[bpf-next] bpf: eliminate remaining "make W=1" warnings in kernel/bpf/btf.o

Commit Message

Alan Maguire July 12, 2024, 9:28 a.m. UTC

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/[e-mail]/

Fixes: b3470da314fd ("bpf: annotate BTF show functions with __printf")
Suggested-by: Mirsad Todorovac <[e-mail]>
Reported-by: Mirsad Todorovac <[e-mail]>
Signed-off-by: Alan Maguire <[e-mail]>
---
 kernel/bpf/btf.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Comments

[e-mail] July 12, 2024, 3:10 p.m. UTC | #1

Hello:

This patch was applied to bpf/bpf-next.git (master)
by Daniel Borkmann <[e-mail]>:

On Fri, 12 Jul 2024 10:28:59 +0100 you wrote:
> 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;
>       |                               ^
> 
> [...]

Here is the summary with links:
  - [bpf-next] bpf: eliminate remaining "make W=1" warnings in kernel/bpf/btf.o
    https://git.kernel.org/bpf/bpf-next/c/2454075f8e29

You are awesome, thank you!

Patch

diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
index d5019c4454d6..520f49f422fe 100644
--- 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 {