[Xen-devel,v3,08/28] xen/arm32: head: Add a macro to move an immediate constant into a 32-bit register

Message ID 20190812173019.11956-9-julien.grall@arm.com
State New
Headers show
Series
  • xen/arm: Rework head.S to make it more compliant with the Arm Arm
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Commit Message

Julien Grall Aug. 12, 2019, 5:29 p.m.
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.grall@arm.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

---
    Changes in v3:
        - Add Stefano's acked-by

    Changes in v2:
        - Patch added
---
 xen/arch/arm/arm32/head.S | 9 +++++++++
 1 file changed, 9 insertions(+)

Patch

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  -