[Xen-devel] [PATCH v4 4/6] xen: arm32: don't force the compiler to allocate a dummy register

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

TLBIALLH, ICIALLU and BPIALL make no use of their register argument. Instead
of making the compiler allocate a dummy register just hardcode r0, there is no
need to represent this in the inline asm since the register is neither
clobbered nor used in any way.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
Acked-by: Julien Grall <julien.grall@xxxxxxxxxx>
---
 xen/include/asm-arm/arm32/page.h      |   14 ++++++--------
 xen/include/asm-arm/arm32/processor.h |    4 ++++
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/xen/include/asm-arm/arm32/page.h b/xen/include/asm-arm/arm32/page.h
index ead6b97..3f2bdc9 100644
--- a/xen/include/asm-arm/arm32/page.h
+++ b/xen/include/asm-arm/arm32/page.h
@@ -37,15 +37,14 @@ static inline void write_pte(lpae_t *p, lpae_t pte)
  */
 static inline void flush_xen_text_tlb_local(void)
 {
-    register unsigned long r0 asm ("r0");
     asm volatile (
         "isb;"                        /* Ensure synchronization with previous 
changes to text */
-        STORE_CP32(0, TLBIALLH)       /* Flush hypervisor TLB */
-        STORE_CP32(0, ICIALLU)        /* Flush I-cache */
-        STORE_CP32(0, BPIALL)         /* Flush branch predictor */
+        CMD_CP32(TLBIALLH)            /* Flush hypervisor TLB */
+        CMD_CP32(ICIALLU)             /* Flush I-cache */
+        CMD_CP32(BPIALL)              /* Flush branch predictor */
         "dsb;"                        /* Ensure completion of TLB+BP flush */
         "isb;"
-        : : "r" (r0) /*dummy*/ : "memory");
+        : : : "memory");
 }
 
 /*
@@ -55,12 +54,11 @@ static inline void flush_xen_text_tlb_local(void)
  */
 static inline void flush_xen_data_tlb_local(void)
 {
-    register unsigned long r0 asm ("r0");
     asm volatile("dsb;" /* Ensure preceding are visible */
-                 STORE_CP32(0, TLBIALLH)
+                 CMD_CP32(TLBIALLH)
                  "dsb;" /* Ensure completion of the TLB flush */
                  "isb;"
-                 : : "r" (r0) /* dummy */: "memory");
+                 : : : "memory");
 }
 
 /* Flush TLB of local processor for address va. */
diff --git a/xen/include/asm-arm/arm32/processor.h 
b/xen/include/asm-arm/arm32/processor.h
index 8a35cee..f41644d 100644
--- a/xen/include/asm-arm/arm32/processor.h
+++ b/xen/include/asm-arm/arm32/processor.h
@@ -69,6 +69,10 @@ struct cpu_user_regs
 #define LOAD_CP64(r, name...)  "mrrc " __stringify(CP64(%r, %H##r, name)) ";"
 #define STORE_CP64(r, name...) "mcrr " __stringify(CP64(%r, %H##r, name)) ";"
 
+/* Issue a CP operation which takes no argument,
+ * uses r0 as a placeholder register. */
+#define CMD_CP32(name...)      "mcr " __stringify(CP32(r0, name)) ";"
+
 #ifndef __ASSEMBLY__
 
 /* C wrappers */
-- 
1.7.10.4


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