Re: [PATCH bpf-next 12/16] libbpf: Allow specifying 64-bit integers in map BTF.

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Wed, Feb 7, 2024 at 5:59 PM Alexei Starovoitov
<alexei.starovoitov@gmail.com> wrote:
>
> On Wed, Feb 7, 2024 at 5:17 PM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Tue, Feb 6, 2024 at 2:05 PM Alexei Starovoitov
> > <alexei.starovoitov@gmail.com> wrote:
> > >
> > > From: Alexei Starovoitov <ast@kernel.org>
> > >
> > > __uint() macro that is used to specify map attributes like:
> > >   __uint(type, BPF_MAP_TYPE_ARRAY);
> > >   __uint(map_flags, BPF_F_MMAPABLE);
> > > is limited to 32-bit, since BTF_KIND_ARRAY has u32 "number of elements" field.
> > >
> > > Introduce __ulong() macro that allows specifying values bigger than 32-bit.
> > > In map definition "map_extra" is the only u64 field.
> > >
> > > Signed-off-by: Alexei Starovoitov <ast@kernel.org>
> > > ---
> > >  tools/lib/bpf/bpf_helpers.h |  1 +
> > >  tools/lib/bpf/libbpf.c      | 44 ++++++++++++++++++++++++++++++++++---
> > >  2 files changed, 42 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/tools/lib/bpf/bpf_helpers.h b/tools/lib/bpf/bpf_helpers.h
> > > index 9c777c21da28..fb909fc6866d 100644
> > > --- a/tools/lib/bpf/bpf_helpers.h
> > > +++ b/tools/lib/bpf/bpf_helpers.h
> > > @@ -13,6 +13,7 @@
> > >  #define __uint(name, val) int (*name)[val]
> > >  #define __type(name, val) typeof(val) *name
> > >  #define __array(name, val) typeof(val) *name[]
> > > +#define __ulong(name, val) enum name##__enum { name##__value = val } name
> >
> > Can you try using __ulong() twice in the same file? enum type and
> > value names have global visibility, so I suspect second use with the
> > same field name would cause compilation error
>
> Good point will change it to:
>
> #define __ulong(name, val) enum { __PASTE(__unique_value,__COUNTER__)
> = val } name

yep, that should work. We still can have name collisions across
multiple files, but it doesn't matter when linking two .bpf.o files.