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

[Peilin Ye]

On Fri, Feb 07, 2025 at 02:06:29AM +0000, Peilin Ye wrote:
> --- a/tools/testing/selftests/bpf/progs/arena_atomics.c
> +++ b/tools/testing/selftests/bpf/progs/arena_atomics.c
> @@ -6,6 +6,8 @@
>  #include <stdbool.h>
>  #include <stdatomic.h>
>  #include "bpf_arena_common.h"
> +#include "../../../include/linux/filter.h"
> +#include "bpf_misc.h"
>  
>  struct {
>  	__uint(type, BPF_MAP_TYPE_ARENA);
> @@ -274,4 +276,90 @@ int uaf(const void *ctx)
>  	return 0;
>  }
>  
> +__u8 __arena_global load_acquire8_value = 0x12;
   ~~~~

CI job x86_64-llvm-17 [1] failed because clang-17 crashed when compiling
this file (arena_atomics.c):

  fatal error: error in backend: unable to write nop sequence of 1 bytes

After some digging, I believe I am hitting a known issue that Yonghong
described in [2].  Changing __u8 and __u16 variables to __u32 seems to
resolve/work around the issue:

  +__u32 __arena_global load_acquire8_value = 0x12;

Will look into it more.

[1] https://github.com/kernel-patches/bpf/actions/runs/13191887466/job/36826207612
[2] https://lore.kernel.org/bpf/d56223f9-483e-fbc1-4564-44c0858a1e3e@xxxxxxxx/

> +__u16 __arena_global load_acquire16_value = 0x1234;
> +__u32 __arena_global load_acquire32_value = 0x12345678;
> +__u64 __arena_global load_acquire64_value = 0x1234567890abcdef;
> +
> +__u8 __arena_global load_acquire8_result = 0x12;
> +__u16 __arena_global load_acquire16_result = 0x1234;
> +__u32 __arena_global load_acquire32_result = 0x12345678;
> +__u64 __arena_global load_acquire64_result = 0x1234567890abcdef;

Thanks,
Peilin Ye