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.
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?
