[U-Boot] [PATCH] config.mk: enable -fstack-usage only when it is desired

[Masahiro Yamada]

Hello Jeroen,

> diff --git a/config.mk b/config.mk
> index 48913f6..177f685 100644
> --- a/config.mk
> +++ b/config.mk
> @@ -117,7 +117,7 @@ CC_TEST_OFILE := 
> $(OBJTREE)/include/generated/cc_test_file.o
>   -include $(CC_OPTIONS_CACHE_FILE)
> 
>   cc-option-sys = $(shell mkdir -p $(dir $(CC_TEST_OFILE)); \
> -               if $(CC) $(CFLAGS) $(1) -S -xc /dev/null -o 
> $(CC_TEST_OFILE) \
> +               if $(CC) -Werror $(CFLAGS) $(1) -S -xc /dev/null -o 
> $(CC_TEST_OFILE) \
>                  > /dev/null 2>&1; then \
>                  echo 'CC_OPTIONS += $(strip $1)' >> 
> $(CC_OPTIONS_CACHE_FILE); \
>                  echo "$(1)"; fi)



It looks like this was already suggested by Tom too.
See http://patchwork.ozlabs.org/patch/183174/

I tested this patch but unfortunatelly it did not work. 


I downloaded bfin-linux-gcc 4.6.3 from
ftp://ftp.kernel.org/pub/tools/crosstool/index.html

I added -Werror to config.mk and I tried:

    CROSS_COMPILE=bfin-linux- ./MAKEALL -a blackfin

The log message was still sprinkled with lots of warnings like
warning: -fstack-usage not supported for this target [enabled by default]

So, I looked into it more closely and
I found gcc can compile the input file /dev/null successfully
even if -fstack-usage is not supported.


    $ bfin-uclinux-gcc -fstack-usage -S -xc /dev/null 
    $ echo $?
    0
    $ bfin-uclinux-gcc -Werror -fstack-usage -S -xc /dev/null 
    $ echo $?
    0



Instead of /dev/null, I prepared a very simple C source code as an input.

    $ cat test.c
    int test(void)
    {
        return 0;
    }
    $ bfin-uclinux-gcc -fstack-usage -S -xc test.c
    test.c: In function 'test':
    test.c:4:1: warning: -fstack-usage not supported for this target [enabled by default]
    $ echo $?
    0
    $ bfin-uclinux-gcc -fstack-usage -Werror -S -xc test.c
    test.c: In function 'test':
    test.c:4:1: error: -fstack-usage not supported for this target [-Werror]
    cc1: all warnings being treated as errors
    $ echo $?
    1

This time we can detect unsupported -fstack-usage by the exit status.

So, along with -Werror, I think /dev/null should also be replaced
with some _REAL_ C source file.
But my concern about this treak is we might go far from Kbuild.
In Linux Kernel, cc-option is impilemented in scripts/Kbuild.include.
It uses /dev/null as input.
I wish U-Boot would someday adopt (not nessarily the same but very
similar) Kbuild.

If you see Linux Kernel top Makefile,
many of optional CFLAGS are provided thru cc-option and
also can be turned on/off by CONFIG_ switch.

That is one reason I suggested to introduce CONFIG_CC_STACKUSAGE option.
But this is just my opinion and I would not necessarily stick to this idea.
Please feel free to suggest your thought.


Best Regards
Masahiro Yamada