• Daniel Borkmann's avatar
    filter: add minimal BPF JIT image disassembler · e306e2c1
    Daniel Borkmann authored
    This is a minimal stand-alone user space helper, that allows for debugging or
    verification of emitted BPF JIT images. This is in particular useful for
    emitted opcode debugging, since minor bugs in the JIT compiler can be fatal.
    The disassembler is architecture generic and uses libopcodes and libbfd.
    
    How to get to the disassembly, example:
    
      1) `echo 2 > /proc/sys/net/core/bpf_jit_enable`
      2) Load a BPF filter (e.g. `tcpdump -p -n -s 0 -i eth1 host 192.168.20.0/24`)
      3) Run e.g. `bpf_jit_disasm -o` to disassemble the most recent JIT code output
    
    `bpf_jit_disasm -o` will display the related opcodes to a particular instruction
    as well. Example for x86_64:
    
    $ ./bpf_jit_disasm
    94 bytes emitted from JIT compiler (pass:3, flen:9)
    ffffffffa0356000 + <x>:
       0:	push   %rbp
       1:	mov    %rsp,%rbp
       4:	sub    $0x60,%rsp
       8:	mov    %rbx,-0x8(%rbp)
       c:	mov    0x68(%rdi),%r9d
      10:	sub    0x6c(%rdi),%r9d
      14:	mov    0xe0(%rdi),%r8
      1b:	mov    $0xc,%esi
      20:	callq  0xffffffffe0d01b71
      25:	cmp    $0x86dd,%eax
      2a:	jne    0x000000000000003d
      2c:	mov    $0x14,%esi
      31:	callq  0xffffffffe0d01b8d
      36:	cmp    $0x6,%eax
    [...]
      5c:	leaveq
      5d:	retq
    
    $ ./bpf_jit_disasm -o
    94 bytes emitted from JIT compiler (pass:3, flen:9)
    ffffffffa0356000 + <x>:
       0:	push   %rbp
    	55
       1:	mov    %rsp,%rbp
    	48 89 e5
       4:	sub    $0x60,%rsp
    	48 83 ec 60
       8:	mov    %rbx,-0x8(%rbp)
    	48 89 5d f8
       c:	mov    0x68(%rdi),%r9d
    	44 8b 4f 68
      10:	sub    0x6c(%rdi),%r9d
    	44 2b 4f 6c
    [...]
      5c:	leaveq
    	c9
      5d:	retq
    	c3
    Signed-off-by: 's avatarDaniel Borkmann <dborkman@redhat.com>
    Signed-off-by: 's avatarDavid S. Miller <davem@davemloft.net>
    e306e2c1
Name
Last commit
Last update
..
Makefile Loading commit data...
bpf_jit_disasm.c Loading commit data...