-Wfortify-source in kernel/printk/printk.c

[Nathan Chancellor]

Hi all,

After commit 6d485ff455e ("Improve static checks for sprintf and
__builtin___sprintf_chk") in clang [1], the following warning appears
when CONFIG_PRINTK is disabled (e.g. allnoconfig):

../kernel/printk/printk.c:2416:10: warning: 'sprintf' will always
overflow; destination buffer has size 0, but format string expands
to at least 33 [-Wfortify-source]
                        len = sprintf(text,
                              ^
1 warning generated.

Specifically referring to
https://elixir.bootlin.com/linux/v5.5/source/kernel/printk/printk.c#L2416.

It isn't wrong, given that when CONFIG_PRINTK is disabled, text's length
is 0 (LOG_LINE_MAX and PREFIX_MAX are both zero). How should this
warning be dealt this? I am not familiar enough with the printk code to
say myself.

[1]: https://github.com/llvm/llvm-project/commit/6d485ff455ea2b37fef9e06e426dae6c1241b231

Cheers,
Nathan