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kernel_module, sample_package: correctly forward Buildroot -O and -g flags

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readme: improve optimization documentation
This commit is contained in:
Ciro Santilli
2018-04-17 14:51:43 +01:00
parent ffa430eef9
commit 50f2518656
5 changed files with 83 additions and 50 deletions
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36
README.adoc
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@@ -425,6 +425,18 @@ Not all packages have an alias, when they don't, just use the form:
./build -- <pkg>-reconfigure
....
==== Rebuild a package with different build options
For example, if you decide to <<enable-compiler-optimizations>> after an initial build is finished, you must first clean the build before rebuilding:
....
./build -B 'BR2_OPTIMIZE_3=y' kernel_module-dirclean kernel_module-reconfigure
....
as explained at: https://buildroot.org/downloads/manual/manual.html#rebuild-pkg
The clean is necessary because the source files didn't change, so `make` would just check the timestamps and not build anything.
[[retype]]
=== Don't retype arguments all the time
@@ -4538,9 +4550,29 @@ You will likely want to change that to:
BR2_OPTIMIZE_3=y
....
and do a full rebuild.
Our link:kernel_module/user[] package correctly forwards the Buildroot options to the build with `$(TARGET_CONFIGURE_OPTS)`, so you don't have to do any extra work.
TODO is it possible to compile a single package with optimizations enabled? In any case, this wouldn't be very representative, since calls to an unoptimized libc will also have an impact on performance. Kernel-wise it should be fine though due to: <<kernel-o0>>
Don't forget to do that if you are <<add-new-buildroot-packages,adding a new package>> with your own build system.
Then, you have two choices:
* if you already have a full `-O0` build, you can choose to rebuild just your package of interest to save some time as described at: <<rebuild-a-package-with-different-build-options>>
+
....
./build -B 'BR2_OPTIMIZE_3=y' kernel_module-dirclean kernel_module-reconfigure
....
+
However, this approach might not be representative since calls to an unoptimized libc and other libraries will have a negative performance impact.
+
Maybe you can get away with rebuilding libc, but I'm not sure that it will work properly.
+
Kernel-wise it should be fine though due to: <<kernel-o0>>
* <<clean-the-build,clean the build>> and rebuild from scratch:
+
....
mv out out~
./build -B 'BR2_OPTIMIZE_3=y'
....
=== Find Buildroot options with make menuconfig

2
kernel_module/external.mk
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@@ -13,7 +13,7 @@ ifeq ($(BR2_PACKAGE_OPENBLAS),y)
endif
define KERNEL_MODULE_BUILD_CMDS
$(MAKE) -C '$(@D)/user' BR2_PACKAGE_OPENBLAS="$(BR2_PACKAGE_OPENBLAS)" CC="$(TARGET_CC)" LD="$(TARGET_LD)"
$(MAKE) -C '$(@D)/user' $(TARGET_CONFIGURE_OPTS) BR2_PACKAGE_OPENBLAS="$(BR2_PACKAGE_OPENBLAS)"
endef
define KERNEL_MODULE_INSTALL_TARGET_CMDS

2
kernel_module/user/Makefile
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@@ -1,6 +1,6 @@
.PHONY: all clean
CFLAGS_EXTRA ?= -ggdb3 -fopenmp -O0 -std=c99 -Wall -Werror -Wextra
CFLAGS_EXTRA ?= -fopenmp -std=c99 -Wall -Werror -Wextra
IN_EXT ?= .c
LIBS :=
OUT_EXT ?= .out

2
sample_package/Makefile
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@@ -1,6 +1,6 @@
.PHONY: all clean
CFLAGS_EXTRA ?= -ggdb3 -fopenmp -O0 -std=c99 -Wall -Werror -Wextra
CFLAGS_EXTRA ?= -fopenmp -std=c99 -Wall -Werror -Wextra
IN_EXT ?= .c
LIBS :=
OUT_EXT ?= .out

3
sample_package/external.mk
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@@ -10,7 +10,8 @@ SAMPLE_PACKAGE_SITE_METHOD = local
define SAMPLE_PACKAGE_BUILD_CMDS
# D contains the source code of this package.
$(MAKE) -C '$(@D)' CC="$(TARGET_CC)" LD="$(TARGET_LD)"
# TARGET_CONFIGURE_OPTS contains several common options such as CFLAGS and LDFLAGS.
$(MAKE) -C '$(@D)' $(TARGET_CONFIGURE_OPTS)
endef
define SAMPLE_PACKAGE_INSTALL_TARGET_CMDS