From: Ilya Leoshkevich <iii@linux.ibm.com>
Date: Tue, 2 Jun 2020 17:45:55 +0000 (+0200)
Subject: s390/bpf: Use bcr 0,%0 as tail call nop filler
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=33d21f18204cb33b43ca6c78c8180949f6dc7227;p=linux.git

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 0f37a1b635f85..f4242b894cf28 100644
--- 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;