linux-kernel - [ammarfaizi2-block:tglx/devel/depthtracking 2/45] arch/x86/kernel/cpu/common.c:760:37: error: implicit declaration of function 'cpu_kernelmode_gs

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Date:   Thu, 21 Jul 2022 18:00:43 +0800
From:   kernel test robot <lkp@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     kbuild-all@...ts.01.org, Ammar Faizi <ammarfaizi2@...weeb.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        linux-kernel@...r.kernel.org
Subject: [ammarfaizi2-block:tglx/devel/depthtracking 2/45]
 arch/x86/kernel/cpu/common.c:760:37: error: implicit declaration of function
 'cpu_kernelmode_gs_base'

tree:   https://github.com/ammarfaizi2/linux-block tglx/devel/depthtracking
head:   714d29e3e7e3faac27142424ae2533163ddd3a46
commit: 3adc8d7057cc2f5e8dbbaa4b7d8b68f94dadb6ad [2/45] x86/cpu: Remove segment load from switch_to_new_gdt()
config: i386-defconfig (https://download.01.org/0day-ci/archive/20220721/202207211722.nx5vSFbQ-lkp@intel.com/config)
compiler: gcc-11 (Debian 11.3.0-3) 11.3.0
reproduce (this is a W=1 build):
        # https://github.com/ammarfaizi2/linux-block/commit/3adc8d7057cc2f5e8dbbaa4b7d8b68f94dadb6ad
        git remote add ammarfaizi2-block https://github.com/ammarfaizi2/linux-block
        git fetch --no-tags ammarfaizi2-block tglx/devel/depthtracking
        git checkout 3adc8d7057cc2f5e8dbbaa4b7d8b68f94dadb6ad
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        make W=1 O=build_dir ARCH=i386 SHELL=/bin/bash

If you fix the issue, kindly add following tag where applicable
Reported-by: kernel test robot <lkp@...el.com>

All errors (new ones prefixed by >>):

   arch/x86/kernel/cpu/common.c: In function 'switch_to_new_gdt':
>> arch/x86/kernel/cpu/common.c:760:37: error: implicit declaration of function 'cpu_kernelmode_gs_base' [-Werror=implicit-function-declaration]
     760 |                 wrmsrl(MSR_GS_BASE, cpu_kernelmode_gs_base(cpu));
         |                                     ^~~~~~~~~~~~~~~~~~~~~~
   cc1: some warnings being treated as errors


vim +/cpu_kernelmode_gs_base +760 arch/x86/kernel/cpu/common.c

   730	
   731	/**
   732	 * switch_to_new_gdt - Switch form early GDT to the direct one
   733	 * @cpu:	The CPU number for which this is invoked
   734	 *
   735	 * Invoked during early boot to switch from early GDT and early per CPU
   736	 * (%fs on 32bit, GS_BASE on 64bit) to the direct GDT and the runtime per
   737	 * CPU area.
   738	 */
   739	void switch_to_new_gdt(int cpu)
   740	{
   741		load_direct_gdt(cpu);
   742	
   743		/*
   744		 * No need to load the %gs (%fs for 32bit) segment. It is already
   745		 * correct, %gs is 0 on 64bit and %fs is __KERNEL_PERCPU on 32 bit.
   746		 *
   747		 * Writing %gs on 64bit would zero GSBASE which would make any per
   748		 * CPU operation up to the point of the wrmsrl() fault.
   749		 *
   750		 * 64bit requires to point GSBASE to the new offset. Until the
   751		 * wrmsrl() happens the early mapping is still valid. That means
   752		 * the GSBASE update will lose any prior per CPU data which was
   753		 * not copied over in setup_per_cpu_areas().
   754		 *
   755		 * For secondary CPUs this is not a problem because they start
   756		 * already with the direct GDT and the real GSBASE. This invocation
   757		 * is pointless and will be removed in a subsequent step.
   758		 */
   759		if (IS_ENABLED(CONFIG_X86_64))
 > 760			wrmsrl(MSR_GS_BASE, cpu_kernelmode_gs_base(cpu));
   761	}
   762	

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