Re: [PATCH 4/3] selftests/hid: more fixes to build with older kernel

[Justin Stitt]

Eduard,

On Fri, Aug 25, 2023 at 11:54 AM Eduard Zingerman <eddyz87@xxxxxxxxx> wrote:
>
> On Fri, 2023-08-25 at 18:23 +0000, Justin Stitt wrote:
> > On Fri, Aug 25, 2023 at 10:36:30AM +0200, Benjamin Tissoires wrote:
> > > These fixes have been triggered by [0]:
> > > basically, if you do not recompile the kernel first, and are
> > > running on an old kernel, vmlinux.h doesn't have the required
> > > symbols and the compilation fails.
> > >
> > > The tests will fail if you run them on that very same machine,
> > > of course, but the binary should compile.
> > >
> > > And while I was sorting out why it was failing, I realized I
> > > could do a couple of improvements on the Makefile.
> > >
> > > [0] https://lore.kernel.org/linux-input/56ba8125-2c6f-a9c9-d498-0ca1c153dcb2@xxxxxxxxxx/T/#t
> > >
> > > Signed-off-by: Benjamin Tissoires <bentiss@xxxxxxxxxx>
> > > ---
> > > Benjamin Tissoires (3):
> > >       selftests/hid: ensure we can compile the tests on kernels pre-6.3
> > >       selftests/hid: do not manually call headers_install
> > >       selftests/hid: force using our compiled libbpf headers
> > >
> > >  tools/testing/selftests/hid/Makefile                | 10 ++++------
> > >  tools/testing/selftests/hid/progs/hid.c             |  3 ---
> > >  tools/testing/selftests/hid/progs/hid_bpf_helpers.h | 20 ++++++++++++++++++++
> > >  3 files changed, 24 insertions(+), 9 deletions(-)
> > > ---
> > > base-commit: 1d7546042f8fdc4bc39ab91ec966203e2d64f8bd
> > > change-id: 20230825-wip-selftests-9a7502b56542
> > >
> > > Best regards,
> > > --
> > > Benjamin Tissoires <bentiss@xxxxxxxxxx>
> > >
> >
> > Benjamin, thanks for the work here. Your series fixed up _some_ of the
> > errors I had while building on my 6.3.11 kernel. I'm proposing a single
> > patch that should be applied on top of your series that fully fixes
> > _all_ of the build errors I'm experiencing.
> >
> > Can you let me know if it works and potentially formulate a new series
> > so that `b4 shazam` applies it cleanly?
> >
> > PATCH BELOW
> > ---
> > From 5378d70e1b3f7f75656332f9bff65a37122bb288 Mon Sep 17 00:00:00 2001
> > From: Justin Stitt <justinstitt@xxxxxxxxxx>
> > Date: Fri, 25 Aug 2023 18:10:33 +0000
> > Subject: [PATCH 4/3] selftests/hid: more fixes to build with older kernel
> >
> > I had to use the clever trick [1] on some other symbols to get my builds
> > working.
> >
> > Apply this patch on top of Benjamin's series [2].
> >
> > This is now a n=4 patch series which has fixed my builds when running:
> > > $ make LLVM=1 -j128 ARCH=x86_64 mrproper headers
> > > $ make LLVM=1 -j128 ARCH=x86_64 -C tools/testing/selftests TARGETS=hid
> >
> > [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf/progs/bpf_iter.h#n3
> > [2]: https://lore.kernel.org/all/20230825-wip-selftests-v1-0-c862769020a8@xxxxxxxxxx/
> > Signed-off-by: Justin Stitt <justinstitt@xxxxxxxxxx>
> > ---
> >  .../selftests/hid/progs/hid_bpf_helpers.h     | 29 +++++++++++++++++++
> >  1 file changed, 29 insertions(+)
> >
> > diff --git a/tools/testing/selftests/hid/progs/hid_bpf_helpers.h b/tools/testing/selftests/hid/progs/hid_bpf_helpers.h
> > index 749097f8f4d9..e2eace2c0029 100644
> > --- a/tools/testing/selftests/hid/progs/hid_bpf_helpers.h
> > +++ b/tools/testing/selftests/hid/progs/hid_bpf_helpers.h
> > @@ -7,12 +7,26 @@
> >
> >  /* "undefine" structs in vmlinux.h, because we "override" them below */
> >  #define hid_bpf_ctx hid_bpf_ctx___not_used
> > +#define hid_report_type hid_report_type___not_used
> > +#define hid_class_request hid_class_request___not_used
> > +#define hid_bpf_attach_flags hid_bpf_attach_flags___not_used
> >  #include "vmlinux.h"
> >  #undef hid_bpf_ctx
> > +#undef hid_report_type
> > +#undef hid_class_request
> > +#undef hid_bpf_attach_flags
> >
> >  #include <bpf/bpf_helpers.h>
> >  #include <bpf/bpf_tracing.h>
> > +#include <linux/const.h>
> >
> > +enum hid_report_type {
> > +     HID_INPUT_REPORT                = 0,
> > +     HID_OUTPUT_REPORT               = 1,
> > +     HID_FEATURE_REPORT              = 2,
> > +
> > +     HID_REPORT_TYPES,
> > +};
> >
> >  struct hid_bpf_ctx {
> >       __u32 index;
> > @@ -25,6 +39,21 @@ struct hid_bpf_ctx {
> >       };
> >  };
>
> Note, vmlinux.h has the following preamble/postamble:
>
>     #ifndef BPF_NO_PRESERVE_ACCESS_INDEX
>     #pragma clang attribute push (__attribute__((preserve_access_index)), apply_to = record)
>     #endif
>     ...
>     #ifndef BPF_NO_PRESERVE_ACCESS_INDEX
>     #pragma clang attribute pop
>     #endif
>
> You might want to use it or add __attribute__((preserve_access_index))
> to structure definitions, depending on whether or not you need CO-RE
> functionality for these tests.

I have no idea whether or not CO-RE is needed for these tests or not.
My main motivation is getting these selftests building with LLVM=1
[1].

Perhaps Benjamin could provide some more insight on whether this is
needed or not and roll out a v2 containing my patch on top + any CO-RE
semantics  -- if deemed necessary.

>
> >
> > +enum hid_class_request {
> > +     HID_REQ_GET_REPORT              = 0x01,
> > +     HID_REQ_GET_IDLE                = 0x02,
> > +     HID_REQ_GET_PROTOCOL            = 0x03,
> > +     HID_REQ_SET_REPORT              = 0x09,
> > +     HID_REQ_SET_IDLE                = 0x0A,
> > +     HID_REQ_SET_PROTOCOL            = 0x0B,
> > +};
> > +
> > +enum hid_bpf_attach_flags {
> > +     HID_BPF_FLAG_NONE = 0,
> > +     HID_BPF_FLAG_INSERT_HEAD = _BITUL(0),
> > +     HID_BPF_FLAG_MAX,
> > +};
> > +
> >  /* following are kfuncs exported by HID for HID-BPF */
> >  extern __u8 *hid_bpf_get_data(struct hid_bpf_ctx *ctx,
> >                             unsigned int offset,
> > --
> > 2.42.0.rc1.204.g551eb34607-goog
> >
>

[1]: https://github.com/ClangBuiltLinux/linux/issues/1698

Thanks
Justin