Re: [PATCH 1/1] libbpf: replace typeof with __typeof__ for -std=c17 compatibility

[James Hilliard]

On Thu, Jun 9, 2022 at 12:11 PM Andrii Nakryiko
<andrii.nakryiko@xxxxxxxxx> wrote:
>
> On Wed, Jun 8, 2022 at 11:28 PM James Hilliard
> <james.hilliard1@xxxxxxxxx> wrote:
> >
> > Fixes errors like:
> > error: expected specifier-qualifier-list before 'typeof'
> >    14 | #define __type(name, val) typeof(val) *name
> >       |                           ^~~~~~
> > ../src/core/bpf/socket_bind/socket-bind.bpf.c:25:9: note: in expansion of macro '__type'
> >    25 |         __type(key, __u32);
> >       |         ^~~~~~
> >
> > Signed-off-by: James Hilliard <james.hilliard1@xxxxxxxxx>
> > ---
>
> If you follow DPDK link you gave me ([0]), you'll see that they ended up doing
>
> #ifndef typeof
> #define typeof __typeof__
> #endif
>
> It's way more localized. Let's do that.

Won't that potentially leak the redefinition into external code including the
header file?

I don't see a redefinition of typeof like that used elsewhere in the kernel.

However I do see __typeof__ used in many headers already so that approach
seems to follow normal conventions and seems less risky.

FYI using -std=gnu17 instead of -std=c17 works around this issue with bpf-gcc
at least so this issue isn't really a blocker like the SEC macro
issue, I had just
accidentally mixed the two issues up due to accidentally not clearing out some
header files when testing, they seem to be entirely separate.

>
> But also I tried to build libbpf-bootstrap with -std=c17 and
> immediately ran into issue with asm, so we need to do the same with
> asm -> __asm__. Can you please update your patch and fix both issues?

Are you hitting that with clang/llvm or bpf-gcc? It doesn't appear that the
libbpf-bootstrap build system is set up to build with bpf-gcc yet.

>
>   [0] https://patches.dpdk.org/project/dpdk/patch/2601191342CEEE43887BDE71AB977258213F3012@xxxxxxxxxxxxxxxxxxxxxxxxxxxx/
>   [1] https://github.com/libbpf/libbpf-bootstrap
>
>
> >  tools/lib/bpf/bpf_core_read.h   | 16 ++++++++--------
> >  tools/lib/bpf/bpf_helpers.h     |  4 ++--
> >  tools/lib/bpf/bpf_tracing.h     | 24 ++++++++++++------------
> >  tools/lib/bpf/btf.h             |  4 ++--
> >  tools/lib/bpf/libbpf_internal.h |  6 +++---
> >  tools/lib/bpf/usdt.bpf.h        |  6 +++---
> >  tools/lib/bpf/xsk.h             | 12 ++++++------
> >  7 files changed, 36 insertions(+), 36 deletions(-)
> >
>
> [...]