netdev - Re: [PATCH v2 1/1] libbpf: replace typeof with __typeof_

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Date:   Wed, 8 Jun 2022 14:50:52 +0200
From:   Daniel Borkmann <daniel@...earbox.net>
To:     James Hilliard <james.hilliard1@...il.com>, bpf@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        Björn Töpel <bjorn@...nel.org>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jonathan Lemon <jonathan.lemon@...il.com>,
        "open list:BPF (Safe dynamic programs and tools)" 
        <netdev@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] libbpf: replace typeof with __typeof__

Hi James,

On 6/8/22 8:40 AM, James Hilliard wrote:
> It seems the gcc preprocessor breaks when typeof is used with
> macros.
> 
> Fixes errors like:
> error: expected identifier or '(' before '#pragma'
>    106 | SEC("cgroup/bind6")
>        | ^~~
> 
> error: expected '=', ',', ';', 'asm' or '__attribute__' before '#pragma'
>    114 | char _license[] SEC("license") = "GPL";
>        | ^~~
> 
> Signed-off-by: James Hilliard <james.hilliard1@...il.com>
> ---
> Changes v1 -> v2:
>    - replace typeof with __typeof__ instead of changing pragma macros
> ---
>   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(-)
> 
> diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h
> index fd48b1ff59ca..d3a88721c9e7 100644
> --- a/tools/lib/bpf/bpf_core_read.h
> +++ b/tools/lib/bpf/bpf_core_read.h
> @@ -111,7 +111,7 @@ enum bpf_enum_value_kind {
>   })
>   
>   #define ___bpf_field_ref1(field)	(field)
> -#define ___bpf_field_ref2(type, field)	(((typeof(type) *)0)->field)
> +#define ___bpf_field_ref2(type, field)	(((__typeof__(type) *)0)->field)
>   #define ___bpf_field_ref(args...)					    \
>   	___bpf_apply(___bpf_field_ref, ___bpf_narg(args))(args)
>   

Can't we just add the below?

#ifndef typeof
# define typeof __typeof__
#endif

Thanks,
Daniel