2018-02-21 19:52 GMT+09:00 Arnd Bergmann [off-list ref]:

On Wed, Feb 21, 2018 at 11:20 AM, Masahiro Yamada
[off-list ref] wrote:

quoted

2018-02-21 18:56 GMT+09:00 Arnd Bergmann [off-list ref]:

quoted

On Wed, Feb 21, 2018 at 8:38 AM, Masahiro Yamada
[off-list ref] wrote:

quoted

2018-02-20 0:18 GMT+09:00 Ulf Magnusson [off-list ref]:

Let me clarify my concern.

When we test the compiler flag, is there a case
where a particular flag depends on -m{32,64} ?

For example, is there a compiler that supports -fstack-protector
for 64bit mode, but unsupports it for 32bit mode?

  $(cc-option -m32)                     ->  y
  $(cc-option -m64)                     ->  y
  $(cc-option -fstack-protector)        ->  y
  $(cc-option -m32 -fstack-protector)   ->  n
  $(cc-option -m64 -fstack-protector)   ->  y

I guess this is unlikely to happen,
but I am not whether it is zero possibility.

If this could happen,
$(cc-option ) must be evaluated together with
correct bi-arch option (either -m32 or -m64).


Currently, -m32/-m64 is specified in Makefile,
but we are moving compiler tests to Kconfig
and, CONFIG_64BIT can be dynamically toggled in Kconfig.

I don't think it can happen for this particular combination (stack protector
and word size), but I'm sure we'll eventually run into options that
need to be tested in combination. For the current CFLAGS_KERNEL
setting, we definitely have the case of needing the variables to be
evaluated in a specific order.

I was thinking of how we can handle complex cases
in the current approach.



(Case 1)

Compiler flag -foo and -bar interacts, so
we also need to check the combination of the two.


config CC_HAS_FOO
        def_bool $(cc-option -foo)

config CC_HAS_BAR
        def_bool $(cc-option -bar)

config CC_HAS_FOO_WITH_BAR
        def_bool $(cc-option -foo -bar)



(Case 2)
Compiler flag -foo is sensitive to word-size.
So, we need to test this option together with -m32/-m64.
User can toggle CONFIG_64BIT, like i386/x86_64.


config CC_NEEDS_M64
          def_bool $(cc-option -m64) && 64BIT

config CC_NEEDS_M32
          def_bool $(cc-option -m32) && !64BIT

config CC_HAS_FOO
         bool
         default $(cc-option -m64 -foo) if CC_NEEDS_M64
         default $(cc-option -m32 -foo) if CC_NEEDS_M32
         default $(cc-option -foo)



(Case 3)
Compiler flag -foo is sensitive to endian-ness.


config CC_NEEDS_BIG_ENDIAN
          def_bool $(cc-option -mbig-endian) && CPU_BIG_ENDIAN

config CC_NEEDS_LITTLE_ENDIAN
          def_bool $(cc-option -mlittle-endian) && CPU_LITTLE_ENDIAN

config CC_HAS_FOO
         bool
         default $(cc-option -mbig-endian -foo) if CC_NEEDS_BIG_ENDIAN
         default $(cc-option -mlittle-endian -foo) if CC_NEEDS_LITTLE_ENDIAN
         default $(cc-option -foo)




Hmm, I think I can implement those somehow.
But, I hope we do not have many instances like this...


If you know more naive cases, please share your knowledge.

Thanks!


-- 
Best Regards
Masahiro Yamada