[PATCH] Makefile: fix u-boot-initial-env target if lto is enabled

[Tom Rini]

On Tue, Oct 18, 2022 at 07:48:27PM +0200, Max Krummenacher wrote:
> From: Max Krummenacher <max.krummenacher at toradex.com>
> 
> With LTO enabled the U-Boot initial environment is no longer stored
> in an easy accessible section in env/common.o. I.e. the section name
> changes from build to build, its content maybe compressed and it is
> annotated with additional data.
> 
> For GCC adding the option '-ffat-lto-objects' when compiling common.o
> adds additionally the traditional sections in the object file and
> 'make u-boot-initial-env' would work also for the LTO enabled case.
> However clang doesn't have that option.
> 
> Fix this by recompiling common.o into a object file only used for
> the creation of u-boot-initial-env if LTO is enabled.
> 
> See also:
> https://lore.kernel.org/all/927b122e-1f62-e790-f5ca-30bae4332c77@foss.st.com/
> 
> Signed-off-by: Max Krummenacher <max.krummenacher at toradex.com>
> 
> ---
> 
>  Makefile | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index 3866cc62f9a..cd45c720d23 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -2451,9 +2451,17 @@ endif
>  	$(Q)$(MAKE) -f $(srctree)/scripts/Makefile.modpost
>  
>  quiet_cmd_genenv = GENENV  $@
> +ifeq ($(LTO_ENABLE),y)
> +cmd_genenv = $(CC) $(filter-out $(LTO_CFLAGS),$(c_flags)) -c -o env/initial_env.o env/common.c; \
> +	$(OBJCOPY) --dump-section .rodata.default_environment=$@ env/initial_env.o; \
> +	sed --in-place -e 's/\x00/\x0A/g' $@; sed --in-place -e '/^\s*$$/d' $@; \
> +	sort --field-separator== -k1,1 --stable $@ -o $@; \
> +	rm -f env/initial_env.o env/initial_env.su
> +else
>  cmd_genenv = $(OBJCOPY) --dump-section .rodata.default_environment=$@ env/common.o; \
>  	sed --in-place -e 's/\x00/\x0A/g' $@; sed --in-place -e '/^\s*$$/d' $@; \
>  	sort --field-separator== -k1,1 --stable $@ -o $@
> +endif
>  
>  u-boot-initial-env: u-boot.bin
>  	$(call if_changed,genenv)

Can we pipe the output instead of making a new object file? Maybe not,
in a portable way it seems. But, I'm not sure the above respects using
O= as well so that does need to be checked and fixed if so.

-- 
Tom
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