linux-kernel - [PATCH] x86/boot/arch/variable: I don't think (void *) Pointers need to be cast

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Message-Id: <20220725042358.3377-1-kunyu@nfschina.com>
Date:   Mon, 25 Jul 2022 12:23:58 +0800
From:   Li kunyu <kunyu@...china.com>
To:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Li kunyu <kunyu@...china.com>
Subject: [PATCH] x86/boot/arch/variable: I don't think (void *) Pointers need to be cast

I first observe (void *) type coercion and non coercion through assembly
language. It seems that there is no difference.
Then I output the assigned information through the print function and
found that the pointer that is not coerced is directly assigned when
executing the print function (opcode a1), while the coerced pointer
needs to execute the assembly instruction xlat (opcode d7), which seems
to be more efficient without coerced conversion.
At present, I just started to try to analyze this part of knowledge
(machine code), please forgive me if the analysis is wrong.

Signed-off-by: Li kunyu <kunyu@...china.com>
---
 arch/x86/boot/bitops.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/boot/bitops.h b/arch/x86/boot/bitops.h
index 02e1dea11d94..8518ae214c9b 100644
--- a/arch/x86/boot/bitops.h
+++ b/arch/x86/boot/bitops.h
@@ -19,13 +19,13 @@

 static inline bool constant_test_bit(int nr, const void *addr)
 {
-	const u32 *p = (const u32 *)addr;
+	const u32 *p = addr;
 	return ((1UL << (nr & 31)) & (p[nr >> 5])) != 0;
 }
 static inline bool variable_test_bit(int nr, const void *addr)
 {
 	bool v;
-	const u32 *p = (const u32 *)addr;
+	const u32 *p = addr;

 	asm("btl %2,%1" CC_SET(c) : CC_OUT(c) (v) : "m" (*p), "Ir" (nr));
 	return v;
-- 
2.18.2