On Tue, Feb 3, 2026, at 18:24, Alexei Starovoitov wrote:
> On Tue, Feb 3, 2026 at 8:58 AM Arnd Bergmann <[email protected]> wrote:
>> On Tue, Feb 3, 2026, at 17:34, Alexei Starovoitov wrote:
>> > On Tue, Feb 3, 2026 at 8:27 AM Arnd Bergmann <[email protected]> wrote:
>> >>
>> >> From: Arnd Bergmann <[email protected]>
>> >>
>> >> Some internal functions in bpf produce a warning when
>> >> -Wsuggest-attribute=format
>> >> is passed to the compiler, e.g. in 'make W=1':
>> >>
>> >> kernel/trace/bpf_trace.c: In function '____bpf_trace_printk':
>> >> kernel/trace/bpf_trace.c:377:9: error: function '____bpf_trace_printk'
>> >> might be a candidate for 'gnu_printf' format attribute
>> >> [-Werror=suggest-attribute=format]
>> >> 377 | ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt,
>> >> data.bin_args);
>> >> | ^~~
>> >>
>> >> The attribute here is useless since there are no callers from C code,
>> >> but it helps to shut up the output anyway so we can eventually turn
>> >> the warning option on by default.
>> >>
>> >> Signed-off-by: Arnd Bergmann <[email protected]>
>> >
>> > This was discussed and it's incorrect.
>>
>> Do you have a reference to why it's incorrect? It seems harmless
>> and gives me a clean kernel build in combination with a handful
>> of other fixes after enabling the option by default, but I assume
>> I'm missing something,
>
> because it's not a printf format. There are no varags here.
> gnu_printf attribute takes two arguments:
> format (archetype, string-index, first-to-check)
> Also
> "GCC requires a function with the 'format' attribute to be variadic"
My impression was that at least vbin_printf() falls into the
same category as vprintf(), which is explictly mentioned in the
gcc documentation:
For functions where the arguments are not available to be checked
(such as 'vprintf'), specify the third parameter as zero.
I also see the comment about bstr_printf() mention that it
uses a vsnprintf() compatible format, which would indicate that
marking the format argument isn't wrong, though I agree it is
not actually useful if there are no callers that pass a string
literal.
>> > Commit 7bf819aa992f ("vsnprintf: Mark binary printing functions with
>> > __printf() attribute") should be reverted instead.
>>
>> Reverting that one would appear to introduce warnings elsewhere,
>> so that would not be a complete fix either.
>
> Somebody needs to root cause it and fix it properly.
> Adding more incorrect annotation is not a solution.
I've tried reverting it here now, will see what I can come up
with. We can probably use the same trick that I used "[PATCH]
[v2] tracing: move __printf() attribute on __ftrace_vbprintk()",
annotate only the definition but not the declaration so the
format string warning doesn't propagate to the callers.
Arnd
