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Date: Mon, 2 Mar 2020 10:33:19 -0800
From: Yonghong Song <yhs@...com>
To: Andrii Nakryiko <andrii.nakryiko@...il.com>
CC: Andrii Nakryiko <andriin@...com>, bpf <bpf@...r.kernel.org>,
Networking <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...com>,
Daniel Borkmann <daniel@...earbox.net>,
Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v2 bpf-next 1/3] bpf: switch BPF UAPI #define constants to
enums
On 3/2/20 10:25 AM, Andrii Nakryiko wrote:
> On Mon, Mar 2, 2020 at 8:22 AM Yonghong Song <yhs@...com> wrote:
>>
>>
>>
>> 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.
>
> This is going to be a really ugly solution, though. I wonder if it was
> ever an expected behavior of UAPI constants to be able to do #ifdef on
> them.
>
> Do you know any existing application that relies on those constants
> being #defines?
I did not have enough experience to work with system level applications.
But in linux/in.h we have
#if __UAPI_DEF_IN_IPPROTO
/* Standard well-defined IP protocols. */
enum {
IPPROTO_IP = 0, /* Dummy protocol for TCP */
#define IPPROTO_IP IPPROTO_IP
IPPROTO_ICMP = 1, /* Internet Control Message Protocol */
#define IPPROTO_ICMP IPPROTO_ICMP
IPPROTO_IGMP = 2, /* Internet Group Management Protocol */
#define IPPROTO_IGMP IPPROTO_IGMP
IPPROTO_IPIP = 4, /* IPIP tunnels (older KA9Q tunnels use
94) */
#define IPPROTO_IPIP IPPROTO_IPIP
IPPROTO_TCP = 6, /* Transmission Control Protocol */
#define IPPROTO_TCP IPPROTO_TCP
IPPROTO_EGP = 8, /* Exterior Gateway Protocol */
#define IPPROTO_EGP IPPROTO_EGP
IPPROTO_PUP = 12, /* PUP protocol */
#define IPPROTO_PUP IPPROTO_PUP
IPPROTO_UDP = 17, /* User Datagram Protocol */
#define IPPROTO_UDP IPPROTO_UDP
IPPROTO_IDP = 22, /* XNS IDP protocol */
#define IPPROTO_IDP IPPROTO_IDP
...
>
>>
>> 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 */
>>> +};
>>>
>> [...]
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