Bug#996419: gcc-11: Fails to compile the linux kernel on ARM

[Matthias Klose <doko@debian.org>]

On 10/18/21 9:03 AM, Sebastian Andrzej Siewior wrote:
> On 2021-10-16 12:17:40 [+0200], Matthias Klose wrote:
>> The change is intended; the configure changes are already in GCC 8, but the
>> configure options that we used, are now being deprecated upstream.
>>
>> Changes: https://gcc.gnu.org/gcc-8/changes.html
> 
> I guess you refer to
> | The -march and -mcpu options now accept optional extensions…
> 
> which describes the syntax. But this is gcc-8 introducing new syntax not
> gcc-11 dropping old syntax or so.
> 
>>> On gcc-10 it evaluated to "-march=armv7-a".
>>> On gcc-11 it evaluates to "-march=armv5t -Wa,-march=armv7-a" leading to
>>
>> -march=armv7-a+fp probably should be used. Same in assembler files where armv7-a
>> is used as an architecture. I'm not a kernel developer however, so don't know if
>> this is the intended approach.
> 
> I was asking because `gcc -v' changes from
>   --with-arch=armv7-a --with-fpu=vfpv3-d16
> to
>   --with-arch=armv7-a+fp
> 
> and I wasn't sure if this is intended or a side effect. But it may be
> mandatory due to the new syntax.

CCing Richard. I've been told that the --with-fpu configure option is deprecated
now, therefore changing the way this is configured.

> As for the option, I would guess "armv7-a+nofp" since the expectation is
> not to clobber any FPU/SIMD registers like in auto-vectorization etc.
> But I see Arnd is on Cc: and silently hope he looks into it ;)

I also backported
"ARM: pass architecture extensions to assembler if supported." from the trunk,
applied in the gcc-11 Debian package.
https://gcc.gnu.org/pipermail/gcc-patches/2021-September/579897.html

Matthias