[OE-core] [PATCH 01/12] tune/arm: Set -mtune instead of -mcpu

[Andre McCurdy]

On Wed, Jun 6, 2018 at 10:58 PM, Khem Raj <raj.khem at gmail.com> wrote:
> On 6/6/18 4:42 PM, Andre McCurdy wrote:
>> On Wed, Jun 6, 2018 at 3:43 PM, Khem Raj <raj.khem at gmail.com> wrote:
>>
>> The -mcpu, -march and -mtune options are not new and gcc 6 and 7 catch
>> the same conflicts. It doesn't make sense that gcc8 is just catching
>> more issues.
>
> It does make sense. the option parsing for these specific options on arm
> have been revamped after gcc7, see
>
> https://github.com/kraj/gcc/compare/a99ae290af49793cd3db7a74f3dbc59e64d356a1...68b54adbd7b10c66d968d74b96fba552bd46ebb7

Thanks. These commits seem to be related to handling of options like
"-mcpu=cortexa9+nosimd". Was that the error you saw in testing?

If you can provide the command line that caused the error then it
should be quick to establish whether it's gcc8 being more picky.

Or perhaps there's always been a warning and -Werror has been added to
a gcc8 Makefile where it wasn't before?

>> If we are trying to build something which is reusable across multiple
>> machines with the same architecture then it's a bug to be passing
>> machine specific CFLAGS. Making the machine specific CFLAGS more
>> generic is not the right solution.
>
> being reusable is a side-effect and a good one. Real problem is we are not
> matching to what we say in package arches, Probably you are confusing tunes
> to be meant for static code generation for a given CPU.

Sorry, I don't really follow what you mean?

> I am interested to
> hear more ideas to what would be right solution if this is not it.

I'd like to understand what the problem is first before trying to
propose any solutions.

ie what specifically has changed with gcc8 to cause the error which
wasn't seen before?

>> Anyway, I suspect the real issue here is that when we build gcc to run
>> on the target we currently configure using "--with-arch=armv7-a" for
>> both armv7a and armv7ve. It was done that way deliberately to try to
>> avoid rebuilds when switching between armv7a and armv7ve machines,
>> although thinking about that now I'm not sure it makes so much sense.
>> Does your original problem go away if you simply change:
>>
>>    EXTRA_OECONF_append_armv7ve = " --with-arch=armv7-a"
>>
>> to
>>
>>    EXTRA_OECONF_append_armv7ve = " --with-arch=armv7ve"
>>
>> in gcc-target.inc ?
>
> No, this is not the problem I am talking about gcc-runtime which is
> configured during cross build but built for target later on.

OK, good to rule that out. It's nothing to do with gcc8 and I've sent
a separate patch to fix it.