On Wed, Aug 23, 2017 at 03:07:04PM +0100, Ard Biesheuvel wrote:
> On 23 August 2017 at 15:05, Arnd Bergmann <a...@arndb.de> wrote:
> > gcc-8 correctly points out that reading four bytes from a pointer to a
> > 'char' variable is wrong
> >
> > arch/arm/kernel/vdso.c: In function 'vdso_init':
> > arch/arm/kernel/vdso.c:200:6: error: '__builtin_memcmp_eq' reading 4 bytes
> > from a region of size 1 [-Werror=stringop-overflow=]
> >
> > However, in this case the variable just stands for the beginning of the
> > vdso and is not actually a 'char', so the code is doing what it is meant
> > to do.
> >
> > Not sure what the best solution for this is, changing the hack to
> > declare the variable as 'int' instead makes the warning go away.
> >
> > Signed-off-by: Arnd Bergmann <a...@arndb.de>
> > ---
> > arch/arm/include/asm/vdso.h | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/arch/arm/include/asm/vdso.h b/arch/arm/include/asm/vdso.h
> > index d0295f1dd1a3..eff7d3a1d1ce 100644
> > --- a/arch/arm/include/asm/vdso.h
> > +++ b/arch/arm/include/asm/vdso.h
> > @@ -11,7 +11,7 @@ struct mm_struct;
> >
> > void arm_install_vdso(struct mm_struct *mm, unsigned long addr);
> >
> > -extern char vdso_start, vdso_end;
> > +extern int vdso_start, vdso_end;
> >
> > extern unsigned int vdso_total_pages;
>
> May I suggest
>
> extern char vdso_start[], vdso_end[];
FWIW, arm64 does this to solve this problem, since commit:
dbbb08f500d61463 ("arm64, vdso: Define vdso_{start,end} as array")
... and x86 has done likewise for a while.
Thanks,
Mark.
