s390/bpf: Use bcr 0,%0 as tail call nop filler

Currently used 0x0000 filler confuses bfd disassembler, making bpftool
prog dump xlated output nearly useless. Fix by using a real instruction.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200602174555.2501389-1-iii@linux.ibm.com

diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 0f37a1b635f858f10f440c741ae3322ff51be881..f4242b894cf28c3d5156e14e8f8c520ec109e6ee 100644 (file)
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -503,7 +503,8 @@ static void bpf_jit_prologue(struct bpf_jit *jit, u32 stack_depth)
        } else {
                /* j tail_call_start: NOP if no tail calls are used */
                EMIT4_PCREL(0xa7f40000, 6);
-               _EMIT2(0);
+               /* bcr 0,%0 */
+               EMIT2(0x0700, 0, REG_0);
        }
        /* Tail calls have to skip above initialization */
        jit->tail_call_start = jit->prg;