Subject: Re: [PATCH v2 1/5] powerpc/kbuild: set default generic machine type for 32-bit compile

From: Segher Boessenkool <[email-masked]>
Date: Thu, 10 May 2018 08:10:03 -0500

On Thu, May 10, 2018 at 03:16:55PM +1000, Nicholas Piggin wrote:
> The 64-bit toolchain uses the wrong ISA variant for compiling 32-bit
> kernels, eve with -m32. Set -mcpu=powerpc which is the generic 32-bit
> powerpc machine type and scheduling model. 32-bit platforms and CPUs
> can override this with -mcpu= options that come later on the command
> line.
> 
> This fixes a lot of build failures due to incompatible assembly when
> compiling 32-bit kernel with 64-bit toolchain.

So what ISA is set for gas without this patch?  With what GCC version?
And, why is that wrong?

Segher

> +ifdef CONFIG_PPC32
> +# These options will be overridden by any -mcpu option that comes
> +# later on the command line, but they are needed to set a sane
> +# 32-bit cpu target for the 64-bit cross compiler.
> +KBUILD_CFLAGS		+= -mcpu=powerpc
> +KBUILD_AFLAGS		+= -mcpu=powerpc
> +endif