• Eric Dumazet's avatar
    net: filter: Just In Time compiler for x86-64 · 0a14842f
    Eric Dumazet authored
    
    
    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: default avatarEric Dumazet <eric.dumazet@gmail.com>
    Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
    Cc: Ben Hutchings <bhutchings@solarflare.com>
    Cc: Hagen Paul Pfeifer <hagen@jauu.net>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    0a14842f