Re: [PATCH bpf-next v2 13/13] bpf/tests: Add tail call limit test with external function call
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From: Ilya Leoshkevich <iii@linux.ibm.com>
Date: 2021-09-08 10:10:25
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bpf
On Wed, 2021-09-08 at 00:23 +0200, Johan Almbladh wrote:
quoted hunk ↗ jump to hunk
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@anyfinetworks.com> --- 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 = {
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