netdev - Re: [PATCH v2 bpf-next 1/3] bpf: switch BPF UAPI #define constants to enums

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Date:   Mon, 2 Mar 2020 08:22:11 -0800
From:   Yonghong Song <yhs@...com>
To:     Andrii Nakryiko <andriin@...com>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, <ast@...com>, <daniel@...earbox.net>
CC:     <andrii.nakryiko@...il.com>, <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 1/3] bpf: switch BPF UAPI #define constants to
 enums



On 2/29/20 10:24 PM, Andrii Nakryiko wrote:
> Switch BPF UAPI constants, previously defined as #define macro, to anonymous
> enum values. This preserves constants values and behavior in expressions, but
> has added advantaged of being captured as part of DWARF and, subsequently, BTF
> type info. Which, in turn, greatly improves usefulness of generated vmlinux.h
> for BPF applications, as it will not require BPF users to copy/paste various
> flags and constants, which are frequently used with BPF helpers.
> 
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>   include/uapi/linux/bpf.h              | 272 +++++++++++++++----------
>   include/uapi/linux/bpf_common.h       |  86 ++++----
>   include/uapi/linux/btf.h              |  60 +++---
>   tools/include/uapi/linux/bpf.h        | 274 ++++++++++++++++----------
>   tools/include/uapi/linux/bpf_common.h |  86 ++++----
>   tools/include/uapi/linux/btf.h        |  60 +++---
>   6 files changed, 497 insertions(+), 341 deletions(-)
> 
> diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
> index 8e98ced0963b..03e08f256bd1 100644
> --- a/include/uapi/linux/bpf.h
> +++ b/include/uapi/linux/bpf.h
> @@ -14,34 +14,36 @@
>   /* Extended instruction set based on top of classic BPF */
>   
>   /* instruction classes */
> -#define BPF_JMP32	0x06	/* jmp mode in word width */
> -#define BPF_ALU64	0x07	/* alu mode in double word width */
> +enum {
> +	BPF_JMP32	= 0x06,	/* jmp mode in word width */
> +	BPF_ALU64	= 0x07,	/* alu mode in double word width */

Not sure whether we have uapi backward compatibility or not.
One possibility is to add
   #define BPF_ALU64 BPF_ALU64
this way, people uses macros will continue to work.

If this is an acceptable solution, we have a lot of constants
in net related headers and will benefit from this conversion for
kprobe/tracepoint of networking related functions.

>   
>   /* ld/ldx fields */
> -#define BPF_DW		0x18	/* double word (64-bit) */
> -#define BPF_XADD	0xc0	/* exclusive add */
> +	BPF_DW		= 0x18,	/* double word (64-bit) */
> +	BPF_XADD	= 0xc0,	/* exclusive add */
>   
>   /* alu/jmp fields */
> -#define BPF_MOV		0xb0	/* mov reg to reg */
> -#define BPF_ARSH	0xc0	/* sign extending arithmetic shift right */
> +	BPF_MOV		= 0xb0,	/* mov reg to reg */
> +	BPF_ARSH	= 0xc0,	/* sign extending arithmetic shift right */
>   
>   /* change endianness of a register */
> -#define BPF_END		0xd0	/* flags for endianness conversion: */
> -#define BPF_TO_LE	0x00	/* convert to little-endian */
> -#define BPF_TO_BE	0x08	/* convert to big-endian */
> -#define BPF_FROM_LE	BPF_TO_LE
> -#define BPF_FROM_BE	BPF_TO_BE
> +	BPF_END		= 0xd0,	/* flags for endianness conversion: */
> +	BPF_TO_LE	= 0x00,	/* convert to little-endian */
> +	BPF_TO_BE	= 0x08,	/* convert to big-endian */
> +	BPF_FROM_LE	= BPF_TO_LE,
> +	BPF_FROM_BE	= BPF_TO_BE,
>   
>   /* jmp encodings */
> -#define BPF_JNE		0x50	/* jump != */
> -#define BPF_JLT		0xa0	/* LT is unsigned, '<' */
> -#define BPF_JLE		0xb0	/* LE is unsigned, '<=' */
> -#define BPF_JSGT	0x60	/* SGT is signed '>', GT in x86 */
> -#define BPF_JSGE	0x70	/* SGE is signed '>=', GE in x86 */
> -#define BPF_JSLT	0xc0	/* SLT is signed, '<' */
> -#define BPF_JSLE	0xd0	/* SLE is signed, '<=' */
> -#define BPF_CALL	0x80	/* function call */
> -#define BPF_EXIT	0x90	/* function return */
> +	BPF_JNE		= 0x50,	/* jump != */
> +	BPF_JLT		= 0xa0,	/* LT is unsigned, '<' */
> +	BPF_JLE		= 0xb0,	/* LE is unsigned, '<=' */
> +	BPF_JSGT	= 0x60,	/* SGT is signed '>', GT in x86 */
> +	BPF_JSGE	= 0x70,	/* SGE is signed '>=', GE in x86 */
> +	BPF_JSLT	= 0xc0,	/* SLT is signed, '<' */
> +	BPF_JSLE	= 0xd0,	/* SLE is signed, '<=' */
> +	BPF_CALL	= 0x80,	/* function call */
> +	BPF_EXIT	= 0x90,	/* function return */
> +};
>   
[...]