On Wed, Feb 24, 2016 at 10:19 AM, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote: > Baremetal kernels clear .bss early in the boot but Xen PV guests don't > execute that code. They have been able to run without problems because > Xen domain builder happens to give out zeroed pages. However, since this > is not really guaranteed, .bss should be explicitly cleared. > > (Since we introduce macros for specifying 32- and 64-bit registers we > can get rid of ifdefs in startup_xen()) > > Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > --- > arch/x86/xen/xen-head.S | 29 ++++++++++++++++++++++------- > 1 file changed, 22 insertions(+), 7 deletions(-) > > diff --git a/arch/x86/xen/xen-head.S b/arch/x86/xen/xen-head.S > index b65f59a..2af87d1 100644 > --- a/arch/x86/xen/xen-head.S > +++ b/arch/x86/xen/xen-head.S > @@ -35,16 +35,31 @@ > #define PVH_FEATURES (0) > #endif > > - __INIT > -ENTRY(startup_xen) > - cld > #ifdef CONFIG_X86_32 > - mov %esi,xen_start_info > - mov $init_thread_union+THREAD_SIZE,%esp > +#define REG(register) %e##register > +#define WSIZE_SHIFT 2 > +#define STOS stosl > #else > - mov %rsi,xen_start_info > - mov $init_thread_union+THREAD_SIZE,%rsp > +#define REG(register) %r##register > +#define WSIZE_SHIFT 3 > +#define STOS stosq > #endif > + > + __INIT > +ENTRY(startup_xen) > + cld > + > + /* Clear .bss */ > + xor REG(ax),REG(ax) > + mov $__bss_start,REG(di) > + mov $__bss_stop,REG(cx) > + sub REG(di),REG(cx) > + shr $WSIZE_SHIFT,REG(cx) > + rep STOS > + > + mov REG(si),xen_start_info > + mov $init_thread_union+THREAD_SIZE,REG(sp) > + > jmp xen_start_kernel > > __FINIT Use the macros in <asm/asm.h> instead of defining your own. Also, xorl %eax,%eax is good for 64-bit too, since the upper bits are cleared. -- Brian Gerst -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html