[Xen-devel] [PATCH v2 18/35] xen/arm64: head: Introduce a macro to get a PC-relative address of a symbol

[Julien Grall <julien.grall@xxxxxxx>]

Arm64 provides instructions to load a PC-relative address, but with some
limitations:
   - adr is enable to cope with +/-1MB
   - adrp is enale to cope with +/-4GB but relative to a 4KB page
     address

Because of that, the code requires to use 2 instructions to load any Xen
symbol. To make the code more obvious, introducing a new macro adr_l is
introduced.

The new macro is used to replace a couple of open-coded use in
efi_xen_start.

The macro is copied from Linux 5.2-rc4.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>

---
    Changes in v2:
        - Patch added
---
 xen/arch/arm/arm64/head.S | 18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index 9afd89d447..2287f3ce48 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -111,6 +111,18 @@
 
 #endif /* !CONFIG_EARLY_PRINTK */
 
+/*
+ * Pseudo-op for PC relative adr <reg>, <symbol> where <symbol> is
+ * within the range +/- 4GB of the PC.
+ *
+ * @dst: destination register (64 bit wide)
+ * @sym: name of the symbol
+ */
+.macro  adr_l, dst, sym
+        adrp \dst, \sym
+        add  \dst, \dst, :lo12:\sym
+.endm
+
 /* Load the physical address of a symbol into xb */
 .macro load_paddr xb, sym
         ldr \xb, =\sym
@@ -886,11 +898,9 @@ ENTRY(efi_xen_start)
          * Flush dcache covering current runtime addresses
          * of xen text/data. Then flush all of icache.
          */
-        adrp  x1, _start
-        add   x1, x1, #:lo12:_start
+        adr_l x1, _start
         mov   x0, x1
-        adrp  x2, _end
-        add   x2, x2, #:lo12:_end
+        adr_l x2, _end
         sub   x1, x2, x1
 
         bl    __flush_dcache_area
-- 
2.11.0


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