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SubjectRe: [PATCH v6 bpf-next 1/3] libbpf: BTF dumper support for typed data

On Mon, 19 Jul 2021, Naresh Kamboju wrote:

> On Thu, 15 Jul 2021 at 20:46, Alan Maguire <alan.maguire@oracle.com> wrote:
> >
> > Add a BTF dumper for typed data, so that the user can dump a typed
> > version of the data provided.
>
> <trim>
>
> > diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
> > index 5dc6b517..929cf93 100644
> > --- a/tools/lib/bpf/btf_dump.c
> > +++ b/tools/lib/bpf/btf_dump.c
>
>
> Following perf build errors noticed on i386 and arm 32-bit architectures on
> linux next 20210719 tag with gcc-11.
>
> metadata:
> --------------
> git_repo: https://gitlab.com/Linaro/lkft/mirrors/next/linux-next
> git_short_log: 08076eab6fef ( Add linux-next specific files for 20210719 )
> toolchain: gcc-11
> target_arch: arm and i386
>
>
> > +static void btf_dump_int128(struct btf_dump *d,
> > + const struct btf_type *t,
> > + const void *data)
> > +{
> > + __int128 num = *(__int128 *)data;
>
>
> btf_dump.c: In function 'btf_dump_int128':
> btf_dump.c:1559:9: error: expected expression before '__int128'
> 1559 | __int128 num = *(__int128 *)data;
> | ^~~~~~~~
> btf_dump.c:1561:14: error: 'num' undeclared (first use in this function)
> 1561 | if ((num >> 64) == 0)
> | ^~~
> btf_dump.c:1561:14: note: each undeclared identifier is reported only
> once for each function it appears in
> btf_dump.c: At top level:
> btf_dump.c:1568:17: error: '__int128' is not supported on this target
> 1568 | static unsigned __int128 btf_dump_bitfield_get_data(struct btf_dump *d,
> | ^~~~~~~~
> btf_dump.c: In function 'btf_dump_bitfield_get_data':
> btf_dump.c:1576:18: error: '__int128' is not supported on this target
> 1576 | unsigned __int128 num = 0, ret;
> | ^~~~~~~~
> btf_dump.c: In function 'btf_dump_bitfield_check_zero':
> btf_dump.c:1608:9: error: expected expression before '__int128'
> 1608 | __int128 check_num;
> | ^~~~~~~~
> btf_dump.c:1610:9: error: 'check_num' undeclared (first use in this function)
> 1610 | check_num = btf_dump_bitfield_get_data(d, t, data,
> bits_offset, bit_sz);
> | ^~~~~~~~~
> btf_dump.c: In function 'btf_dump_bitfield_data':
> btf_dump.c:1622:18: error: '__int128' is not supported on this target
> 1622 | unsigned __int128 print_num;
> | ^~~~~~~~
> btf_dump.c: In function 'btf_dump_dump_type_data':
> btf_dump.c:2212:34: error: '__int128' is not supported on this target
> 2212 | unsigned __int128 print_num;
> | ^~~~~~~~
>
>

Thanks for the report Naresh! Andrii, I'm thinking the best
approach might be to remove use of int128 and have the bitfield
computations operate on a __u64 representation instead. With
that change, we would only lose the ability to handle int128
bitfields; what do you think? I hope to have something ready
shortly covering that, the non-propogation of return values
and the endianness issues with enum handling - in fact the
latter goes away if the bitfield computations are done for
64-bit values.

Thanks!

Alan

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