On Wed, 2021-09-08 at 00:23 +0200, Johan Almbladh wrote:
> This patch adds a tail call limit test where the program also emits
> a BPF_CALL to an external function prior to the tail call. Mainly
> testing that JITed programs preserve its internal register state, for
> example tail call count, across such external calls.
>
> Signed-off-by: Johan Almbladh <johan.almbladh@xxxxxxxxxxxxxxxxx>
> ---
> lib/test_bpf.c | 51 +++++++++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 48 insertions(+), 3 deletions(-)
>
> diff --git a/lib/test_bpf.c b/lib/test_bpf.c
> index 7475abfd2186..6e45b4da9841 100644
> --- a/lib/test_bpf.c
> +++ b/lib/test_bpf.c
> @@ -12259,6 +12259,20 @@ static struct tail_call_test tail_call_tests[]
> = {
> },
> .result = MAX_TAIL_CALL_CNT + 1,
> },
> + {
> + "Tail call count preserved across function calls",
> + .insns = {
> + BPF_ALU64_IMM(BPF_ADD, R1, 1),
> + BPF_STX_MEM(BPF_DW, R10, R1, -8),
> + BPF_CALL_REL(0),
> + BPF_LDX_MEM(BPF_DW, R1, R10, -8),
> + BPF_ALU32_REG(BPF_MOV, R0, R1),
> + TAIL_CALL(0),
> + BPF_EXIT_INSN(),
> + },
> + .stack_depth = 8,
> + .result = MAX_TAIL_CALL_CNT + 1,
> + },
> {
> "Tail call error path, NULL target",
> .insns = {
There seems to be a problem with BPF_CALL_REL(0) on s390, since it
assumes that test_bpf_func and __bpf_call_base are within +-2G of
each other, which is not (yet) the case.
I can't think of a good fix, so how about something like this?
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -12257,6 +12257,7 @@ static struct tail_call_test tail_call_tests[]
= {
},
.result = MAX_TAIL_CALL_CNT + 1,
},
+#ifndef __s390__
{
"Tail call count preserved across function calls",
.insns = {
@@ -12271,6 +12272,7 @@ static struct tail_call_test tail_call_tests[]
= {
.stack_depth = 8,
.result = MAX_TAIL_CALL_CNT + 1,
},
+#endif
{
"Tail call error path, NULL target",
.insns = {
[...]
