[Xen-devel] [PATCH] xen: arm: let the compiler choose the dummy register for TLB flush asm

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

While staring at some disassembly I noticed that the compiler was jumping
through hoops to preserve the function argument (in r0) simply so it could use
r0 as the dummy argument to the tlb flush cp register writes.

Remove the enforced use of r0 and use an output constraint for the dummy
register so there is no need to initialise the dummy.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 xen/include/asm-arm/arm32/page.h |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/xen/include/asm-arm/arm32/page.h b/xen/include/asm-arm/arm32/page.h
index d295316..86940ba 100644
--- a/xen/include/asm-arm/arm32/page.h
+++ b/xen/include/asm-arm/arm32/page.h
@@ -35,7 +35,7 @@ static inline void write_pte(lpae_t *p, lpae_t pte)
  */
 static inline void flush_xen_text_tlb(void)
 {
-    register unsigned long r0 asm ("r0");
+    unsigned long dummy;
     asm volatile (
         "isb;"                        /* Ensure synchronization with previous 
changes to text */
         STORE_CP32(0, TLBIALLH)       /* Flush hypervisor TLB */
@@ -43,7 +43,7 @@ static inline void flush_xen_text_tlb(void)
         STORE_CP32(0, BPIALL)         /* Flush branch predictor */
         "dsb;"                        /* Ensure completion of TLB+BP flush */
         "isb;"
-        : : "r" (r0) /*dummy*/ : "memory");
+        : "=r" (dummy) : : "memory");
 }
 
 /*
@@ -52,12 +52,12 @@ static inline void flush_xen_text_tlb(void)
  */
 static inline void flush_xen_data_tlb(void)
 {
-    register unsigned long r0 asm ("r0");
+    unsigned long dummy;
     asm volatile("dsb;" /* Ensure preceding are visible */
                  STORE_CP32(0, TLBIALLH)
                  "dsb;" /* Ensure completion of the TLB flush */
                  "isb;"
-                 : : "r" (r0) /* dummy */: "memory");
+                 : "=r" (dummy) : : "memory");
 }
 
 /*
-- 
1.7.2.5


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