netdev - RE: [PATCH bpf-next 02/10] bpf: add typecast to bpf helpers to help BTF generation

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Date:   Sat, 05 Oct 2019 21:00:32 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Alexei Starovoitov <ast@...nel.org>, davem@...emloft.net
Cc:     daniel@...earbox.net, x86@...nel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, kernel-team@...com
Subject: RE: [PATCH bpf-next 02/10] bpf: add typecast to bpf helpers to help
 BTF generation

Alexei Starovoitov wrote:
> When pahole converts dwarf to btf it emits only used types.
> Wrap existing bpf helper functions into typedef and use it in
> typecast to make gcc emits this type into dwarf.
> Then pahole will convert it to btf.
> The "btf_#name_of_helper" types will be used to figure out
> types of arguments of bpf helpers.
> The generate code before and after is the same.
> Only dwarf and btf are different.
> 
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  include/linux/filter.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/filter.h b/include/linux/filter.h
> index 2ce57645f3cd..d3d51d7aff2c 100644
> --- a/include/linux/filter.h
> +++ b/include/linux/filter.h
> @@ -464,10 +464,11 @@ static inline bool insn_is_zext(const struct bpf_insn *insn)
>  #define BPF_CALL_x(x, name, ...)					       \
>  	static __always_inline						       \
>  	u64 ____##name(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__));   \
> +	typedef u64 (*btf_##name)(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__)); \
>  	u64 name(__BPF_REG(x, __BPF_DECL_REGS, __BPF_N, __VA_ARGS__));	       \
>  	u64 name(__BPF_REG(x, __BPF_DECL_REGS, __BPF_N, __VA_ARGS__))	       \
>  	{								       \
> -		return ____##name(__BPF_MAP(x,__BPF_CAST,__BPF_N,__VA_ARGS__));\
> +		return ((btf_##name)____##name)(__BPF_MAP(x,__BPF_CAST,__BPF_N,__VA_ARGS__));\
>  	}								       \
>  	static __always_inline						       \
>  	u64 ____##name(__BPF_MAP(x, __BPF_DECL_ARGS, __BPF_V, __VA_ARGS__))
> -- 
> 2.20.0
> 

Acked-by: John Fastabend <john.fastabend@...il.com>