On Thu, Sep 21, 2017 at 05:24:10PM +0100, Edward Cree 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.
> 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?
How about:
r4 = (be16) (u16) r4
r4 = (le64) (u64) r4
most C like and most explicit ?
it should be easy to grasp that (be16) cast on big-endian arch is a nop and
swap on little.
