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

[Jeroen Hofstee <jeroen@myspectrum.nl>]

Hello Masahiro,

On 09/30/2013 10:01 AM, Masahiro Yamada wrote:
> 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.
>
>

I tried to google this a bit, one thing I found was
http://sourceware.org/bugzilla/show_bug.cgi?id=5210, but I fail
to (easily) find a reliable gcc reference. Perhaps we should
file a bug? -Werror doesn't work with /dev/null when
-fstack-usage is not supported...

I cannot comment on your concern regarding Kbuild, since I
am unaware of its internals. I just suggested above since
it would be a cleaner approach (if it worked...).

Regards,
Jeroen