kbuild: raise the minimum GNU Make requirement to 4.0

RHEL/CentOS 7, popular distributions that install GNU Make 3.82, reached
EOM/EOL on June 30, 2024. While you may get extended support, it is a
good time to raise the minimum GNU Make version.

The new requirement, GNU Make 4.0, was released in October, 2013.

I did not touch the Makefiles under tools/ because I do not know the
requirements for building tools. I do not find any GNU Make version
checks under tools/.

Signed-off-by: Masahiro Yamada <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>

Author: masahir0y

Documentation/process/changes.rst

@@ -33,7 +33,7 @@ GNU C                  5.1              gcc --version
 Clang/LLVM (optional)  13.0.1           clang --version
 Rust (optional)        1.78.0           rustc --version
 bindgen (optional)     0.65.1           bindgen --version
-GNU make               3.82             make --version
+GNU make               4.0              make --version
 bash                   4.2              bash --version
 binutils               2.25             ld -v
 flex                   2.5.35           flex --version
@@ -111,7 +111,7 @@ It depends on ``libclang``.
 Make
 ----
 
-You will need GNU make 3.82 or later to build the kernel.
+You will need GNU make 4.0 or later to build the kernel.
 
 Bash
 ----

Makefile

@@ -11,8 +11,8 @@ NAME = Baby Opossum Posse
 # Comments in this file are targeted only to the developer, do not
 # expect to learn how to build the kernel reading this file.
 
-ifeq ($(filter undefine,$(.FEATURES)),)
-$(error GNU Make >= 3.82 is required. Your Make version is $(MAKE_VERSION))
+ifeq ($(filter output-sync,$(.FEATURES)),)
+$(error GNU Make >= 4.0 is required. Your Make version is $(MAKE_VERSION))
 endif
 
 $(if $(filter __%, $(MAKECMDGOALS)), \
@@ -93,15 +93,7 @@ endif
 
 # If the user is running make -s (silent mode), suppress echoing of
 # commands
-# make-4.0 (and later) keep single letter options in the 1st word of MAKEFLAGS.
-
-ifeq ($(filter 3.%,$(MAKE_VERSION)),)
-short-opts := $(firstword -$(MAKEFLAGS))
-else
-short-opts := $(filter-out --%,$(MAKEFLAGS))
-endif
-
-ifneq ($(findstring s,$(short-opts)),)
+ifneq ($(findstring s,$(firstword -$(MAKEFLAGS))),)
 quiet=silent_
 override KBUILD_VERBOSE :=
 endif
@@ -201,14 +193,6 @@ ifneq ($(words $(subst :, ,$(abs_srctree))), 1)
 $(error source directory cannot contain spaces or colons)
 endif
 
-ifneq ($(filter 3.%,$(MAKE_VERSION)),)
-# 'MAKEFLAGS += -rR' does not immediately become effective for GNU Make 3.x
-# We need to invoke sub-make to avoid implicit rules in the top Makefile.
-need-sub-make := 1
-# Cancel implicit rules for this Makefile.
-$(this-makefile): ;
-endif
-
 export sub_make_done := 1
 
 endif # sub_make_done

scripts/Kbuild.include

@@ -68,7 +68,7 @@ kbuild-file = $(or $(wildcard $(src)/Kbuild),$(src)/Makefile)
 # Read a file, replacing newlines with spaces
 #
 # Make 4.2 or later can read a file by using its builtin function.
-ifneq ($(filter-out 3.% 4.0 4.1, $(MAKE_VERSION)),)
+ifneq ($(filter-out 4.0 4.1, $(MAKE_VERSION)),)
 read-file = $(subst $(newline),$(space),$(file < $1))
 else
 read-file = $(shell cat $1 2>/dev/null)