Messages in this thread | | | Date | Fri, 16 Dec 2016 23:19:16 -0500 | From | Jérémy Lefaure <> | Subject | Re: [PATCH] x86/vm86: fix compilation warning on a unused variable |
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On Mon, 12 Dec 2016 17:52:50 +0300 "Kirill A. Shutemov" <kirill@shutemov.name> wrote:
> On Thu, Dec 08, 2016 at 01:25:37PM -0500, Jérémy Lefaure wrote: > > On Thu, 8 Dec 2016 13:50:11 +0300 > > "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote: > > > > > On Wed, Dec 07, 2016 at 11:38:33PM -0500, Jérémy Lefaure wrote: > > > > When CONFIG_TRANSPARENT_HUGEPAGE is disabled, split_huge_pmd is a no-op > > > > stub. In such case, vma is unused and a compiler raises a warning: > > > > > > > > arch/x86/kernel/vm86_32.c: In function ‘mark_screen_rdonly’: > > > > arch/x86/kernel/vm86_32.c:180:26: warning: unused variable ‘vma’ > > > > [-Wunused-variable] > > > > struct vm_area_struct *vma = find_vma(mm, 0xA0000); > > > > ^~~ > > > > Adding __maybe_unused in the vma declaration fixes this warning. > > > > > > Hm. pmd_trans_huge() is zero if CONFIG_TRANSPARENT_HUGEPAGE is not set. > > > Compiler should get rid of whole block of code under the 'if'. > > > > > > Could you share your kernel config which triggers the warning? > > > And what compiler do you use? > > > > > > > After a `make allnoconfig`, I enable "Legacy VM86 support" and nothing > > else. I tested with 2 compilers, gcc 4.9.2 (on debian jessie) and gcc > > 6.2.1 (on archlinux). > > > > Actually, the compiler does not raise warnings on complete build (`make > > mrproper`, configuration and `make`) but only on partial build (`make > > arch/x86/kernel/vm86_32.o` or `touch arch/x86/kernel/vm86_32.c && > > make`). So maybe it is a compiler issue ? > > Sorry, forget about this part, it's false. I may have tested too quickly and missed something.
> > The solution you propose in your other email (adding "(void)__vma;" in > > the no-op split_huge_pmd) seems to fix the warnings on partial build. > > This doesn't make any sense, but this works too: > I don't know why gcc raises a warning on that even if it is not used. Anyway, I'm sure that the warning is reproducible. Both of your solutions fix the issue.
> diff --git a/arch/x86/kernel/vm86_32.c b/arch/x86/kernel/vm86_32.c > index e339717af265..63ddc598f5a9 100644 > --- a/arch/x86/kernel/vm86_32.c > +++ b/arch/x86/kernel/vm86_32.c > @@ -160,6 +160,7 @@ void save_v86_state(struct kernel_vm86_regs *regs, int retval) > > static void mark_screen_rdonly(struct mm_struct *mm) > { > + struct vm_area_struct *vma; > pgd_t *pgd; > p4d_t *p4d; > pud_t *pud; > @@ -181,7 +182,7 @@ static void mark_screen_rdonly(struct mm_struct *mm) > pmd = pmd_offset(pud, 0xA0000); > > if (pmd_trans_huge(*pmd)) { > - struct vm_area_struct *vma = find_vma(mm, 0xA0000); > + vma = find_vma(mm, 0xA0000); > split_huge_pmd(vma, pmd, 0xA0000); > } > if (pmd_none_or_clear_bad(pmd))
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