Re: [RFC PATCH bpf-next v5 2/2] net: Add additional bit to support clockid_t timestamp type

[Martin KaFai Lau <martin.lau@linux.dev>]

On 5/3/24 2:33 PM, Abhishek Chauhan (ABC) wrote:
> 
>> BPF_CALL_3(bpf_skb_set_tstamp, struct sk_buff *, skb,
>>             u64, tstamp, u32, tstamp_type)
>> {
>>      /* ... */
>>      case BPF_SKB_CLOCK_TAI:
>>          if (!tstamp)
>>              return -EINVAL;
>>          skb->tstamp = tstamp;
>>          skb->tstamp_type = SKB_CLOCK_TAI;
>>          break;
>>          case BPF_SKB_CLOCK_REALTIME:
>>          skb->tstamp = tstamp;
>>          skb->tstamp_type = SKB_CLOCK_REALTIME;
>>          break;
>>
>>      /* ... */
>> }
>>
>>>                return -EINVAL;
>>
>>> @@ -9388,17 +9394,17 @@ static struct bpf_insn *bpf_convert_tstamp_type_read(const struct bpf_insn *si,
>>>    {
>>>        __u8 value_reg = si->dst_reg;
>>>        __u8 skb_reg = si->src_reg;
>>> -    /* AX is needed because src_reg and dst_reg could be the same */
>>> -    __u8 tmp_reg = BPF_REG_AX;
>>> -
>>> -    *insn++ = BPF_LDX_MEM(BPF_B, tmp_reg, skb_reg,
>>> -                  SKB_BF_MONO_TC_OFFSET);
>>> -    *insn++ = BPF_JMP32_IMM(BPF_JSET, tmp_reg,
>>> -                SKB_MONO_DELIVERY_TIME_MASK, 2);
>>> -    *insn++ = BPF_MOV32_IMM(value_reg, BPF_SKB_TSTAMP_UNSPEC);
>>> -    *insn++ = BPF_JMP_A(1);
>>> -    *insn++ = BPF_MOV32_IMM(value_reg, BPF_SKB_TSTAMP_DELIVERY_MONO);
>>> -
>>> +    BUILD_BUG_ON(__SKB_CLOCK_MAX != BPF_SKB_TSTAMP_DELIVERY_TAI);
>>
>> Add these also:
>>
>>      BUILD_BUG_ON(SKB_CLOCK_REALTIME != BPF_SKB_CLOCK_REALTIME);
>>      BUILD_BUG_ON(SKB_CLOCK_MONOTONIC != BPF_SKB_CLOCK_MONOTONIC);
>>      BUILD_BUG_ON(SKB_CLOCK_TAI != BPF_SKB_CLOCK_TAI);
>>
> 
> Martin, The above suggestion of adding BUILD_BUG_ON always gives me a warning stating the following.
> 
> Some systems considers warning as error if compiler flags are enabled. I believe this requires your suggestion before i raise RFC v6 patchset to either keep the
> BUILD_BUG_ON or remove it completely.

cast it?

> 
> /local/mnt/workspace/kernel_master/linux-next/net/core/filter.c:9395:34: warning: comparison between ‘enum skb_tstamp_type’ and ‘enum <anonymous>’ [-Wenum-compare]
>   9395 |  BUILD_BUG_ON(SKB_CLOCK_REALTIME != BPF_SKB_CLOCK_REALTIME);
>        |                                  ^~
> /local/mnt/workspace/kernel_master/linux-next/include/linux/compiler_types.h:451:9: note: in definition of macro ‘__compiletime_assert’
>    451 |   if (!(condition))     \
>        |         ^~~~~~~~~
> /local/mnt/workspace/kernel_master/linux-next/include/linux/compiler_types.h:471:2: note: in expansion of macro ‘_compiletime_assert’
>    471 |  _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
>        |  ^~~~~~~~~~~~~~~~~~~
> /local/mnt/workspace/kernel_master/linux-next/include/linux/build_bug.h:39:37: note: in expansion of macro ‘compiletime_assert’
>     39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>        |                                     ^~~~~~~~~~~~~~~~~~
> /local/mnt/workspace/kernel_master/linux-next/include/linux/build_bug.h:50:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
>     50 |  BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
>        |  ^~~~~~~~~~~~~~~~
> /local/mnt/workspace/kernel_master/linux-next/net/core/filter.c:9395:2: note: in expansion of macro ‘BUILD_BUG_ON’
>   9395 |  BUILD_BUG_ON(SKB_CLOCK_REALTIME != BPF_SKB_CLOCK_REALTIME);
>        |  ^~~~~~~~~~~~
> /local/mnt/workspace/kernel_master/linux-next/net/core/filter.c:9396:35: warning: comparison between ‘enum skb_tstamp_type’ and ‘enum <anonymous>’ [-Wenum-compare]
>   9396 |  BUILD_BUG_ON(SKB_CLOCK_MONOTONIC != BPF_SKB_CLOCK_MONOTONIC);
>        |                                   ^~
> /local/mnt/workspace/kernel_master/linux-next/include/linux/compiler_types.h:451:9: note: in definition of macro ‘__compiletime_assert’
>    451 |   if (!(condition))     \
>        |         ^~~~~~~~~
> 
>           |                                      ^~
> 
> 
>