Problems building ppc images in v4.14.y and v4.16.y using gcc 7.3.0 / 8.1.0 from kernel.org

[Arnd Bergmann]

On Tue, Jun 5, 2018 at 3:52 PM, Guenter Roeck <linux at roeck-us.net> wrote:
> Hi Arnd,
>
> when using the ppc64 compiler from kernel.org, I see the following problems
> when trying to compile ppc:allnoconfig in v4.14.y or v4.16.y.
>
> gcc 7.3.0: Compilation of kernel.cpu.o hangs
>
> The problem goes away if I apply the following two patches (tested with
> 4.16.y)
>
> 17a2f1ced028 cpu/hotplug: Merge cpuhp_bp_states and cpuhp_ap_states
> fcb3029a8d89 cpu/hotplug: Fix unused function warning

This is probably the same as
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84038

I thought I had included the fix in my builds.

> gcc 8.1.0: Compilation of kernel/cpu.o results in the following error
>
> powerpc64-linux-gcc: error: unrecognized command line option '-mno-spe'; did
> you mean '-fno-see'?
> powerpc64-linux-gcc: error: unrecognized command line option '-mspe=no'; did
> you mean '-misel=no'?
>
> This problem is also seen with mainline.

I've seen it, but couldn't figure out what the right fix is. I ended
up commenting
out those two lines in my private builds:

--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -215,8 +215,8 @@ KBUILD_CFLAGS += $(call cc-option,-mno-vsx)

 # No SPE instruction when building kernel
 # (We use all available options to help semi-broken compilers)
-KBUILD_CFLAGS += $(call cc-option,-mno-spe)
-KBUILD_CFLAGS += $(call cc-option,-mspe=no)
+#KBUILD_CFLAGS += $(call cc-option,-mno-spe)
+#KBUILD_CFLAGS += $(call cc-option,-mspe=no)

 # Enable unit-at-a-time mode when possible. It shrinks the
 # kernel considerably.

I think there were some changes in how cc-option gets evaluated, maybe
those rely on something else to be enabled or disabled first?

        Arnd