>> +#if defined(__KERNEL__)
>>> +#define PT_REGS_ARM64 const volatile struct pt_regs
>>> +#else
>>>    /* arm64 provides struct user_pt_regs instead of struct pt_regs to
>>> userspace */
>>>    #define PT_REGS_ARM64 const volatile struct user_pt_regs
>>> +#endif
>>> +
>>>    #define PT_REGS_PARM1(x) (((PT_REGS_ARM64 *)(x))->regs[0])
>>>    #define PT_REGS_PARM2(x) (((PT_REGS_ARM64 *)(x))->regs[1])
>>>    #define PT_REGS_PARM3(x) (((PT_REGS_ARM64 *)(x))->regs[2])
>>>
>> Please ignore the last reply. User-space pt_regs of arm64/s390 is the
>> first part of the kernel-space's, it should has covered both kernel and
>> userspace.
> 
> Alright, so is there still a problem or not? Looking at the definition
> of struct pt_regs for arm64, just casting struct pt_regs to struct
> user_pt_regs will indeed just work. So in that case, what was your
> original issue?
> 
Thanks for your reply. The original issue is, when arm64 bpf selftests 
cross compiling in x86_64 host, clang cannot find the arch specific uapi 
ptrace.h, and then the above error occur. Of course it works when 
compiling in arm64 host for it owns the corresponding uapi ptrace.h. So 
my suggestion is to add arch specific use header file directory 
generated by "make headers_install" for the cross compiling issue.
>>>>>
>>>>> --- a/tools/testing/selftests/bpf/Makefile
>>>>> +++ b/tools/testing/selftests/bpf/Makefile
>>>>> @@ -294,7 +294,8 @@ MENDIAN=$(if
>>>>> $(IS_LITTLE_ENDIAN),-mlittle-endian,-mbig-endian)
>>>>>     CLANG_SYS_INCLUDES = $(call get_sys_includes,$(CLANG))
>>>>>     BPF_CFLAGS = -g -D__TARGET_ARCH_$(SRCARCH) $(MENDIAN) \
>>>>>                -I$(INCLUDE_DIR) -I$(CURDIR) -I$(APIDIR) \
>>>>> -            -I$(abspath $(OUTPUT)/../usr/include)
>>>>> +            -I$(abspath $(OUTPUT)/../usr/include) \
>>>>> +            -I../../../../usr/include
>>>>>>>
>>>>>>> Signed-off-by: Pu Lehui <pulehui@...wei.com>
>>>>>>> ---
>>>>>>>     tools/testing/selftests/bpf/progs/loop1.c     |  8 ++------
>>>>>>>     tools/testing/selftests/bpf/progs/loop2.c     |  8 ++------
>>>>>>>     tools/testing/selftests/bpf/progs/loop3.c     |  8 ++------
>>>>>>>     tools/testing/selftests/bpf/progs/loop6.c     | 20
>>>>>>> ++++++-------------
>>>>>>>     .../selftests/bpf/progs/test_overhead.c       |  8 ++------
>>>>>>>     .../selftests/bpf/progs/test_probe_user.c     |  6 +-----
>>>>>>>     6 files changed, 15 insertions(+), 43 deletions(-)
>>>>>>>
>>>>>>
>>>>>> [...]
>>>>>> .
>>>>>>
>>>> .
>>>>
>>> .
> .
>