On Tue, Sep 14, 2021 at 2:55 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
>
> On 09/14/2021 08:41 PM, Tiezhu Yang wrote:
> > 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"?
>
> Oh, sorry, it is right when MAX_TAIL_CALL_CNT is 32,
> I have tested it based on MAX_TAIL_CALL_CNT is 33,
> so I need to modify here if MAX_TAIL_CALL_CNT is 33 in my v3 patch.
No worries! I wrote it that way to indicate that there are two +1s.
The first is from the behaviour that actual count (33) = configured
count (32) + 1. The second is for the initial BPF program call, which
increments the counter but is not in itself a tail call.
>
> Tested-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
Thanks!
Johan
>
> >
> > [...]
> >
> > Thanks,
> > Tiezhu
>
