[PATCH AUTOSEL 6.17-6.1] bpftool: Fix -Wuninitialized-const-pointer warnings with clang >= 21

[Sasha Levin <sashal@kernel.org>]

From: Tom Stellard <tstellar@redhat.com>

[ Upstream commit 5612ea8b554375d45c14cbb0f8ea93ec5d172891 ]

This fixes the build with -Werror -Wall.

btf_dumper.c:71:31: error: variable 'finfo' is uninitialized when passed as a const pointer argument here [-Werror,-Wuninitialized-const-pointer]
   71 |         info.func_info = ptr_to_u64(&finfo);
      |                                      ^~~~~

prog.c:2294:31: error: variable 'func_info' is uninitialized when passed as a const pointer argument here [-Werror,-Wuninitialized-const-pointer]
 2294 |         info.func_info = ptr_to_u64(&func_info);
      |

v2:
  - Initialize instead of using memset.

Signed-off-by: Tom Stellard <tstellar@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Quentin Monnet <qmo@kernel.org>
Link: https://lore.kernel.org/bpf/20250917183847.318163-1-tstellar@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES

**Rationale**
- Fixes a real build failure with modern toolchains: clang ≥ 21 warns
  about passing the address of an uninitialized object to a function
  taking a const pointer; with `-Werror -Wall` this breaks bpftool
  builds.
- Change is minimal, localized, and non-functional: it only zero-
  initializes two local `struct bpf_func_info` instances so the address
  isn’t of an uninitialized object.
- Consistent with existing code in the same tool: other bpftool paths
  already initialize `bpf_func_info` similarly, so this aligns style and
  avoids surprises.

**Code References**
- In `tools/bpf/bpftool/btf_dumper.c:41`, `struct bpf_func_info finfo;`
  is currently uninitialized but its address is passed to `ptr_to_u64()`
  at `tools/bpf/bpftool/btf_dumper.c:71`, which triggers clang’s
  `-Wuninitialized-const-pointer`. The patch changes the declaration to
  `struct bpf_func_info finfo = {};`, preventing the warning.
- In `tools/bpf/bpftool/prog.c:2265`, `struct bpf_func_info func_info;`
  is uninitialized, and its address is passed to `ptr_to_u64()` at
  `tools/bpf/bpftool/prog.c:2294`. The patch changes the declaration to
  `struct bpf_func_info func_info = {};`, removing the warning.
- `ptr_to_u64()` is declared as taking a `const void *`
  (`tools/bpf/bpftool/main.h:25`), which is why clang applies the const-
  pointer uninitialized check when the address of an uninitialized
  object is passed.
- A precedent in the same codebase already initializes the same type:
  `tools/bpf/bpftool/common.c:416` uses `struct bpf_func_info finfo =
  {};`, demonstrating this is the established and safe pattern.

**Why It’s Safe**
- The variables are used strictly as output buffers for
  `bpf_prog_get_info_by_fd()`:
  - `btf_dumper.c`: Only after `info.nr_func_info` is non-zero and the
    second `bpf_prog_get_info_by_fd()` succeeds do we read
    `finfo.type_id` (`tools/bpf/bpftool/btf_dumper.c:80`). On error
    paths we don’t read `finfo`.
  - `prog.c`: We check `info.nr_func_info != 0` before issuing the
    second `bpf_prog_get_info_by_fd()`, and only on success read
    `func_info.type_id` (`tools/bpf/bpftool/prog.c:2308`).
- Zero-initialization does not change runtime semantics; the kernel
  overwrites these structures on success, and on failure paths they
  aren’t consumed.

**Stable Backport Criteria**
- Important bugfix: restores bpftool buildability with clang ≥ 21 under
  `-Werror -Wall`.
- Small and contained: two initializations; no ABI or behavioral
  changes.
- No architectural changes; no risk to core kernel subsystems (user-
  space tools only).
- Low regression risk; aligns with existing initialization pattern
  already present elsewhere in bpftool.

Given the above, this commit is an excellent candidate for stable
backport to keep tools building with current compilers and to maintain
consistency within bpftool.

 tools/bpf/bpftool/btf_dumper.c | 2 +-
 tools/bpf/bpftool/prog.c       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/tools/bpf/bpftool/btf_dumper.c b/tools/bpf/bpftool/btf_dumper.c
index 4e896d8a2416e..ff12628593aec 100644
--- a/tools/bpf/bpftool/btf_dumper.c
+++ b/tools/bpf/bpftool/btf_dumper.c
@@ -38,7 +38,7 @@ static int dump_prog_id_as_func_ptr(const struct btf_dumper *d,
 	__u32 info_len = sizeof(info);
 	const char *prog_name = NULL;
 	struct btf *prog_btf = NULL;
-	struct bpf_func_info finfo;
+	struct bpf_func_info finfo = {};
 	__u32 finfo_rec_size;
 	char prog_str[1024];
 	int err;
diff --git a/tools/bpf/bpftool/prog.c b/tools/bpf/bpftool/prog.c
index 9722d841abc05..a89629a9932b5 100644
--- a/tools/bpf/bpftool/prog.c
+++ b/tools/bpf/bpftool/prog.c
@@ -2262,7 +2262,7 @@ static void profile_print_readings(void)
 
 static char *profile_target_name(int tgt_fd)
 {
-	struct bpf_func_info func_info;
+	struct bpf_func_info func_info = {};
 	struct bpf_prog_info info = {};
 	__u32 info_len = sizeof(info);
 	const struct btf_type *t;
-- 
2.51.0