linux-kernel - arch/x86/platform/efi/efi_64.c:212:15: sparse: memcpy with byte count of 0

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Date:   Wed, 10 May 2017 02:07:57 +0800
From:   kbuild test robot <fengguang.wu@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     kbuild-all@...org, linux-kernel@...r.kernel.org,
        Ingo Molnar <mingo@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>
Subject: arch/x86/platform/efi/efi_64.c:212:15: sparse: memcpy with byte
 count of 0

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
head:   2868b2513aa732a99ea4a0a6bf10dc93c1f3dac2
commit: e981316f560482c001dede7f5b29259bde0b8afb x86/efi: Add 5-level paging support
date:   6 weeks ago
reproduce:
        # apt-get install sparse
        git checkout e981316f560482c001dede7f5b29259bde0b8afb
        make ARCH=x86_64 allmodconfig
        make C=1 CF=-D__CHECK_ENDIAN__


sparse warnings: (new ones prefixed by >>)

>> arch/x86/platform/efi/efi_64.c:212:15: sparse: memcpy with byte count of 0

vim +212 arch/x86/platform/efi/efi_64.c

   196		num_entries = pgd_index(EFI_VA_END) - pgd_index(PAGE_OFFSET);
   197		memcpy(pgd_efi, pgd_k, sizeof(pgd_t) * num_entries);
   198	
   199		/*
   200		 * As with PGDs, we share all P4D entries apart from the one entry
   201		 * that covers the EFI runtime mapping space.
   202		 */
   203		BUILD_BUG_ON(p4d_index(EFI_VA_END) != p4d_index(MODULES_END));
   204		BUILD_BUG_ON((EFI_VA_START & P4D_MASK) != (EFI_VA_END & P4D_MASK));
   205	
   206		pgd_efi = efi_pgd + pgd_index(EFI_VA_END);
   207		pgd_k = pgd_offset_k(EFI_VA_END);
   208		p4d_efi = p4d_offset(pgd_efi, 0);
   209		p4d_k = p4d_offset(pgd_k, 0);
   210	
   211		num_entries = p4d_index(EFI_VA_END);
 > 212		memcpy(p4d_efi, p4d_k, sizeof(p4d_t) * num_entries);
   213	
   214		/*
   215		 * We share all the PUD entries apart from those that map the
   216		 * EFI regions. Copy around them.
   217		 */
   218		BUILD_BUG_ON((EFI_VA_START & ~PUD_MASK) != 0);
   219		BUILD_BUG_ON((EFI_VA_END & ~PUD_MASK) != 0);
   220	

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