On Wed, Apr 30, 2025 at 10:43 AM Anton Protopopov
<a.s.protopopov@xxxxxxxxx> wrote:
>
> With the latest LLVM bpf selftests build will fail with
> the following error message:
>
> progs/profiler.inc.h:710:31: error: default initialization of an object of type 'typeof ((parent_task)->real_cred->uid.val)' (aka 'const unsigned int') leaves the object uninitialized and is incompatible with C++ [-Werror,-Wdefault-const-init-unsafe]
> 710 | proc_exec_data->parent_uid = BPF_CORE_READ(parent_task, real_cred, uid.val);
> | ^
> tools/testing/selftests/bpf/tools/include/bpf/bpf_core_read.h:520:35: note: expanded from macro 'BPF_CORE_READ'
> 520 | ___type((src), a, ##__VA_ARGS__) __r; \
> | ^
>
> This happens because BPF_CORE_READ (and other macro) declare the
> variable __r using the ___type macro which can inherit const modifier
> from intermediate types.
>
> Fix this by using __typeof_unqual__, when supported. (And when it
> is not supported, the problem shouldn't appear, as older compilers
> haven't complained.)
>
> Fixes: 792001f4f7aa ("libbpf: Add user-space variants of BPF_CORE_READ() family of macros")
> Fixes: a4b09a9ef945 ("libbpf: Add non-CO-RE variants of BPF_CORE_READ() macro family")
> Signed-off-by: Anton Protopopov <a.s.protopopov@xxxxxxxxx>
> ---
> tools/lib/bpf/bpf_core_read.h | 16 ++++++++++++----
> 1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h
> index c0e13cdf9660..a371213b7f3e 100644
> --- a/tools/lib/bpf/bpf_core_read.h
> +++ b/tools/lib/bpf/bpf_core_read.h
> @@ -390,6 +390,14 @@ extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak;
>
> #define ___type(...) typeof(___arrow(__VA_ARGS__))
>
> +#if defined(__clang__) && (__clang_major__ >= 19)
> +#define ___type_unqual(...) __typeof_unqual__(___arrow(__VA_ARGS__))
> +#elif defined(__GNUC__) && (__GNUC__ >= 14)
> +#define ___type_unqual(...) __typeof_unqual__(___arrow(__VA_ARGS__))
> +#else
> +#define ___type_unqual(...) ___type(__VA_ARGS__)
> +#endif
instead of defining both ___type_unqual and ___type, let's just define
___type as either typeof or typeof_unqual and use it uniformly? I
don't think we ever care about const/volatile/restrict stuff in
___type usage
pw-bot: cr
> +
> #define ___read(read_fn, dst, src_type, src, accessor) \
> read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor)
>
> @@ -517,7 +525,7 @@ extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak;
> * than enough for any practical purpose.
> */
> #define BPF_CORE_READ(src, a, ...) ({ \
> - ___type((src), a, ##__VA_ARGS__) __r; \
> + ___type_unqual((src), a, ##__VA_ARGS__) __r; \
> BPF_CORE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \
> __r; \
> })
> @@ -533,14 +541,14 @@ extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak;
> * input argument.
> */
> #define BPF_CORE_READ_USER(src, a, ...) ({ \
> - ___type((src), a, ##__VA_ARGS__) __r; \
> + ___type_unqual((src), a, ##__VA_ARGS__) __r; \
> BPF_CORE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \
> __r; \
> })
>
> /* Non-CO-RE variant of BPF_CORE_READ() */
> #define BPF_PROBE_READ(src, a, ...) ({ \
> - ___type((src), a, ##__VA_ARGS__) __r; \
> + ___type_unqual((src), a, ##__VA_ARGS__) __r; \
> BPF_PROBE_READ_INTO(&__r, (src), a, ##__VA_ARGS__); \
> __r; \
> })
> @@ -552,7 +560,7 @@ extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak;
> * not restricted to kernel types only.
> */
> #define BPF_PROBE_READ_USER(src, a, ...) ({ \
> - ___type((src), a, ##__VA_ARGS__) __r; \
> + ___type_unqual((src), a, ##__VA_ARGS__) __r; \
> BPF_PROBE_READ_USER_INTO(&__r, (src), a, ##__VA_ARGS__); \
> __r; \
> })
> --
> 2.34.1
>
>
