[PATCH v3 1/5] kbuild: add test-{le,ge,lt,gt} macros

[Masahiro Yamada <masahiroy@kernel.org>]

Because GNU Make is handle strings, it is very hard to perform math in
Makefiles.

When we compare two integers, we invokes shell. One example is in the
top Makefile:

  ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 130000; echo $$?),0)

This is more expensive than using built-in functions since it forks a
process.

If we know the two have the same number of digits, we can do better.

This commit adds four macros, test-le, test-ge, test-lt, test-gt.

$(call test-lt, A, B) is evaluated to 'y' if A is less than B, or
empty otherwise. This will replace $(call shell test A -lt B).

Again, the limitation is that A and B must have the same number of
digits because these macros are based on $(sort ) function.

  $(call test-lt, 1, 9)    -->  y        (Works!)
  $(call test-lt, 10, 9)   -->  y        (Not work...)

To make the latter work, you need to add '0' prefix to align the number
of digits:

  $(call test-lt, 10, 09)  -->  empty    (Works!)

Actually, we can live with this limitation in many places. As for the
example above, we know $(CONFIG_LLD_VERSION) is 6-digits because the
minimal supported version of LLVM is 11.0.0 (or CONFIG_LLD_VERSION=0
if the linker is not LLD, this case also works.)

So, the shell invocation can be replaced with more efficient code:

  ifeq ($(call test-lt, $(CONFIG_LLD_VERSION), 130000),y)

Of course, this assumption will break when LLVM 100 is released, but it
will be far in the future.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
---

Changes in v3:
  - Ensure the given parameters are not empty

 Makefile               |  2 +-
 arch/riscv/Makefile    |  2 +-
 arch/x86/Makefile      |  2 +-
 scripts/Kbuild.include | 10 ++++++++++
 4 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/Makefile b/Makefile
index 6f846b1f2618..eb80332f7b51 100644
--- a/Makefile
+++ b/Makefile
@@ -986,7 +986,7 @@ KBUILD_LDFLAGS += -mllvm -import-instr-limit=5
 # Check for frame size exceeding threshold during prolog/epilog insertion
 # when using lld < 13.0.0.
 ifneq ($(CONFIG_FRAME_WARN),0)
-ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 130000; echo $$?),0)
+ifeq ($(call test-lt, $(CONFIG_LLD_VERSION), 130000),y)
 KBUILD_LDFLAGS	+= -plugin-opt=-warn-stack-size=$(CONFIG_FRAME_WARN)
 endif
 endif
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 0d13b597cb55..faf2c2177094 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -37,7 +37,7 @@ else
 endif
 
 ifeq ($(CONFIG_LD_IS_LLD),y)
-ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 150000; echo $$?),0)
+ifeq ($(call test-lt, $(CONFIG_LLD_VERSION), 150000),y)
 	KBUILD_CFLAGS += -mno-relax
 	KBUILD_AFLAGS += -mno-relax
 ifndef CONFIG_AS_IS_LLVM
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 415a5d138de4..e72c7a49cd59 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -211,7 +211,7 @@ endif
 KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)
 
 ifdef CONFIG_LTO_CLANG
-ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 130000; echo $$?),0)
+ifeq ($(call test-lt, $(CONFIG_LLD_VERSION), 130000),y)
 KBUILD_LDFLAGS	+= -plugin-opt=-stack-alignment=$(if $(CONFIG_X86_32),4,8)
 endif
 endif
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index cbe28744637b..4b8cf464b53b 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -11,6 +11,16 @@ space   := $(empty) $(empty)
 space_escape := _-_SPACE_-_
 pound := \#
 
+###
+# Comparison macros.
+# Usage: $(call test-le, A, B)
+# works like shell's "test A -le B", use with care bacause it is ASCII sort.
+# If A and B have the same number of digits, it works as expected.
+test-le = $(and $(strip $1),$(strip $2),$(filter $1, $(firstword $(sort $1 $2))),y)
+test-ge = $(call test-le, $2, $1)
+test-lt = $(and $(strip $1),$(strip $2),$(filter-out $2, $(firstword $(sort $1 $2))),y)
+test-gt = $(call test-lt, $2, $1)
+
 ###
 # Name of target with a '.' as filename prefix. foo/bar.o => foo/.bar.o
 dot-target = $(dir $@).$(notdir $@)
-- 
2.34.1