linux-kernel - [PATCH] Drop -Wdeclaration-after-statement

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Message-ID: <YhiQPhsoODiXRAPy@localhost.localdomain>
Date:   Fri, 25 Feb 2022 11:15:58 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     akpm@...ux-foundation.org
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] Drop -Wdeclaration-after-statement

Putting declarations before statement is relict of single pass compiler
era. It was necessary to allocate stack slots before generating code.

Recently added static_assert() is a declaration. -Wdeclaration-after-statement
prevents its placement anywhere in the code for no reason.

Placing variable declarations in the beginning of the block increases
variable "LOC lifetime" so to speak and chances that it will be misused.
This is very low probability bug but still. Declaring variables right
before first use will make "LOC lifetime" smaller.

	{
		int x;
		[x is misused due to a typo]
		f(x);	// first correct use
	}

vs

	{
		[can't misuse undeclared variable]
		int x;
		f(x);	// first correct use
	}

Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---

 Makefile                          |    3 ---
 arch/arm64/kernel/vdso32/Makefile |    1 -
 tools/power/acpi/Makefile.config  |    1 -
 tools/power/cpupower/Makefile     |    1 -
 tools/scripts/Makefile.include    |    1 -
 5 files changed, 7 deletions(-)

--- a/Makefile
+++ b/Makefile
@@ -933,9 +933,6 @@ endif
 # arch Makefile may override CC so keep this after arch Makefile is included
 NOSTDINC_FLAGS += -nostdinc
 
-# warn about C99 declaration after statement
-KBUILD_CFLAGS += -Wdeclaration-after-statement
-
 # Variable Length Arrays (VLAs) should not be used anywhere in the kernel
 KBUILD_CFLAGS += -Wvla
 
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -71,7 +71,6 @@ VDSO_CFLAGS += -Wall -Wundef -Wstrict-prototypes -Wno-trigraphs \
                -std=gnu89
 VDSO_CFLAGS  += -O2
 # Some useful compiler-dependent flags from top-level Makefile
-VDSO_CFLAGS += $(call cc32-option,-Wdeclaration-after-statement,)
 VDSO_CFLAGS += $(call cc32-option,-Wno-pointer-sign)
 VDSO_CFLAGS += -fno-strict-overflow
 VDSO_CFLAGS += $(call cc32-option,-Werror=strict-prototypes)
--- a/tools/power/acpi/Makefile.config
+++ b/tools/power/acpi/Makefile.config
@@ -63,7 +63,6 @@ OPTIMIZATION := $(call cc-supports,-Os,-O2)
 
 WARNINGS := -Wall
 WARNINGS += $(call cc-supports,-Wstrict-prototypes)
-WARNINGS += $(call cc-supports,-Wdeclaration-after-statement)
 
 KERNEL_INCLUDE := $(OUTPUT)include
 ACPICA_INCLUDE := $(srctree)/../../../drivers/acpi/acpica
--- a/tools/power/cpupower/Makefile
+++ b/tools/power/cpupower/Makefile
@@ -118,7 +118,6 @@ OPTIMIZATION := $(call cc-supports,-Os,-O2)
 
 WARNINGS := -Wall -Wchar-subscripts -Wpointer-arith -Wsign-compare
 WARNINGS += $(call cc-supports,-Wno-pointer-sign)
-WARNINGS += $(call cc-supports,-Wdeclaration-after-statement)
 WARNINGS += -Wshadow
 
 override CFLAGS += -DVERSION=\"$(VERSION)\" -DPACKAGE=\"$(PACKAGE)\" \
--- a/tools/scripts/Makefile.include
+++ b/tools/scripts/Makefile.include
@@ -21,7 +21,6 @@ endif
 # Include saner warnings here, which can catch bugs:
 #
 EXTRA_WARNINGS := -Wbad-function-cast
-EXTRA_WARNINGS += -Wdeclaration-after-statement
 EXTRA_WARNINGS += -Wformat-security
 EXTRA_WARNINGS += -Wformat-y2k
 EXTRA_WARNINGS += -Winit-self