Re: gcc10 build issue for Arm64

[Julien Grall <julien@xxxxxxx>]

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.

Cheers,

--
Julien Grall