[PATCH v2 09/14] powerpc: Add NULLIFY_GPRS macros for register clears

[Rohan McLure <rmclure@linux.ibm.com>]

Macros for restoring and saving registers to and from the stack exist.
Provide macros with the same interface for clearing a range of gprs by
setting each register's value in that range to zero.

The resulting macros are called NULLIFY_GPRS and NULLIFY_NVGPRS, keeping
with the naming of the accompanying restore and save macros, and usage
of nullify to describe this operation elsewhere in the kernel.

Signed-off-by: Rohan McLure <rmclure@linux.ibm.com>
---
V1 -> V2: Change 'ZERO' usage in naming to 'NULLIFY', a more obvious verb
---
 arch/powerpc/include/asm/ppc_asm.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/arch/powerpc/include/asm/ppc_asm.h b/arch/powerpc/include/asm/ppc_asm.h
index 83c02f5a7f2a..d6c46082bf7f 100644
--- a/arch/powerpc/include/asm/ppc_asm.h
+++ b/arch/powerpc/include/asm/ppc_asm.h
@@ -33,6 +33,20 @@
 	.endr
 .endm
 
+/*
+ * This expands to a sequence of register clears for regs start to end
+ * inclusive, of the form:
+ *
+ *   li rN, 0
+ */
+.macro NULLIFY_REGS start, end
+	.Lreg=\start
+	.rept (\end - \start + 1)
+	li	.Lreg, 0
+	.Lreg=.Lreg+1
+	.endr
+.endm
+
 /*
  * Macros for storing registers into and loading registers from
  * exception frames.
@@ -49,6 +63,14 @@
 #define REST_NVGPRS(base)		REST_GPRS(13, 31, base)
 #endif
 
+#define	NULLIFY_GPRS(start, end)	NULLIFY_REGS start, end
+#ifdef __powerpc64__
+#define	NULLIFY_NVGPRS()		NULLIFY_GPRS(14, 31)
+#else
+#define	NULLIFY_NVGPRS()		NULLIFY_GPRS(13, 31)
+#endif
+#define	NULLIFY_GPR(n)			NULLIFY_GPRS(n, n)
+
 #define SAVE_GPR(n, base)		SAVE_GPRS(n, n, base)
 #define REST_GPR(n, base)		REST_GPRS(n, n, base)
 
-- 
2.34.1