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

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