Re: [PATCH] tracing: make ftrace_likely_update() declaration visible

[Linus Torvalds]

On Wed, May 17, 2023 at 5:47 AM Arnd Bergmann <arnd@xxxxxxxxxx> wrote:
>
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> This function is only used when CONFIG_TRACE_BRANCH_PROFILING is
> set, and the declaration is hidden behind this Kconfig symbol,
> which causes a warning if disabled:

That explanation is not very clear.

The problem is that the tracing code itself is built with
DISABLE_BRANCH_PROFILING, in order to not recurse. And that hides the
declaration when the definition is compiled, leading to the problem.

CONFIG_TRACE_BRANCH_PROFILING isn't the problem in itself - *that*
part of the test is consistent (not used, not declared, and not
compiled if it is off).

The problem is that DISABLE_BRANCH_PROFILING case, where it is used
elsewhere, but not declared when it is itself compiled.

I applied the patch, but I tried to reword the explanation to be more
clear. I may have failed.

          Linus