20 Dec, 2011

1 commit

• a03ffcf87   net: bpf_jit: fix an off-one bug in x86_64 cond jump target ... Browse Code »

  1

  x86 jump instruction size is 2 or 5 bytes (near/long jump), not 2 or 6
  bytes.

  In case a conditional jump is followed by a long jump, conditional jump
  target is one byte past the start of target instruction.

  Signed-off-by: Markus Kötter
  Signed-off-by: Eric Dumazet
  Signed-off-by: David S. Miller

  Markus Kötter

  2011-12-20 04:47:29 +0800  

28 Apr, 2011

1 commit

• 0a14842f5   net: filter: Just In Time compiler for x86-64 ... Browse Code »

  In order to speedup packet filtering, here is an implementation of a
  JIT compiler for x86_64

  It is disabled by default, and must be enabled by the admin.

  echo 1 >/proc/sys/net/core/bpf_jit_enable

  It uses module_alloc() and module_free() to get memory in the 2GB text
  kernel range since we call helpers functions from the generated code.

  EAX : BPF A accumulator
  EBX : BPF X accumulator
  RDI : pointer to skb (first argument given to JIT function)
  RBP : frame pointer (even if CONFIG_FRAME_POINTER=n)
  r9d : skb->len - skb->data_len (headlen)
  r8 : skb->data

  To get a trace of generated code, use :

  echo 2 >/proc/sys/net/core/bpf_jit_enable

  Example of generated code :

  # tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24

  flen=18 proglen=147 pass=3 image=ffffffffa00b5000
  JIT code: ffffffffa00b5000: 55 48 89 e5 48 83 ec 60 48 89 5d f8 44 8b 4f 60
  JIT code: ffffffffa00b5010: 44 2b 4f 64 4c 8b 87 b8 00 00 00 be 0c 00 00 00
  JIT code: ffffffffa00b5020: e8 24 7b f7 e0 3d 00 08 00 00 75 28 be 1a 00 00
  JIT code: ffffffffa00b5030: 00 e8 fe 7a f7 e0 24 00 3d 00 14 a8 c0 74 49 be
  JIT code: ffffffffa00b5040: 1e 00 00 00 e8 eb 7a f7 e0 24 00 3d 00 14 a8 c0
  JIT code: ffffffffa00b5050: 74 36 eb 3b 3d 06 08 00 00 74 07 3d 35 80 00 00
  JIT code: ffffffffa00b5060: 75 2d be 1c 00 00 00 e8 c8 7a f7 e0 24 00 3d 00
  JIT code: ffffffffa00b5070: 14 a8 c0 74 13 be 26 00 00 00 e8 b5 7a f7 e0 24
  JIT code: ffffffffa00b5080: 00 3d 00 14 a8 c0 75 07 b8 ff ff 00 00 eb 02 31
  JIT code: ffffffffa00b5090: c0 c9 c3

  BPF program is 144 bytes long, so native program is almost same size ;)

  (000) ldh [12]
  (001) jeq #0x800 jt 2 jf 8
  (002) ld [26]
  (003) and #0xffffff00
  (004) jeq #0xc0a81400 jt 16 jf 5
  (005) ld [30]
  (006) and #0xffffff00
  (007) jeq #0xc0a81400 jt 16 jf 17
  (008) jeq #0x806 jt 10 jf 9
  (009) jeq #0x8035 jt 10 jf 17
  (010) ld [28]
  (011) and #0xffffff00
  (012) jeq #0xc0a81400 jt 16 jf 13
  (013) ld [38]
  (014) and #0xffffff00
  (015) jeq #0xc0a81400 jt 16 jf 17
  (016) ret #65535
  (017) ret #0

  Signed-off-by: Eric Dumazet
  Cc: Arnaldo Carvalho de Melo
  Cc: Ben Hutchings
  Cc: Hagen Paul Pfeifer
  Signed-off-by: David S. Miller

  Eric Dumazet

  2011-04-28 14:05:08 +0800