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From: Lukas Bulwahn <lukas.bulwahn@gmail.com>
To: Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
	kernel-janitors@vger.kernel.org, linux-safety@lists.elisa.tech,
	Lukas Bulwahn <lukas.bulwahn@gmail.com>
Subject: [PATCH] x86/mm: drop superfluous initialization
Date: Mon, 28 Sep 2020 12:00:04 +0200	[thread overview]
Message-ID: <20200928100004.25674-1-lukas.bulwahn@gmail.com> (raw)

It is not required to initialize the local variable start in
memory_map_top_down(), as the variable will be initialized in any path
before it is used.

make clang-analyzer on x86_64 tinyconfig reports:

  arch/x86/mm/init.c:612:15: warning: Although the value stored to 'start' \
  is used in the enclosing expression, the value is never actually read \
  from 'start' [clang-analyzer-deadcode.DeadStores]

Compilers will detect this superfluous assignment and optimize that
expression anyway. So, the resulting binary is identical before and after
the change.

Drop this superfluous assignment to make clang-analyzer happy.

No functional change.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
---
applies cleanly on v5.9-rc7 and next-20200925

Dave, Andy, Peter, please pick this minor non-urgent clean-up patch.

I quickly confirmed that the binary did not change with this change to the
source code; the hash of init.o remained the same before and after the change.

So, in my setup:
  md5sum arch/x86/mm/init.o
  b26f6380760f32d2ef2c7525301eebd3  init.o

linux-safety, please verify and validate this change.

 arch/x86/mm/init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index c7a47603537f..5632f02146ca 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -609,7 +609,7 @@ static void __init memory_map_top_down(unsigned long map_start,
 	step_size = PMD_SIZE;
 	max_pfn_mapped = 0; /* will get exact value next */
 	min_pfn_mapped = real_end >> PAGE_SHIFT;
-	last_start = start = real_end;
+	last_start = real_end;
 
 	/*
 	 * We start from the top (end of memory) and go to the bottom.
-- 
2.17.1


WARNING: multiple messages have this Message-ID (diff)
From: Lukas Bulwahn <lukas.bulwahn@gmail.com>
To: Dave Hansen <dave.hansen@linux.intel.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	Nathan Chancellor <natechancellor@gmail.com>,
	Nick Desaulniers <ndesaulniers@google.com>,
	linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com,
	kernel-janitors@vger.kernel.org, linux-safety@lists.elisa.tech,
	Lukas Bulwahn <lukas.bulwahn@gmail.com>
Subject: [PATCH] x86/mm: drop superfluous initialization
Date: Mon, 28 Sep 2020 10:00:04 +0000	[thread overview]
Message-ID: <20200928100004.25674-1-lukas.bulwahn@gmail.com> (raw)

It is not required to initialize the local variable start in
memory_map_top_down(), as the variable will be initialized in any path
before it is used.

make clang-analyzer on x86_64 tinyconfig reports:

  arch/x86/mm/init.c:612:15: warning: Although the value stored to 'start' \
  is used in the enclosing expression, the value is never actually read \
  from 'start' [clang-analyzer-deadcode.DeadStores]

Compilers will detect this superfluous assignment and optimize that
expression anyway. So, the resulting binary is identical before and after
the change.

Drop this superfluous assignment to make clang-analyzer happy.

No functional change.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
---
applies cleanly on v5.9-rc7 and next-20200925

Dave, Andy, Peter, please pick this minor non-urgent clean-up patch.

I quickly confirmed that the binary did not change with this change to the
source code; the hash of init.o remained the same before and after the change.

So, in my setup:
  md5sum arch/x86/mm/init.o
  b26f6380760f32d2ef2c7525301eebd3  init.o

linux-safety, please verify and validate this change.

 arch/x86/mm/init.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
index c7a47603537f..5632f02146ca 100644
--- a/arch/x86/mm/init.c
+++ b/arch/x86/mm/init.c
@@ -609,7 +609,7 @@ static void __init memory_map_top_down(unsigned long map_start,
 	step_size = PMD_SIZE;
 	max_pfn_mapped = 0; /* will get exact value next */
 	min_pfn_mapped = real_end >> PAGE_SHIFT;
-	last_start = start = real_end;
+	last_start = real_end;
 
 	/*
 	 * We start from the top (end of memory) and go to the bottom.
-- 
2.17.1

             reply	other threads:[~2020-09-28 10:00 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-28 10:00 Lukas Bulwahn [this message]
2020-09-28 10:00 ` [PATCH] x86/mm: drop superfluous initialization Lukas Bulwahn
2020-09-28 17:59 ` Dave Hansen
2020-09-28 17:59   ` Dave Hansen
2020-09-29  8:42   ` Lukas Bulwahn
2020-09-29  8:42     ` Lukas Bulwahn
2020-09-29  8:42     ` Lukas Bulwahn
2020-11-20 11:51 ` [tip: x86/cleanups] x86/mm: Declare 'start' variable where it is used tip-bot2 for Lukas Bulwahn

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