Re: [PATCH] kbuild: Use -nostdinc in compile tests

Michal Marek
2014-11-26T13:47:12Z

On 2014-11-25 22:53, Michal Marek wrote:
> Dne 6.11.2014 v 01:58 Ben Hutchings napsal(a):
>> gcc 4.8 and later include <stdc-predef.h> by default. In some
>> versions of eglibc that includes <bits/predefs.h>, but that may be
>> missing when building with a biarch compiler. Also <stdc-predef.h>
>> itself could be missing as we are only trying to build a kernel, not
>> userland.
>>
>> The -nostdinc option disables this, though it isn't explicitly
>> documented. This option is already used when actually building
>> the kernel, but not by cc-option and other tests. This can result
>> in silently miscompiling the kernel.
>>
>> References: https://bugs.debian.org/717557
>> References: https://bugs.debian.org/726861
>> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
>> ---
>> This specific issue appeared and then was fixed in Debian about a year
>> ago, but it seems like it can also affect cross-builds.
>>
>> It may also be worth adding some sort of sanity test, so we stop
>> immediately if $(cc-option $(empty),broken) yields 'broken'.
>>
>> Ben.
>>
>> Makefile | 4 +++-
>> scripts/Kbuild.include | 15 ++++++++-------
>> 2 files changed, 11 insertions(+), 8 deletions(-)
>>
>> diff --git a/Makefile b/Makefile
>> index ffc1ce2..c0fbf67 100644
>> --- a/Makefile
>> +++ b/Makefile
>> @@ -619,6 +619,8 @@ endif
>> # Tell gcc to never replace conditional load with a non-conditional one
>> KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0)
>>
>> +NOSTDINC_FLAGS += -nostdinc
>> +
>> ifdef CONFIG_READABLE_ASM
>> # Disable optimizations that make assembler listings hard to read.
>> # reorder blocks reorders the control in the function
>> @@ -742,7 +744,7 @@ KBUILD_CFLAGS += $(call cc-option, -fno-inline-functions-called-once)
>> endif
>>
>> # arch Makefile may override CC so keep this after arch Makefile is included
>> -NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
>> +NOSTDINC_FLAGS += -isystem $(shell $(CC) -print-file-name=include)
>
> Why not simply move the whole assignment up?

Ah, I see the reason now -- we need $(CC) for the second part of the
assignment.

> Also, there are two
> cc-option tests and one cc-disable-warning test before the first part
> assignment. Looks like a result of a mismerge.

But this still looks like a bug to me.

Michal