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

[Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>]

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.

Tested-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>

> [...]
>
> Thanks,
> Tiezhu