On Wed, Apr 26, 2023 at 6:25 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Wed, Apr 26, 2023 at 8:54 AM Stanislav Fomichev <sdf@xxxxxxxxxx> wrote:
> >
> > From: Peng Wei <pengweiprc@xxxxxxxxxx>
> >
> > Compiling C++ BPF programs with existing bpf_helper_defs.h is not
> > possible due to stricter C++ type conversions. C++ complains
> > about (void *) type conversions:
> >
> > $ clang++ --include linux/types.h ./tools/lib/bpf/bpf_helper_defs.h
> >
> > bpf_helper_defs.h:57:67: error: invalid conversion from ‘void*’ to ‘void* (*)(void*, const void*)’ [-fpermissive]
>
> Can you use -fpermissive instead? As Yonghong said, C++ is not really
> supported, so pretending we do will just cause more confusion and
> issues down the line.
I get the same errors with -fpermissive :-(
RE unsupported C++: we are not really subscribing to support it here, right?
Just making it easier for the folks who want to experiment with it to
try it out.
Maybe I should stick something like this into the header?
#ifdef __cplusplus
#warning "C++ is not supported, use at your own risk!"
#endif
But we should be able to carry this patch internally if you see no value.
I wanted to share it in case somebody else is gonna try the same eventually..
> BTW, can you elaborate more on v4 vs v6 code reuse (or what was it)? I
> wonder if there is something that would stay within C domain that
> could be done?
We have a program which handles both v4 and v6 packets. The logic is
mostly the same for v4 and v6: parse out the addresses, ports, lookup
some maps and do some action on match. Right now, both cases are
handled explicitly with a bunch of copy-paste. The idea of this c++
experiment is to leverage templates to write this logic once and
parametrize on the address sizes, packet field offsets, etc. I'm
pretty certain we can do similar things in C, but it feels like it
will be less expressive and a bit more ugly (assuming we'd use a
preprocessor to do it).
> > 57 | static void *(*bpf_map_lookup_elem)(void *map, const void *key) = (void *) 1;
> > | ^~~~~~~~~~
> > | |
> > | void*
> >
> > Extend bpf_doc.py to use proper function type instead of void.
> >
> > Before:
> > static void *(*bpf_map_lookup_elem)(void *map, const void *key) = (void *) 1;
> >
> > After:
> > static void *(*bpf_map_lookup_elem)(void *map, const void *key) = (void *(*)(void *map, const void *key)) 1;
> >
> > v2:
> > - add clang++ invocation example (Yonghong)
> >
> > Cc: Yonghong Song <yhs@xxxxxxxx>
> > Signed-off-by: Peng Wei <pengweiprc@xxxxxxxxxx>
> > Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxx>
> > ---
> > scripts/bpf_doc.py | 7 ++++++-
> > 1 file changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/scripts/bpf_doc.py b/scripts/bpf_doc.py
> > index eaae2ce78381..fa21137a90e7 100755
> > --- a/scripts/bpf_doc.py
> > +++ b/scripts/bpf_doc.py
> > @@ -827,6 +827,9 @@ COMMANDS
> > print(' *{}{}'.format(' \t' if line else '', line))
> >
> > print(' */')
> > + fptr_type = '%s%s(*)(' % (
> > + self.map_type(proto['ret_type']),
> > + ((' ' + proto['ret_star']) if proto['ret_star'] else ''))
> > print('static %s %s(*%s)(' % (self.map_type(proto['ret_type']),
> > proto['ret_star'], proto['name']), end='')
> > comma = ''
> > @@ -845,8 +848,10 @@ COMMANDS
> > one_arg += '{}'.format(n)
> > comma = ', '
> > print(one_arg, end='')
> > + fptr_type += one_arg
> >
> > - print(') = (void *) %d;' % helper.enum_val)
> > + fptr_type += ')'
> > + print(') = (%s) %d;' % (fptr_type, helper.enum_val))
> > print('')
> >
> > ###############################################################################
> > --
> > 2.40.1.495.gc816e09b53d-goog
> >
