Re: [PATCH bpf-next v2 8/9] selftests/bpf: Add selftests for load-acquire and store-release instructions

[Eduard Zingerman <eddyz87@gmail.com>]

On Fri, 2025-02-07 at 02:06 +0000, Peilin Ye wrote:
> Add several ./test_progs tests:
> 
>   - arena_atomics/load_acquire
>   - arena_atomics/store_release
>   - verifier_load_acquire/*
>   - verifier_store_release/*
>   - verifier_precision/bpf_load_acquire
>   - verifier_precision/bpf_store_release
> 
> The last two tests are added to check if backtrack_insn() handles the
> new instructions correctly.
> 
> Additionally, the last test also makes sure that the verifier
> "remembers" the value (in src_reg) we store-release into e.g. a stack
> slot.  For example, if we take a look at the test program:
> 
>     #0:  r1 = 8;
>       /* store_release((u64 *)(r10 - 8), r1); */
>     #1:  .8byte %[store_release];
>     #2:  r1 = *(u64 *)(r10 - 8);
>     #3:  r2 = r10;
>     #4:  r2 += r1;
>     #5:  r0 = 0;
>     #6:  exit;
> 
> At #1, if the verifier doesn't remember that we wrote 8 to the stack,
> then later at #4 we would be adding an unbounded scalar value to the
> stack pointer, which would cause the program to be rejected:
> 
>   VERIFIER LOG:
>   =============
> ...
>   math between fp pointer and register with unbounded min value is not allowed
> 
> All new tests depend on #ifdef ENABLE_ATOMICS_TESTS.  Currently they
> only run for arm64.
> 
> Signed-off-by: Peilin Ye <yepeilin@google.com>
> ---

Acked-by: Eduard Zingerman <eddyz87@gmail.com>

[...]

> +++ b/tools/testing/selftests/bpf/progs/verifier_load_acquire.c
> @@ -0,0 +1,190 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include "../../../include/linux/filter.h"
> +#include "bpf_misc.h"
> +
> +#if defined(ENABLE_ATOMICS_TESTS) && defined(__TARGET_ARCH_arm64)

[...]

> +#else
> +
> +SEC("socket")
> +__description("load-acquire is not supported by compiler or jit, use a dummy test")
> +__success
> +int dummy_test(void)
> +{
> +	return 0;
> +}

Nit: why is dummy_test() necessary?

> +
> +#endif
> +
> +char _license[] SEC("license") = "GPL";

[...]