linux-kernel - [PATCH] ARM: ptrace: Use bitfield helpers

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Date:   Mon, 22 Nov 2021 16:53:41 +0100
From:   Geert Uytterhoeven <geert+renesas@...der.be>
To:     Oleg Nesterov <oleg@...hat.com>,
        Russell King <linux@...linux.org.uk>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: [PATCH] ARM: ptrace: Use bitfield helpers

The isa_mode() macro extracts two fields, and recombines them into a
single value.  The shift value of the J-bit may look off-by-one to the
casual reader, as it is the net result of the extraction and
recombination steps.

Make this more obvious by using the FIELD_GET() helper, and shifting the
result into its final resting place.

Signed-off-by: Geert Uytterhoeven <geert+renesas@...der.be>
---
No changes in generated assembler code.

See "[PATCH 00/17] Non-const bitfield helper conversions"
(https://lore.kernel.org/r/cover.1637592133.git.geert+renesas@glider.be)
for background and more conversions.
---
 arch/arm/include/asm/ptrace.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
index 93051e2f402c8452..982514aa83c1f459 100644
--- a/arch/arm/include/asm/ptrace.h
+++ b/arch/arm/include/asm/ptrace.h
@@ -10,6 +10,7 @@
 #include <uapi/asm/ptrace.h>
 
 #ifndef __ASSEMBLY__
+#include <linux/bitfield.h>
 #include <linux/types.h>
 
 struct pt_regs {
@@ -35,8 +36,8 @@ struct svc_pt_regs {
 
 #ifndef CONFIG_CPU_V7M
 #define isa_mode(regs) \
-	((((regs)->ARM_cpsr & PSR_J_BIT) >> (__ffs(PSR_J_BIT) - 1)) | \
-	 (((regs)->ARM_cpsr & PSR_T_BIT) >> (__ffs(PSR_T_BIT))))
+	((FIELD_GET(PSR_J_BIT, (regs)->ARM_cpsr) << 1) | \
+	 FIELD_GET(PSR_T_BIT, (regs)->ARM_cpsr))
 #else
 #define isa_mode(regs) 1 /* Thumb */
 #endif
-- 
2.25.1