Messages in this thread | | | From | Masahiro Yamada <> | Date | Wed, 21 Feb 2018 21:57:03 +0900 | Subject | Re: [PATCH 00/23] kconfig: move compiler capability tests to Kconfig |
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2018-02-21 19:52 GMT+09:00 Arnd Bergmann <arnd@arndb.de>: > On Wed, Feb 21, 2018 at 11:20 AM, Masahiro Yamada > <yamada.masahiro@socionext.com> wrote: >> 2018-02-21 18:56 GMT+09:00 Arnd Bergmann <arnd@arndb.de>: >>> On Wed, Feb 21, 2018 at 8:38 AM, Masahiro Yamada >>> <yamada.masahiro@socionext.com> wrote: >>>> 2018-02-20 0:18 GMT+09:00 Ulf Magnusson <ulfalizer@gmail.com>: >> >> 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
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