On Mon, Dec 15, 2025 at 9:36 AM Andrii Nakryiko <[email protected]> wrote: > > On Wed, Dec 10, 2025 at 5:12 AM Andy Shevchenko > <[email protected]> wrote: > > > > The printing functions in BPF code are using printf() type of format, > > and compiler is not happy about them as is: > > > > kernel/bpf/helpers.c:1069:9: error: function ‘____bpf_snprintf’ might be a > > candidate for ‘gnu_printf’ format attribute > > [-Werror=suggest-attribute=format] > > 1069 | err = bstr_printf(str, str_size, fmt, data.bin_args); > > | ^~~ > > > > kernel/bpf/stream.c:241:9: error: function ‘bpf_stream_vprintk_impl’ might > > be a candidate for ‘gnu_printf’ format attribute > > [-Werror=suggest-attribute=format] > > 241 | ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt__str, > > data.bin_args); > > | ^~~ > > > > 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); > > | ^~~ > > > > kernel/trace/bpf_trace.c:433:9: error: function ‘____bpf_trace_vprintk’ > > might be a candidate for ‘gnu_printf’ format attribute > > [-Werror=suggest-attribute=format] > > 433 | ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt, > > data.bin_args); > > | ^~~ > > > > kernel/trace/bpf_trace.c:475:9: error: function ‘____bpf_seq_printf’ might > > be a candidate for ‘gnu_printf’ format attribute > > [-Werror=suggest-attribute=format] > > 475 | seq_bprintf(m, fmt, data.bin_args); > > | ^~~~~~~~~~~ > > > > I just want to point out that the compiler suggestion is wrong here > and these functions do not follow printf semantics. Yes, they have > printf format string argument, but arguments themselves are passed > using a special convention that the compiler won't know how to verify > properly. So now, these are not candidates for gnu_printf, and it > would be nice to have some way to shut up GCC for individual function > instead of blanket -Wno-suggest-attribute for the entire file. > > Similarly, I see you marked bstr_printf() with __printf() earlier. > That also seems wrong, so you might want to fix that mistake as well, > while at it. > > Maybe the pragma push/pop approach would be a bit better and more > explicit in the code?
I suggested using makefile and file level disable to avoid polluting the code. Even when attr-print applies it doesn't help definitions. The attribute is only useful in declaration and in our case it's not going to be in vmlinux.h or in bpf_helpers.h So having it right or wrong in .c is misleading.
