[v3,1/5] kbuild: add test-{le,ge,lt,gt} macros
Commit Message
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 $$?),0)
This is more expensive than using built-in functions since it forks a
process.
If we know the two have the same number of digits, we can do better.
This commit adds four macros, test-le, test-ge, test-lt, test-gt.
$(call test-lt, A, B) is evaluated to 'y' if A is less than B, or
empty otherwise. This will replace $(call shell test A -lt B).
Again, the limitation is that A and B must have the same number of
digits because these macros are based on $(sort ) function.
$(call test-lt, 1, 9) --> y (Works!)
$(call test-lt, 10, 9) --> y (Not work...)
To make the latter work, you need to add '0' prefix to align the number
of digits:
$(call test-lt, 10, 09) --> empty (Works!)
Actually, we can live with this limitation in many places. As for the
example above, we know $(CONFIG_LLD_VERSION) is 6-digits because the
minimal supported version of LLVM is 11.0.0 (or CONFIG_LLD_VERSION=0
if the linker is not LLD, this case also works.)
So, the shell invocation can be replaced with more efficient code:
ifeq ($(call test-lt, $(CONFIG_LLD_VERSION), 130000),y)
Of course, this assumption will break when LLVM 100 is released, but it
will be far in the future.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
---
Changes in v3:
- Ensure the given parameters are not empty
Makefile | 2 +-
arch/riscv/Makefile | 2 +-
arch/x86/Makefile | 2 +-
scripts/Kbuild.include | 10 ++++++++++
4 files changed, 13 insertions(+), 3 deletions(-)
@@ -986,7 +986,7 @@ KBUILD_LDFLAGS += -mllvm -import-instr-limit=5
# Check for frame size exceeding threshold during prolog/epilog insertion
# when using lld < 13.0.0.
ifneq ($(CONFIG_FRAME_WARN),0)
-ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 130000; echo $$?),0)
+ifeq ($(call test-lt, $(CONFIG_LLD_VERSION), 130000),y)
KBUILD_LDFLAGS += -plugin-opt=-warn-stack-size=$(CONFIG_FRAME_WARN)
endif
endif
@@ -37,7 +37,7 @@ else
endif
ifeq ($(CONFIG_LD_IS_LLD),y)
-ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 150000; echo $$?),0)
+ifeq ($(call test-lt, $(CONFIG_LLD_VERSION), 150000),y)
KBUILD_CFLAGS += -mno-relax
KBUILD_AFLAGS += -mno-relax
ifndef CONFIG_AS_IS_LLVM
@@ -211,7 +211,7 @@ endif
KBUILD_LDFLAGS += -m elf_$(UTS_MACHINE)
ifdef CONFIG_LTO_CLANG
-ifeq ($(shell test $(CONFIG_LLD_VERSION) -lt 130000; echo $$?),0)
+ifeq ($(call test-lt, $(CONFIG_LLD_VERSION), 130000),y)
KBUILD_LDFLAGS += -plugin-opt=-stack-alignment=$(if $(CONFIG_X86_32),4,8)
endif
endif
@@ -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 $@)