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    sparc: bpf_jit: fix loads from negative offsets · 35607b02
    Alexei Starovoitov 提交于
    - fix BPF_LD|ABS|IND from negative offsets:
      make sure to sign extend lower 32 bits in 64-bit register
      before calling C helpers from JITed code, otherwise 'int k'
      argument of bpf_internal_load_pointer_neg_helper() function
      will be added as large unsigned integer, causing packet size
      check to trigger and abort the program.
    
      It's worth noting that JITed code for 'A = A op K' will affect
      upper 32 bits differently depending whether K is simm13 or not.
      Since small constants are sign extended, whereas large constants
      are stored in temp register and zero extended.
      That is ok and we don't have to pay a penalty of sign extension
      for every sethi, since all classic BPF instructions have 32-bit
      semantics and we only need to set correct upper bits when
      transitioning from JITed code into C.
    
    - though instructions 'A &= 0' and 'A *= 0' are odd, JIT compiler
      should not optimize them out
    Signed-off-by: NAlexei Starovoitov <ast@plumgrid.com>
    Signed-off-by: NDavid S. Miller <davem@davemloft.net>
    35607b02
bpf_jit_asm.S 4.3 KB