Re: [linux-next:master 10679/10701] arch/x86/mm/pgtable.c:427:2: warning: variable length array 'u_pmds' is used

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 21 May 2020 03:56:53 +0800 kbuild test robot <lkp@intel.com> wrote:

> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git master
> head:   fb57b1fabcb28f358901b2df90abd2b48abc1ca8
> commit: 0e19fc1c40bd7516d5a30a459db4f49d48910847 [10679/10701] mm: consolidate pgd_index() and pgd_offset{_k}() definitions
> config: i386-randconfig-a005-20200520 (attached as .config)
> compiler: gcc-4.9 (Ubuntu 4.9.3-13ubuntu2) 4.9.3
> reproduce:
>         git checkout 0e19fc1c40bd7516d5a30a459db4f49d48910847
>         # save the attached .config to linux build tree
>         make ARCH=i386 
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kbuild test robot <lkp@intel.com>
> 
> All warnings (new ones prefixed by >>, old ones prefixed by <<):
> 
> arch/x86/mm/pgtable.c: In function 'pgd_alloc':
> >> arch/x86/mm/pgtable.c:427:2: warning: variable length array 'u_pmds' is used [-Wvla]
> pmd_t *u_pmds[MAX_PREALLOCATED_USER_PMDS];
> ^
> >> arch/x86/mm/pgtable.c:428:2: warning: variable length array 'pmds' is used [-Wvla]
> pmd_t *pmds[MAX_PREALLOCATED_PMDS];
> ^

Thanks.  This works for me - perhaps Mike can come up with something smarter.

--- a/include/linux/pgtable.h~mm-consolidate-pgd_index-and-pgd_offset_k-definitions-fix
+++ a/include/linux/pgtable.h
@@ -62,11 +62,8 @@ static inline unsigned long pud_index(un
 #endif
 
 #ifndef pgd_index
-static inline unsigned long pgd_index(unsigned long address)
-{
-	return ((address >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1));
-}
-#define pgd_index pgd_index
+/* Must be a compile-time constant, so implement it as a macro */
+#define pgd_index(a)  (((a) >> PGDIR_SHIFT) & (PTRS_PER_PGD - 1))
 #endif
 
 #ifndef pte_offset_kernel
_