Re: gcc10 build issue for Arm64

[Jan Beulich <jbeulich@xxxxxxxx>]

On 27.08.2020 11:11, Julien Grall wrote:
> On 27/08/2020 09:01, Jan Beulich wrote:
>> Stefano, Julien,
> 
> Hi Jan,
> 
>> since it was touching code potentially also affecting Arm, prior
>> to my push of a couple of commits a few minutes ago I also wanted
>> to build-test Arm. While as a fallback all went well with gcc
>> 9.3, with my first (default) attempt with 10.2 I ran into
>>
>> ld: prelink.o: in function `_spin_lock_cb':
>> /build/xen/staging-arm64/xen/common/spinlock.c:164: undefined reference to 
>> `__aarch64_ldadd4_acq_rel'
>> ld: /build/xen/staging-arm64/xen/common/spinlock.c:164: undefined reference 
>> to `__aarch64_ldadd4_acq_rel'
>> make[3]: *** [/build/xen/staging-arm64/xen/xen-syms] Error 1
>> make[2]: *** [/build/xen/staging-arm64/xen/xen] Error 2
>> make[1]: *** [install] Error 2
>> make: *** [install-xen] Error 2
>>
>> I have no idea how recent the introduction of the issue is, but
>> I hope you'll be able to pinpoint the offending change (and a
>> possible fix) much easier than I would be.
> 
> It looks like GCC10 will outline atomic helpers by default. The 
> following hack will do the trick:
> 
> diff --git a/xen/arch/arm/Rules.mk b/xen/arch/arm/Rules.mk
> index e69de29bb2..8dfd9713af 100644
> --- a/xen/arch/arm/Rules.mk
> +++ b/xen/arch/arm/Rules.mk
> @@ -0,0 +1 @@
> +c_flags+=-mno-outline-atomics
> 
> I will clean it up to check it also works with older GCC.

Ah. The option at least is not documented for gcc9. I also think
its (conditional) addition belongs in arch.mk, not Rules.mk,
judging from how it gets done on x86. But I guess sorting this
was meant to be part of your "cleaning it up".

Jan