Re: [PATCH bpf-next 2/4] selftests/bpf: utility function to get program disassembly after jit

[Eduard Zingerman <eddyz87@gmail.com>]

On Tue, 2024-08-13 at 09:05 -0700, Yonghong Song wrote:

[...]

> > +	/* GCC can't figure max bound for i and thus reports possible truncation */
> > +#pragma GCC diagnostic push
> > +#pragma GCC diagnostic ignored "-Wformat-truncation"
> > +	for (i = 0; i < labels.cnt; ++i)
> > +		snprintf(labels.names[i], sizeof(labels.names[i]), "L%d", i);
> > +#pragma GCC diagnostic pop
> 
> "-Wformat-truncation" is only available for llvm >= 18. One of my build with llvm15
> has the following warning/error:
> 
> jit_disasm_helpers.c:113:32: error: unknown warning group '-Wformat-truncation', ignored [-Werror,-Wunknown-warning-option]
> #pragma GCC diagnostic ignored "-Wformat-truncation"
> 
> Maybe you want to guard with proper clang version?
> Not sure on gcc side when "-Wformat-truncation" is supported.

Thank you for catching this, I think I'll fix it as below in the v2.
Will wait for additional comments before submitting v2.

---

--- a/tools/testing/selftests/bpf/jit_disasm_helpers.c
+++ b/tools/testing/selftests/bpf/jit_disasm_helpers.c
@@ -108,12 +108,9 @@ static int disasm_one_func(FILE *text_out, uint8_t *image, __u32 len)
                pc += cnt;
        }
        qsort(labels.pcs, labels.cnt, sizeof(*labels.pcs), cmp_u32);
-       /* GCC can't figure max bound for i and thus reports possible truncation */
-#pragma GCC diagnostic push
-#pragma GCC diagnostic ignored "-Wformat-truncation"
        for (i = 0; i < labels.cnt; ++i)
-               snprintf(labels.names[i], sizeof(labels.names[i]), "L%d", i);
-#pragma GCC diagnostic pop
+               /* use (i % 100) to avoid format truncation warning */
+               snprintf(labels.names[i], sizeof(labels.names[i]), "L%d", i % 100);
 
        /* now print with labels */
        labels.print_phase = true;