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

[Andrii Nakryiko]

On Tue, Dec 21, 2021 at 5:33 PM Pu Lehui <pulehui@xxxxxxxxxx> wrote:
>
>
>
> On 2021/12/22 7:52, Andrii Nakryiko wrote:
> > On Mon, Dec 20, 2021 at 4:58 PM Pu Lehui <pulehui@xxxxxxxxxx> 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@xxxxxxxxxx> wrote:
> >>>>>
> >>>>>
> >>>>>
> >>>>> On 2021/12/16 12:06, Andrii Nakryiko wrote:
> >>>>>> On Tue, Dec 14, 2021 at 5:54 AM Pu Lehui <pulehui@xxxxxxxxxx> 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.

I see. Can you try adding something like:

ARCH_APIDIR := $(abspath ../../../../arch/$(SRCARCH)/include/uapi)

and then add -I$(ARCH_APIDIR) to BPF_CFLAGS?

Please let me know if that works for your cross-compilation case.

> >>>>>
> >>>>> --- 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@xxxxxxxxxx>
> >>>>>>> ---
> >>>>>>>     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(-)
> >>>>>>>
> >>>>>>
> >>>>>> [...]
> >>>>>> .
> >>>>>>
> >>>> .
> >>>>
> >>> .
> > .
> >