Re: [BUG] Build error for 4.15-rc3 kernel caused by patch "kbuild: Add a cache for generated variables"

[Masahiro Yamada]

2017-12-18 23:56 GMT+09:00 Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx>:
> 2017-12-17 7:35 GMT+09:00 Yang Shi <yang.s@xxxxxxxxxxxxxxx>:
>> Hi folks,
>>
>> I just upgraded gcc to 6.4 on my centos 7 machine by Arnd's suggestion. But,
>> I ran into the below compile error with 4.15-rc3 kernel:
>>
>> In file included from ./include/uapi/linux/uuid.h:21:0,
>>                  from ./include/linux/uuid.h:19,
>>                  from ./include/linux/mod_devicetable.h:12,
>>                  from scripts/mod/devicetable-offsets.c:2:
>> ./include/linux/string.h:8:20: fatal error: stdarg.h: No such file or
>> directory
>>  #include <stdarg.h>
>>
>> I bisected to commit 3298b690b21cdbe6b2ae8076d9147027f396f2b1 ("kbuild: Add
>> a cache for generated variables"). Once I revert this commit, kernel build
>> is fine.
>>
>> gcc 4.8.5 is fine to build kernel with this commit.
>>
>> I'm not quite sure if this is a bug or my gcc install is skewed although it
>> can build kernel without that commit since that commit might exacerbate the
>> case.
>>
>> Any hint is appreciated
>
>
> Today, I was also hit with the same error
> when I was compiling linux-next.
> I am not so sure why this error happens, but
> "make clean" will probably fix the problem.
>
> You need to do "make clean" to blow .cache.mk
> when you upgrade your compiler.
> This is nasty, though...
>


I got it.

The following line in the top-level Makefile.

NOSTDINC_FLAGS += -nostdinc -isystem $(call shell-cached,$(CC)
-print-file-name=include)


If the stale result of -print-file-name is stored in the cache file,
the compiler fails to find <stdarg.h>


-- 
Best Regards
Masahiro Yamada