s390/bpf: implement bpf_tail_call() helper
authorMichael Holzheu <holzheu@linux.vnet.ibm.com>
Tue, 9 Jun 2015 04:51:06 +0000 (21:51 -0700)
committerDavid S. Miller <davem@davemloft.net>
Tue, 9 Jun 2015 18:47:10 +0000 (11:47 -0700)
commit6651ee070b3124fe9b9db383e3a895a0e4aded65
treecd1662179dd84ff08d76eb85037900538540c3fc
parent941742f49762ba4c908510f036b09a46c1b14513
s390/bpf: implement bpf_tail_call() helper

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
 000003ff8001c7e4e31030100016   llgf    %r1,16(%r3)
 000003ff8001c7eaec41001fa065   clgrj   %r4,%r1,10,3ff8001c828

 if (tail_call_cnt++ > MAX_TAIL_CALL_CNT)
         goto out;
 000003ff8001c7f0a7080001       lhi     %r0,1
 000003ff8001c7f4eb10f25000fa   laal    %r1,%r0,592(%r15)
 000003ff8001c7faec120017207f   clij    %r1,32,2,3ff8001c828

 prog = array->prog[index];
 if (prog == NULL)
         goto out;
 000003ff8001c800eb140003000d   sllg    %r1,%r4,3
 000003ff8001c806e31310800004   lg      %r1,128(%r3,%r1)
 000003ff8001c80cec18000e007d   clgij   %r1,0,8,3ff8001c828

 Restore registers before calling function
 000003ff8001c812eb68f2980004   lmg     %r6,%r8,664(%r15)
 000003ff8001c818ebbff2c00004   lmg     %r11,%r15,704(%r15)

 goto *(prog->bpf_func + tail_call_start);
 000003ff8001c81ee31100200004   lg      %r1,32(%r1,%r0)
 000003ff8001c82447f01006       bc      15,6(%r1)

Reviewed-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Michael Holzheu <holzheu@linux.vnet.ibm.com>
Acked-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
arch/s390/net/bpf_jit.h
arch/s390/net/bpf_jit_comp.c