linux-kernel - Re: [PATCH v1 1/1] platform/x86: ideapad-laptop: Make the scope

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Message-ID: <cf8c73dd91dbbb11b562a5e0d9ac6b4035c32d28.camel@irl.hu>
Date: Tue, 03 Sep 2024 17:00:51 +0200
From: Gergo Koteles <soyer@....hu>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
  Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
  Hans de Goede <hdegoede@...hat.com>,
  platform-driver-x86@...r.kernel.org, linux-kernel@...r.kernel.org
Cc: Ike Panhc <ike.pan@...onical.com>,
  Peter Zijlstra <peterz@...radead.org>,
  Josh Poimboeuf <jpoimboe@...nel.org>,
  Nathan Chancellor <nathan@...nel.org>,
  kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v1 1/1] platform/x86: ideapad-laptop: Make the
 scope_guard() clear of its scope

Hi Andy,

Thank you for addressing this.

On Thu, 2024-08-29 at 19:50 +0300, Andy Shevchenko wrote:
> First of all, it's a bit counterintuitive to have something like
> 
> 	int err;
> 	...
> 	scoped_guard(...)
> 		err = foo(...);
> 	if (err)
> 		return err;
> 
> Second, with a particular kernel configuration and compiler version in
> one of such cases the objtool is not happy:
> 
>   ideapad-laptop.o: warning: objtool: .text.fan_mode_show: unexpected end of section
> 
> I'm not an expert on all this, but the theory is that compiler and
> linker in this case can't understand that 'result' variable will be
> always initialized as long as no error has been returned. Assigning
> 'result' to a dummy value helps with this. Note, that fixing the
> scoped_guard() scope (as per above) does not make issue gone.
> 
> That said, assign dummy value and make the scope_guard() clear of its scope.
> For the sake of consistency do it in the entire file.
> 

Interestingly, if I open a scope manually and use the plain guard, the
warning disappears.

	...
	unsigned long result;
	int err;

	{
		guard(mutex)(&priv->vpc_mutex);
		err = read_ec_data(priv->adev->handle, VPCCMD_R_FAN,
&result);
		if (err)
			return err;
	}
	...

This looks a bit strange, but is probably easier for the compiler than
the for loop of scoped_guard.

But I don't know how well this style fits into the kernel.

Best regards,
Gergo Koteles