Merge: bpf: Fix uninitialized values in BPF_{CORE,PROBE}_READ

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-9/-/merge_requests/7301

JIRA: https://issues.redhat.com/browse/RHEL-100278

    commit 41d4ce6
    Author: Anton Protopopov <a.s.protopopov@gmail.com>
    Date:   Fri May 2 19:30:31 2025 +0000

        bpf: Fix uninitialized values in BPF_{CORE,PROBE}_READ

        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: 792001f ("libbpf: Add user-space variants of BPF_CORE_READ() family of macros")
        Fixes: a4b09a9 ("libbpf: Add non-CO-RE variants of BPF_CORE_READ() macro family")
        Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
        Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
        Link: https://lore.kernel.org/bpf/20250502193031.3522715-1-a.s.protopopov@gmail.com

Signed-off-by: Viktor Malik <vmalik@redhat.com>

Approved-by: Jerome Marchand <jmarchan@redhat.com>
Approved-by: Gregory Bell <grbell@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: CKI GitLab Kmaint Pipeline Bot <26919896-cki-kmaint-pipeline-bot@users.noreply.gitlab.com>

Author: CKI KWF Bot

tools/lib/bpf/bpf_core_read.h

@@ -388,7 +388,13 @@ extern void *bpf_rdonly_cast(const void *obj, __u32 btf_id) __ksym __weak;
 #define ___arrow10(a, b, c, d, e, f, g, h, i, j) a->b->c->d->e->f->g->h->i->j
 #define ___arrow(...) ___apply(___arrow, ___narg(__VA_ARGS__))(__VA_ARGS__)
 
+#if defined(__clang__) && (__clang_major__ >= 19)
+#define ___type(...) __typeof_unqual__(___arrow(__VA_ARGS__))
+#elif defined(__GNUC__) && (__GNUC__ >= 14)
+#define ___type(...) __typeof_unqual__(___arrow(__VA_ARGS__))
+#else
 #define ___type(...) typeof(___arrow(__VA_ARGS__))
+#endif
 
 #define ___read(read_fn, dst, src_type, src, accessor)			    \
 	read_fn((void *)(dst), sizeof(*(dst)), &((src_type)(src))->accessor)