On 12 Sep 2022, at 9:09 pm, Nicholas Piggin [off-list ref] wrote:

On Wed Aug 24, 2022 at 12:05 PM AEST, Rohan McLure wrote:

quoted

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.

Can I bikeshed this a bit more and ask if you would change the order?

Saving and restoring macros are incidental, and are neither the change
nor the reson for it. I think the changelog reads better if you state
the change (or the problem) up front.

Provid register zeroing macros ... follow the same convention as
existing register stack save/restore macros ... will be used in later
change to zero registers.

Thanks for the suggestion, that should read better.

Or not, if you disagree.

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>

quoted

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

Signed-off-by: Rohan McLure <redacted>
---
V1 -> V2: Change 'ZERO' usage in naming to 'NULLIFY', a more obvious verb
V2 -> V3: Change 'NULLIFY' usage in naming to 'ZEROIZE', which has
precedent in kernel and explicitly specifies that we are zeroing.
V3 -> V4: Update commit message to use zeroize.
---
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..b95689ada59c 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 ZEROIZE_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	ZEROIZE_GPRS(start, end)	ZEROIZE_REGS start, end
+#ifdef __powerpc64__
+#define	ZEROIZE_NVGPRS()		ZEROIZE_GPRS(14, 31)
+#else
+#define	ZEROIZE_NVGPRS()		ZEROIZE_GPRS(13, 31)
+#endif
+#define	ZEROIZE_GPR(n)			ZEROIZE_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