tree:   https://git.kernel.org/pub/scm/linux/kernel/git/joro/linux.git sev-es-kexec
head:   3467dc3cdbe65c619cd9b5c8db47da63b0655300
commit: 2740e3cdcb62ce9ce27839885b033c3d1f647710 [7/12] x86/sev: Setup code to park APs in the AP Jump Table
config: x86_64-randconfig-a004-20210702 (attached as .config)
compiler: clang version 13.0.0 (https://github.com/llvm/llvm-project 9eb613b2de3163686b1a4bd1160f15ac56a4b083)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install x86_64 cross compiling tool for clang build
        # apt-get install binutils-x86-64-linux-gnu
        # https://git.kernel.org/pub/scm/linux/kernel/git/joro/linux.git/commit/?id=2740e3cdcb62ce9ce27839885b033c3d1f647710
        git remote add joro https://git.kernel.org/pub/scm/linux/kernel/git/joro/linux.git
        git fetch --no-tags joro sev-es-kexec
        git checkout 2740e3cdcb62ce9ce27839885b033c3d1f647710
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> arch/x86/kernel/sev.c:762:13: warning: no previous prototype for function 'sev_es_setup_ap_jump_table_data' [-Wmissing-prototypes]
   void __init sev_es_setup_ap_jump_table_data(void *base, u32 pa)
               ^
   arch/x86/kernel/sev.c:762:1: note: declare 'static' if the function is not intended to be used outside of this translation unit
   void __init sev_es_setup_ap_jump_table_data(void *base, u32 pa)
   ^
   static 
   1 warning generated.


vim +/sev_es_setup_ap_jump_table_data +762 arch/x86/kernel/sev.c

   755	
   756	/*
   757	 * This function make the necessary runtime changes to the AP Jump Table blob.
   758	 * For now this only sets up the GDT used while the code executes. The GDT needs
   759	 * to contain 16-bit code and data segments with a base that points to AP Jump
   760	 * Table page.
   761	 */
 > 762	void __init sev_es_setup_ap_jump_table_data(void *base, u32 pa)
   763	{
   764		struct sev_ap_jump_table_header *header;
   765		struct desc_ptr *gdt_descr;
   766		u64 *ap_jumptable_gdt;
   767	
   768		header = base;
   769	
   770		/*
   771		 * Setup 16-bit protected mode code and data segments for AP Jumptable.
   772		 * Set the segment limits to 0xffff to already be compatible with
   773		 * real-mode.
   774		 */
   775		ap_jumptable_gdt = (u64 *)(base + header->gdt_offset);
   776		ap_jumptable_gdt[SEV_APJT_CS16 / 8] = GDT_ENTRY(0x9b, pa, 0xffff);
   777		ap_jumptable_gdt[SEV_APJT_DS16 / 8] = GDT_ENTRY(0x93, pa, 0xffff);
   778	
   779		/* Write correct GDT base address into GDT descriptor */
   780		gdt_descr = (struct desc_ptr *)(base + header->gdt_offset);
   781		gdt_descr->address += pa;
   782	}
   783	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org