Re: [PATCH bpf v4 13/14] bpf/tests: Fix error in tail call limit tests

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On 09/14/2021 05:18 PM, Johan Almbladh wrote:
This patch fixes an error in the tail call limit test that caused the
test to fail on for x86-64 JIT. Previously, the register R0 was used to
report the total number of tail calls made. However, after a tail call
fall-through, the value of the R0 register is undefined. Now, all tail
call error path tests instead use context state to store the count.

Fixes: 874be05f525e ("bpf, tests: Add tail call test suite")
Reported-by: Paul Chaignon <paul@xxxxxxxxx>
Reported-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
Signed-off-by: Johan Almbladh <johan.almbladh@xxxxxxxxxxxxxxxxx>
---
  lib/test_bpf.c | 37 +++++++++++++++++++++++++++----------
  1 file changed, 27 insertions(+), 10 deletions(-)

diff --git a/lib/test_bpf.c b/lib/test_bpf.c
index 7475abfd2186..ddb9a8089d2e 100644
--- a/lib/test_bpf.c
+++ b/lib/test_bpf.c
@@ -12179,10 +12179,15 @@ static __init int test_bpf(void)
  struct tail_call_test {
  	const char *descr;
  	struct bpf_insn insns[MAX_INSNS];
+	int flags;
  	int result;
  	int stack_depth;
  };
+/* Flags that can be passed to tail call test cases */
+#define FLAG_NEED_STATE		BIT(0)
+#define FLAG_RESULT_IN_STATE	BIT(1)
+
  /*
   * Magic marker used in test snippets for tail calls below.
   * BPF_LD/MOV to R2 and R2 with this immediate value is replaced
@@ -12252,32 +12257,38 @@ static struct tail_call_test tail_call_tests[] = {
  	{
  		"Tail call error path, max count reached",
  		.insns = {
-			BPF_ALU64_IMM(BPF_ADD, R1, 1),
-			BPF_ALU64_REG(BPF_MOV, R0, R1),
+			BPF_LDX_MEM(BPF_W, R2, R1, 0),
+			BPF_ALU64_IMM(BPF_ADD, R2, 1),
+			BPF_STX_MEM(BPF_W, R1, R2, 0),
  			TAIL_CALL(0),
  			BPF_EXIT_INSN(),
  		},
-		.result = MAX_TAIL_CALL_CNT + 1,
+		.flags = FLAG_NEED_STATE | FLAG_RESULT_IN_STATE,
+		.result = (MAX_TAIL_CALL_CNT + 1 + 1) * MAX_TESTRUNS,

Hi Johan,

I have tested this patch,
It should be "MAX_TAIL_CALL_CNT + 1" instead of "MAX_TAIL_CALL_CNT + 1 + 1"?

[...]

Thanks,
Tiezhu




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