Re: [PATCH bpf-next v1 7/8] selftests/bpf: Add selftests for load-acquire and store-release instructions

[Peilin Ye <yepeilin@google.com>]

On Tue, Jan 28, 2025 at 05:06:03PM -0800, Eduard Zingerman wrote:
> On Sat, 2025-01-25 at 02:19 +0000, Peilin Ye wrote:
> > All new tests depend on the pre-defined __BPF_FEATURE_LOAD_ACQ_STORE_REL
> > feature macro, which implies -mcpu>=v4.
> 
> This restriction would mean that tests are skipped on BPF CI, as it
> currently runs using llvm 17 and 18. Instead, I suggest using some
> macro hiding an inline assembly as below:
> 
> 	asm volatile (".8byte %[insn];"
> 	              :
> 	              : [insn]"i"(*(long *)&(BPF_RAW_INSN(...)))
> 	              : /* correct clobbers here */);
> 
> See the usage of the __imm_insn() macro in the test suite.

I see, I'll do this in v2.

> Also, "BPF_ATOMIC loads from R%d %s is not allowed\n" and
>       "BPF_ATOMIC stores into R%d %s is not allowed\n"
> situations are not tested.

Thanks!

> > --- a/tools/testing/selftests/bpf/prog_tests/atomics.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/atomics.c
> > @@ -162,6 +162,56 @@ static void test_xchg(struct atomics_lskel *skel)
> >  	ASSERT_EQ(skel->bss->xchg32_result, 1, "xchg32_result");
> >  }
> 
> Nit: Given the tests in verifier_load_acquire.c and verifier_store_release.c
>      that use __retval annotation, are these tests really necessary?
>      (assuming that verifier_store_release.c tests are modified to read
>       stored location into r0 before exit).
> 
> > +static void test_load_acquire(struct atomics_lskel *skel)

Ah, right.  I'll drop them and modify verifier_store_release.c
accordingly.

> > --- a/tools/testing/selftests/bpf/progs/arena_atomics.c
> > +++ b/tools/testing/selftests/bpf/progs/arena_atomics.c
> [...]
> 
> > +SEC("raw_tp/sys_enter")
> > +int load_acquire(const void *ctx)
> > +{
> > +	if (pid != (bpf_get_current_pid_tgid() >> 32))
> > +		return 0;
> 
> Nit: This check is not needed, since bpf_prog_test_run_opts() is used
>      to run the tests.

Got it!

Thanks,
Peilin Ye