[U-Boot] [PATCH v2 4/4] kbuild: improve Kbuild speed

[Simon Glass]

On 27 February 2014 21:23, Masahiro Yamada <yamada.m at jp.panasonic.com>wrote:

> Kbuild brought about many advantages for us but a significant
> performance regression was reported by Simon Glass.
>
> After some discussions and analysis, it turned out
> its main cause is in $(call cc-option,...).
>
> Historically, U-Boot parses all config.mk
> (arch/*/config.mk and board/*/config.mk)
> every time descending into subdirectories.
> That means cc-options are evaluated over and over again.
>
> $(call cc-option,...) is useful but costly.
> So we want to evaluate them only in ./Makefile
> and spl/Makefile and export compiler flags.
>
> This commit changes the build system as follows:
>
>   - Modify scripts/Makefile.build to not include config.mk
>     Instead, add $(PLATFORM_CPPFLAGS) to asflags-y, ccflags-y,
>     cppflags-y.
>
>   - Export many variables
>     Going forward, Kbuild will not parse config.mk files
>     when it descends into subdirectories.
>     If we want to set variables in config.mk and use them
>     in subdirectories, they must be exported.
>
>     This is the list of variables to get exported:
>       PLATFORM_CPPFLAGS
>       CPUDIR
>       BOARDDIR
>       OBJCOPYFLAGS
>       LDFLAGS
>       LDFLAGS_FINAL
>         (used in nand_spl/board/*/*/Makefile)
>       CONFIG_STANDALONE_LOAD_ADDR
>         (used in examples/standalone/Makefile)
>       SYM_PREFIX
>         (used in examples/standalone/Makefile)
>       RELFLAGS
>         (used in examples/standalone/Makefile)
>
>   - Delete CPPFLAGS
>     This variable has been replaced with PLATFORM_CPPFLAGS
>
>   - Copy gcclibdir from example/standalone/Makefile
>     to arch/sparc/config.mk
>     The reference in CONFIG_STANDALONE_LOAD_ADDR must be
>     resolved before it is exported.
>
> Signed-off-by: Masahiro Yamada <yamada.m at jp.panasonic.com>
> Reported-by: Simon Glass <sjg at chromium.org>
> Tested-by: Stephen Warren <swarren at nvidia.com>
>

Acked-by: Simon Glass <sjg at chromium.org>

Tested only on sandbox:

Tested-by: Simon Glass <sjg at chromium.org>