Commit 41d4ce6d authored by Anton Protopopov's avatar Anton Protopopov Committed by Andrii Nakryiko
Browse files

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: 792001f4 ("libbpf: Add user-space variants of BPF_CORE_READ() family of macros")
Fixes: a4b09a9e ("libbpf: Add non-CO-RE variants of BPF_CORE_READ() macro family")
Signed-off-by: default avatarAnton Protopopov <a.s.protopopov@gmail.com>
Signed-off-by: default avatarAndrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250502193031.3522715-1-a.s.protopopov@gmail.com
parent a28fe316

tools/lib/bpf/bpf_core_read.h

+6 −0
Original line number Diff line number Diff line
@@ -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)