Patchwork ARM: KVM: fix warning in mmu.c

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Submitter Marc Zyngier
Date Feb. 5, 2014, 7:58 p.m.
Message ID <1391630305-8056-1-git-send-email-marc.zyngier@arm.com>
Download mbox | patch
Permalink /patch/317269/
State New
Headers show

Comments

Marc Zyngier - Feb. 5, 2014, 7:58 p.m.
Compiling with THP enabled leads to the following warning:

arch/arm/kvm/mmu.c: In function ‘unmap_range’:
arch/arm/kvm/mmu.c:177:39: warning: ‘pte’ may be used uninitialized in this function [-Wmaybe-uninitialized]
   if (kvm_pmd_huge(*pmd) || page_empty(pte)) {
                                        ^
Code inspection reveals that these two cases are mutually exclusive,
so GCC is a bit overzealous here. But silence it anyway by setting
pte to NULL if kvm_pmd_huge(*pmd) is true.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
 arch/arm/kvm/mmu.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
Christoffer Dall - Feb. 7, 2014, 3:51 a.m.
On Wed, Feb 05, 2014 at 07:58:25PM +0000, Marc Zyngier wrote:
> Compiling with THP enabled leads to the following warning:
> 
> arch/arm/kvm/mmu.c: In function ‘unmap_range’:
> arch/arm/kvm/mmu.c:177:39: warning: ‘pte’ may be used uninitialized in this function [-Wmaybe-uninitialized]
>    if (kvm_pmd_huge(*pmd) || page_empty(pte)) {
>                                         ^
> Code inspection reveals that these two cases are mutually exclusive,
> so GCC is a bit overzealous here. But silence it anyway by setting
> pte to NULL if kvm_pmd_huge(*pmd) is true.
> 
> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
> ---
>  arch/arm/kvm/mmu.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index ea21b6a..3020221 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -169,12 +169,14 @@ static void unmap_range(struct kvm *kvm, pgd_t *pgdp,
>  			pte = pte_offset_kernel(pmd, addr);
>  			clear_pte_entry(kvm, pte, addr);
>  			next = addr + PAGE_SIZE;
> +		} else {
> +			pte = NULL;
>  		}

If it's just for the compiler, how about just setting pte = NULL when
pte is declared in the top of the function as to not interrupt the flow?

-Christoffer

Patch

diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
index ea21b6a..3020221 100644
--- a/arch/arm/kvm/mmu.c
+++ b/arch/arm/kvm/mmu.c
@@ -169,12 +169,14 @@  static void unmap_range(struct kvm *kvm, pgd_t *pgdp,
 			pte = pte_offset_kernel(pmd, addr);
 			clear_pte_entry(kvm, pte, addr);
 			next = addr + PAGE_SIZE;
+		} else {
+			pte = NULL;
 		}
 
 		/*
 		 * If the pmd entry is to be cleared, walk back up the ladder
 		 */
-		if (kvm_pmd_huge(*pmd) || page_empty(pte)) {
+		if (kvm_pmd_huge(*pmd) || (pte && page_empty(pte))) {
 			clear_pmd_entry(kvm, pmd, addr);
 			next = pmd_addr_end(addr, end);
 			if (page_empty(pmd) && !page_empty(pud)) {