Re: [PATCH] modpost: Warn about unused module namespace imports

[Andy Shevchenko <andriy.shevchenko@intel.com>]

On Thu, Jan 23, 2025 at 12:09:50PM +0100, Uwe Kleine-König wrote:
> Symbols can be exported in namespaces and to make use of such symbols,
> the namespace has to be explicitly imported. Importing a namespace
> without actually using one of its symbols is likely a mistake.
> 
> There are a few offenders for an x86_64 allmodconfig build, so the
> warning is (for now) only enabled for W=1 builds.
> 
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@baylibre.com>
> ---
> Hello,
> 
> one of the offenders is drivers/pwm/pwm-raspberrypi-poe.c (
> 
> 	WARNING: modpost: module pwm-raspberrypi-poe imports namespace PWM, but doesn't use it.
> 
> ). The issue there is that on x86_64 CONFIG_RASPBERRYPI_FIRMWARE is
> always disabled and so devm_rpi_firmware_get() returns always NULL which
> makes raspberrypi_pwm_probe return an error before the pwm functions are
> used. So the compiler optimizes out all references to pwm functions and
> the warning triggers. I didn't look into the other problems to check if
> these are similar half-false positives.
> 
> Still I think this is a useful check?

This will require to add a number of ugly ifdeffery to the kernel code like

MODULE_FOO();
#if ...
MODULE_IMPORT_NS();
#endif

I am definitely not okay with that.

Maybe you should introduce the MODULE_IMPORT_NS_IF_REACHABLE() or so to hide
this or whatever equivalent there?

-- 
With Best Regards,
Andy Shevchenko