• Michael Holzheu's avatar
    s390/bpf: implement bpf_tail_call() helper · 6651ee07
    Michael Holzheu authored
    bpf_tail_call() arguments:
     - ctx......: Context pointer
     - jmp_table: One of BPF_MAP_TYPE_PROG_ARRAY maps used as the jump table
     - index....: Index in the jump table
    In this implementation s390x JIT does stack unwinding and jumps into the
    callee program prologue. Caller and callee use the same stack.
    With this patch a tail call generates the following code on s390x:
     if (index >= array->map.max_entries)
             goto out
     000003ff8001c7e4: e31030100016   llgf    %r1,16(%r3)
     000003ff8001c7ea: ec41001fa065   clgrj   %r4,%r1,10,3ff8001c828
     if (tail_call_cnt++ > MAX_TAIL_CALL_CNT)
             goto out;
     000003ff8001c7f0: a7080001       lhi     %r0,1
     000003ff8001c7f4: eb10f25000fa   laal    %r1,%r0,592(%r15)
     000003ff8001c7fa: ec120017207f   clij    %r1,32,2,3ff8001c828
     prog = array->prog[index];
     if (prog == NULL)
             goto out;
     000003ff8001c800: eb140003000d   sllg    %r1,%r4,3
     000003ff8001c806: e31310800004   lg      %r1,128(%r3,%r1)
     000003ff8001c80c: ec18000e007d   clgij   %r1,0,8,3ff8001c828
     Restore registers before calling function
     000003ff8001c812: eb68f2980004   lmg     %r6,%r8,664(%r15)
     000003ff8001c818: ebbff2c00004   lmg     %r11,%r15,704(%r15)
     goto *(prog->bpf_func + tail_call_start);
     000003ff8001c81e: e31100200004   lg      %r1,32(%r1,%r0)
     000003ff8001c824: 47f01006       bc      15,6(%r1)
    Reviewed-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
    Signed-off-by: default avatarMichael Holzheu <holzheu@linux.vnet.ibm.com>
    Acked-by: default avatarHeiko Carstens <heiko.carstens@de.ibm.com>
    Signed-off-by: default avatarAlexei Starovoitov <ast@plumgrid.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>