Thread (53 messages) 53 messages, 4 authors, 2020-05-05

Re: [PATCH v7 04/28] powerpc/xmon: Use bitwise calculations in_breakpoint_table()

From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2020-05-05 07:10:14

Jordan Niethe [off-list ref] writes:
quoted hunk ↗ jump to hunk
A modulo operation is used for calculating the current offset from a
breakpoint within the breakpoint table. As instruction lengths are
always a power of 2, this can be replaced with a bitwise 'and'. The
current check for word alignment can be replaced with checking that the
lower 2 bits are not set.

Suggested-by: Christophe Leroy <redacted>
Signed-off-by: Jordan Niethe <redacted>
---
v6: New to series
---
 arch/powerpc/xmon/xmon.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/powerpc/xmon/xmon.c b/arch/powerpc/xmon/xmon.c
index bbfea22f4a96..e122f0c8a044 100644
--- a/arch/powerpc/xmon/xmon.c
+++ b/arch/powerpc/xmon/xmon.c
@@ -857,8 +857,8 @@ static struct bpt *in_breakpoint_table(unsigned long nip, unsigned long *offp)
 	off = nip - (unsigned long) bpt_table;
 	if (off >= sizeof(bpt_table))
 		return NULL;
-	*offp = off % BPT_SIZE;
-	if (*offp != 0 && *offp != 4)
+	*offp = off & (BPT_SIZE - 1);
+	if (off & 3)
 		return NULL;
It would be even better if you didn't hard code the 3 wouldn't it?

eg:

+	*offp = off & (BPT_SIZE - 1);
+	if (off & (BPT_SIZE - 1))
 		return NULL;

cheers
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