• Alexei Starovoitov's avatar
    net: filter: cleanup A/X name usage · e430f34e
    Alexei Starovoitov authored
    The macro 'A' used in internal BPF interpreter:
     #define A regs[insn->a_reg]
    was easily confused with the name of classic BPF register 'A', since
    'A' would mean two different things depending on context.
    
    This patch is trying to clean up the naming and clarify its usage in the
    following way:
    
    - A and X are names of two classic BPF registers
    
    - BPF_REG_A denotes internal BPF register R0 used to map classic register A
      in internal BPF programs generated from classic
    
    - BPF_REG_X denotes internal BPF register R7 used to map classic register X
      in internal BPF programs generated from classic
    
    - internal BPF instruction format:
    struct sock_filter_int {
            __u8    code;           /* opcode */
            __u8    dst_reg:4;      /* dest register */
            __u8    src_reg:4;      /* source register */
            __s16   off;            /* signed offset */
            __s32   imm;            /* signed immediate constant */
    };
    
    - BPF_X/BPF_K is 1 bit used to encode source operand of instruction
    In classic:
      BPF_X - means use register X as source operand
      BPF_K - means use 32-bit immediate as source operand
    In internal:
      BPF_X - means use 'src_reg' register as source operand
      BPF_K - means use 32-bit immediate as source operand
    Suggested-by: default avatarChema Gonzalez <chema@google.com>
    Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
    Acked-by: default avatarDaniel Borkmann <dborkman@redhat.com>
    Acked-by: default avatarChema Gonzalez <chema@google.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    e430f34e
bpf_jit_comp.c 25 KB