bpf: Eliminate remaining "make W=1" warnings in kernel/bpf/btf.o

As reported by Mirsad [1] we still see format warnings in kernel/bpf/btf.o
at W=1 warning level:

  CC      kernel/bpf/btf.o
./kernel/bpf/btf.c: In function ‘btf_type_seq_show_flags’:
./kernel/bpf/btf.c:7553:21: warning: assignment left-hand side might be a candidate for a format attribute [-Wsuggest-attribute=format]
 7553 |         sseq.showfn = btf_seq_show;
      |                     ^
./kernel/bpf/btf.c: In function ‘btf_type_snprintf_show’:
./kernel/bpf/btf.c:7604:31: warning: assignment left-hand side might be a candidate for a format attribute [-Wsuggest-attribute=format]
 7604 |         ssnprintf.show.showfn = btf_snprintf_show;
      |                               ^

Combined with CONFIG_WERROR=y these can halt the build.

The fix (annotating the structure field with __printf())
suggested by Mirsad resolves these. Apologies I missed this last time.
No other W=1 warnings were observed in kernel/bpf after this fix.

[1] https://lore.kernel.org/bpf/92c9d047-f058-400c-9c7d-81d4dc1ef71b@gmail.com/

Fixes: b3470da314fd ("bpf: annotate BTF show functions with __printf")
Reported-by: Mirsad Todorovac <mtodorovac69@gmail.com>
Suggested-by: Mirsad Todorovac <mtodorovac69@gmail.com>
Signed-off-by: Alan Maguire <alan.maguire@oracle.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240712092859.1390960-1-alan.maguire@oracle.com

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index d5019c4454d64fac59c301c65d88b64f27d43d46..520f49f422fee232f728029e185b258183ac7c51 100644 (file)
--- a/kernel/bpf/btf.c
+++ b/kernel/bpf/btf.c
@@ -415,7 +415,7 @@ const char *btf_type_str(const struct btf_type *t)
 struct btf_show {
        u64 flags;
        void *target;   /* target of show operation (seq file, buffer) */
-       void (*showfn)(struct btf_show *show, const char *fmt, va_list args);
+       __printf(2, 0) void (*showfn)(struct btf_show *show, const char *fmt, va_list args);
        const struct btf *btf;
        /* below are used during iteration */
        struct {