On Thu, Sep 21, 2017 at 9:24 AM, Edward Cree <ec...@solarflare.com> wrote:
> On 21/09/17 16:52, Alexei Starovoitov wrote:
>> On Thu, Sep 21, 2017 at 04:09:34PM +0100, Edward Cree wrote:
>>> print_bpf_insn() was treating all BPF_ALU[64] the same, but BPF_END has a
>>> different structure: it has a size in insn->imm (even if it's BPF_X) and
>>> uses the BPF_SRC (X or K) to indicate which endianness to use. So it
>>> needs different code to print it.
>>>
>>> Signed-off-by: Edward Cree <ec...@solarflare.com>
>>> ---
>>> It's not the same format as the new LLVM asm uses, does that matter?
>>> AFAIK the LLVM format doesn't comprehend BPF_TO_LE, just assumes that all
>>> endian ops are necessarily swaps (rather than sometimes nops).
>> that is being fixed and we will fix asm format too.
>> Let's pick good format first.
> Agreed.
>>> kernel/bpf/verifier.c | 13 +++++++++++--
>>> 1 file changed, 11 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
>>> index 799b245..e7657a4 100644
>>> --- a/kernel/bpf/verifier.c
>>> +++ b/kernel/bpf/verifier.c
>>> @@ -331,20 +331,29 @@ static void print_bpf_insn(const struct
>>> bpf_verifier_env *env,
>>> u8 class = BPF_CLASS(insn->code);
>>>
>>> if (class == BPF_ALU || class == BPF_ALU64) {
>>> - if (BPF_SRC(insn->code) == BPF_X)
>>> + if (BPF_OP(insn->code) == BPF_END) {
>>> + if (class == BPF_ALU64)
>>> + verbose("BUG_alu64_%02x\n", insn->code);
>>> + else
>>> + verbose("(%02x) (u%d) r%d %s %s\n",
>>> + insn->code, insn->imm, insn->dst_reg,
>>> + bpf_alu_string[BPF_END >> 4],
>>> + BPF_SRC(insn->code) == BPF_X ? "be" :
>>> "le");
>> yes the bit the same, but please use BPF_SRC(insn->code) == BPF_TO_BE.
> Good point.
>> imo
>> (u16) r4 endian be
>> isn't intuitive.
>> Can we come up with some better syntax?
>> Like
>> bswap16be r4
>> bswap32le r4
> Hmm, I don't like these, since bswapbe is a swap on *le* and a nop on be.
>> or
>>
>> to_be16 r4
>> to_le32 r4
> And the problem here is that it's not just to_be, it's also from_be.
Could you explain what is "from_be" here? Do not quite understand.
> Otherwise we could write `(be16) r4 = endian (u16) r4` and be much more
> explicit about what's happening.
> Really the operation is something like `cpu_tofrom_be16 r4`, but that also
> seems a bit clumsy and longwinded. Also it's inconsistent with the other
> ops that all indicate sizes with these (u16) etc casts.
> `endian (be16) r4`, perhaps?
