On 08/30/2016 10:48 PM, Alexei Starovoitov wrote:
On Tue, Aug 30, 2016 at 10:22:46PM +0200, Jakub Kicinski wrote:
On Tue, 30 Aug 2016 21:07:50 +0200, Daniel Borkmann wrote:
Having two modes seems more straight forward and I think we would only
need to pay attention in the LD_IMM64 case, I don't think I've seen
LLVM generating XORs, it's just the cBPF -> eBPF conversion.
Okay, though, I think that the cBPF to eBPF migration wouldn't even
pass through the bpf_parse() handling, since verifier is not aware on
some of their aspects such as emitting calls directly (w/o *proto) or
arg mappings. Probably make sense to reject these (bpf_prog_was_classic())
if they cannot be handled anyway?
TBH again I only use cBPF for testing. It's a convenient way of
generating certain instruction sequences. I can probably just drop
it completely but the XOR patch is just 3 lines of code so not a huge
cost either... I'll keep patch 6 in my tree for now.
if xor matching is only need for classic, I would drop that patch
just to avoid unnecessary state collection. The number of lines
is not a concern, but extra state for state prunning is.
Alternatively - is there any eBPF assembler out there? Something
converting verifier output back into ELF would be quite cool.
would certainly be nice. I don't think there is anything standalone.
btw llvm can be made to work as assembler only, but simple flex/bison
is probably better.
Never tried it out, but seems llvm backend doesn't have asm parser
implemented?
$ clang -target bpf -O2 -c foo.c -S -o foo.S
$ llvm-mc -arch bpf foo.S -filetype=obj -o foo.o
llvm-mc: error: this target does not support assembly parsing.
LLVM IR might work, but maybe too high level(?); alternatively, we could
make bpf_asm from tools/net/ eBPF aware for debugging purposes. If you
have a toolchain supporting libbfd et al, you could probably make use
of bpf_jit_dump() (like JITs do) and then bpf_jit_disasm tool (from
same dir as bpf_asm).
