On Mon, 22 Jul 2019, Julien Grall wrote: > The current boot code is using the pattern ldr rX, =... to move an > immediate constant into a 32-bit register. > > This pattern implies to load the immediate constant from a literal pool, > meaning a memory access will be performed. > > The memory access can be avoided by using movw/movt instructions. > > A new macro is introduced to move an immediate constant into a 32-bit > register without a memory load. Follow-up patches will make use of it. > > Signed-off-by: Julien Grall <julien.gr...@arm.com>
That's interesting! Acked-by: Stefano Stabellini <sstabell...@kernel.org> > --- > Changes in v2: > - Patch added > --- > xen/arch/arm/arm32/head.S | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S > index 18ded49a04..99f4af18d8 100644 > --- a/xen/arch/arm/arm32/head.S > +++ b/xen/arch/arm/arm32/head.S > @@ -37,6 +37,15 @@ > #endif > > /* > + * Move an immediate constant into a 32-bit register using movw/movt > + * instructions. > + */ > +.macro mov_w reg, word > + movw \reg, #:lower16:\word > + movt \reg, #:upper16:\word > +.endm > + > +/* > * Common register usage in this file: > * r0 - > * r1 - > -- > 2.11.0 > _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
