Re: [PATCH for-4.7] xen/build: Fix build with Clang

[Doug Goldstein <cardoe@cardoe.com>]

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On 4/7/16 2:21 PM, Jan Beulich wrote:
>>>> On 07.04.16 at 21:16, <andrew.cooper3@citrix.com> wrote:
>> On 07/04/16 20:12, Jan Beulich wrote:
>>>>>> On 07.04.16 at 20:46, <andrew.cooper3@citrix.com> wrote:
>>>> --- a/xen/Rules.mk
>>>> +++ b/xen/Rules.mk
>>>> @@ -50,9 +50,15 @@ ALL_OBJS-$(CONFIG_X86)   += $(BASEDIR)/crypto/built_in.o
>>>>  CFLAGS += -nostdinc -fno-builtin -fno-common
>>>>  CFLAGS += -Werror -Wredundant-decls -Wno-pointer-arith
>>>>  CFLAGS += -pipe -g -D__XEN__ -include $(BASEDIR)/include/xen/config.h
>>>> -CFLAGS += -Wa,--strip-local-absolute
>>>>  CFLAGS += '-D__OBJECT_FILE__="$@"'
>>>>  
>>>> +ifneq ($(clang),y)
>>>> +# Clang doesn't understand this command line argument, and doesn't appear to
>>>> +# have an suitable alternative.  The resulting compiled binary does function,
>>>> +# but has an excessively large symbol table.
>>>> +CFLAGS += -Wa,--strip-local-absolute
>>>> +endif
>>> Well, that's the brute force undo-it-altogether-for-clang approach
>>> that I think Doug had also considered. You may have seen the
>>> discussion (on irc iirc) - I'd really like to see the option still getting
>>> passed to gas (for all the .S files) even when using clang. Would
>>> that really be hard to arrange for?
>>
>> That won't fix the fact that all the .c files which include
>> cpufeatureset.h also gets the absolute symbols, to allow the
>> alternatives() blocks to compile.
> 
> That's understood.
> 
>> It will complicate the clang build quite a bit, and won't make much of a
>> dent on the symbol table bloat.
> 
> While this I'm unclear about: Istr Doug mentioning that simply
> adding the option in suitable for to AFLAGS would do.
> 
> Jan
> 

I was trying to do exactly what you mentioned where we still passed it
to gas and didn't pass it to llvm but unfortunately at some point the
flags get combined together and passed to llvm and fails.

-- 
Doug Goldstein


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