Only BPF functions make use of the tail call counter; helpers and
kfuncs ignore and most likely also clobber it. Writing it into these
functions' frames is pointless and misleading, so do not do it.
Fixes: dd691e847d28 ("s390/bpf: Implement bpf_jit_supports_subprog_tailcalls()")
Signed-off-by: Ilya Leoshkevich <iii@xxxxxxxxxxxxx>
---
arch/s390/net/bpf_jit_comp.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index bb17efe29d65..bfac1ddf3447 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -1790,6 +1790,7 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
REG_SET_SEEN(BPF_REG_5);
jit->seen |= SEEN_FUNC;
+
/*
* Copy the tail call counter to where the callee expects it.
*
@@ -1800,10 +1801,17 @@ static noinline int bpf_jit_insn(struct bpf_jit *jit, struct bpf_prog *fp,
* Note 2: We assume that the verifier does not let us call the
* main program, which clears the tail call counter on entry.
*/
- /* mvc tail_call_cnt(4,%r15),frame_off+tail_call_cnt(%r15) */
- _EMIT6(0xd203f000 | offsetof(struct prog_frame, tail_call_cnt),
- 0xf000 | (jit->frame_off +
- offsetof(struct prog_frame, tail_call_cnt)));
+
+ if (insn->src_reg == BPF_PSEUDO_CALL)
+ /*
+ * mvc tail_call_cnt(4,%r15),
+ * frame_off+tail_call_cnt(%r15)
+ */
+ _EMIT6(0xd203f000 | offsetof(struct prog_frame,
+ tail_call_cnt),
+ 0xf000 | (jit->frame_off +
+ offsetof(struct prog_frame,
+ tail_call_cnt)));
/* Sign-extend the kfunc arguments. */
if (insn->src_reg == BPF_PSEUDO_KFUNC_CALL) {
--
2.50.1
