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: <20250630192726.GBaGLlHl84xIopx4Pt@fat_crate.local>
Date: Mon, 30 Jun 2025 21:27:26 +0200
From: Borislav Petkov <bp@...en8.de>
To: kernel test robot <lkp@...el.com>
Cc: 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 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.

/facepalm 1

And the 0day bot - because it doesn't have anything better to do - is doing
W=1 builds. I did complain about that waste of resources in the past but
nothing happened.

/facepalm 2

> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250701/202507010218.3O5Ge0Xt-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@...el.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202507010218.3O5Ge0Xt-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
> >> arch/x86/coco/sev/core.c:2170:30: warning: variable 'dummy' set but not used [-Wunused-but-set-variable]
>     2170 |         unsigned long tsc_freq_mhz, dummy;
>          |                                     ^
>    1 warning generated.
> 
> 
> vim +/dummy +2170 arch/x86/coco/sev/core.c
> 
>   2167	
>   2168	void __init snp_secure_tsc_init(void)
>   2169	{
> > 2170		unsigned long tsc_freq_mhz, dummy;

And it is actually my damn fault because even if that dummy crap variable was
bugging me, I thought we want to "harmonize".

/facepalm 3

Which is a total nonsense because that code doesn't build in 32-bit.

So this should've stayed like this:

diff --git a/arch/x86/coco/sev/core.c b/arch/x86/coco/sev/core.c
index 47d10d9a28e9..36c167333d04 100644
--- a/arch/x86/coco/sev/core.c
+++ b/arch/x86/coco/sev/core.c
@@ -2167,8 +2167,8 @@ static unsigned long securetsc_get_tsc_khz(void)
 
 void __init snp_secure_tsc_init(void)
 {
-	unsigned long tsc_freq_mhz, dummy;
 	struct snp_secrets_page *secrets;
+	unsigned long tsc_freq_mhz;
 	void *mem;
 
 	if (!cc_platform_has(CC_ATTR_GUEST_SNP_SECURE_TSC))
@@ -2183,7 +2183,7 @@ void __init snp_secure_tsc_init(void)
 	secrets = (__force struct snp_secrets_page *)mem;
 
 	setup_force_cpu_cap(X86_FEATURE_TSC_KNOWN_FREQ);
-	rdmsr(MSR_AMD64_GUEST_TSC_FREQ, tsc_freq_mhz, dummy);
+	rdmsrq(MSR_AMD64_GUEST_TSC_FREQ, tsc_freq_mhz);
 	/* Extract the GUEST TSC MHZ from BIT[17:0], rest is reserved space */
 	tsc_freq_mhz = tsc_freq_mhz & GENMASK_ULL(17, 0);
 	snp_tsc_freq_khz = SNP_SCALE_TSC_FREQ(tsc_freq_mhz * 1000, secrets->tsc_factor);

What a f*cking mess. I don't have enough room on my face anymore from
facepalms.

Oh boy.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette