Re: [PATCH 1/2] x86: Do not add -falign flags unconditionally for clang

Nathan Chancellor
2021-09-16T18:42:36Z

On 9/16/2021 10:18 AM, Borislav Petkov wrote:
> On Mon, Aug 23, 2021 at 07:26:39PM -0700, Nathan Chancellor wrote:
>
> A couple of nitpicks:
>
>> Subject: [PATCH 1/2] x86: Do not add -falign flags unconditionally for clang
>
> Make that prefix into "x86/build: "

Done, I'll be sure to keep that prefix in mind for future flag-based
changes.

>> clang does not support -falign-jumps and only recently gained support
>> for -falign-loops. When one of the configuration options that adds these
>> flags is enabled, clang warns and all cc-{disable-warning,option} that
>> follow fail because -Werror gets added to test for the presence of this
>> warning:
>>
>> clang-14: warning: optimization flag '-falign-jumps=0' is not supported
>> [-Wignored-optimization-argument]
>>
>> To resolve this, add a couple of cc-option calls when building with
>> clang; gcc has supported these options since 3.2 so there is no point in
>> testing for their support. -falign-functions was implemented in clang-7,
>> -falign-loops was implemented in clang-14, and -falign-jumps has not
>> been implemented yet.
>>
>> Link: https://lore.kernel.org/r/YSQE2f5teuvKLkON@Ryzen-9-3900X.localdomain/
>
> Also, there should be a second Link: tag which points to this mail
> thread so that we can find it later, when we dig for the "why we did
> that" question :)
>
> I.e.,
>
> Link: 20210824022640.2170859-2-nathan@kernel.org

Sure thing, kind of hard to do that on the initial submission but I will
do it for the v2 shortly :)

>> Reported-by: kernel test robot <lkp@intel.com>
>> Signed-off-by: Nathan Chancellor <nathan@kernel.org>
>> ---
>> arch/x86/Makefile_32.cpu | 12 +++++++++---
>> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> with that:
>
> Acked-by: Borislav Petkov <bp@suse.de>

Thank you for the ack. The conflicting changes that I mentioned in the
cover letter have been merged in 5.15-rc1 so if you guys want to take
these changes via -tip, just holler for an ack from Masahiro on the
second patch on v2 (but I am going with the assumption this will be
merged via the kbuild tree).

Cheers,
Nathan