linux-kernel - Re: [tip:x86/urgent 1/1] arch/x86/coco/sev/core.c:2170:30: warning: variable 'dummy' set but not used

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Message-ID: <20250701150644.GA3563357@ax162>
Date: Tue, 1 Jul 2025 08:06:44 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: Borislav Petkov <bp@...en8.de>
Cc: kernel test robot <lkp@...el.com>, Nikunj A Dadhania <nikunj@....com>,
	llvm@...ts.linux.dev, oe-kbuild-all@...ts.linux.dev,
	linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [tip:x86/urgent 1/1] arch/x86/coco/sev/core.c:2170:30: warning:
 variable 'dummy' set but not used

On Mon, Jun 30, 2025 at 09:27:26PM +0200, Borislav Petkov wrote:
> On Tue, Jul 01, 2025 at 02:43:31AM +0800, kernel test robot wrote:
> > tree:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86/urgent
> > head:   4a35d2b5254af89595fd90dae9ee0c8f990a148d
> > commit: 4a35d2b5254af89595fd90dae9ee0c8f990a148d [1/1] x86/sev: Use TSC_FACTOR for Secure TSC frequency calculation
> > config: x86_64-allyesconfig (https://download.01.org/0day-ci/archive/20250701/202507010218.3O5Ge0Xt-lkp@intel.com/config)
> > compiler: clang version 20.1.7 (https://github.com/llvm/llvm-project 6146a88f60492b520a36f8f8f3231e15f3cc6082)
> 
> Pff, doesn't fire with clang-19.
> 
> That damn compiler.
> 
> gcc used to complain about those but they fixed their interprocedural analysis
> or whatnot.
> 
> clang is simply complaining more.

Citation needed. This reproduces with Clang 15 (earliest supported on
x86 now), Clang 19, and GCC 15 for me. Were you missing W=1?

  $ x86_64-linux-gcc --version | head -1
  x86_64-linux-gcc (GCC) 15.1.0

  $ curl -LSso .config https://download.01.org/0day-ci/archive/20250701/202507010218.3O5Ge0Xt-lkp@intel.com/config

  $ make -skj"$(nproc)" ARCH=x86_64 CROSS_COMPILE=x86_64-linux- W=1 olddefconfig arch/x86/coco/sev/core.o
  arch/x86/coco/sev/core.c: In function 'snp_secure_tsc_init':
  arch/x86/coco/sev/core.c:2170:37: warning: variable 'dummy' set but not used [-Wunused-but-set-variable]
   2170 |         unsigned long tsc_freq_mhz, dummy;
        |                                     ^~~~~

Cheers,
Nathan