[PATCH] powerpc: Add gpr1 and fpu save/restore functions

[Timothy Pearson]

----- Original Message -----
> From: "Segher Boessenkool" <segher at kernel.crashing.org>
> To: "Timothy Pearson" <tpearson at raptorengineering.com>
> Cc: "linuxppc-dev" <linuxppc-dev at lists.ozlabs.org>
> Sent: Monday, February 12, 2024 12:23:22 PM
> Subject: Re: [PATCH] powerpc: Add gpr1 and fpu save/restore functions

> On Mon, Feb 12, 2024 at 12:07:03PM -0600, Timothy Pearson wrote:
>> > I have done it for *all* architectures some ten years ago.  Never found
>> > any problem.
>> 
>> That makes sense, what I mean by invasive is that we'd need buy-in from the
>> other
>> maintainers across all of the affected architectures.  Is that likely to occur?
> 
> I don't know.  Here is my PowerPC-specific patch, it's a bit older, it
> might not apply cleanly anymore, the changes needed should be obvious
> though:
> 
> 
> === 8< ===
> commit f16dfa5257eb14549ce22243fb2b465615085134
> Author: Segher Boessenkool <segher at kernel.crashing.org>
> Date:   Sat May 3 03:48:06 2008 +0200
> 
>    powerpc: Link vmlinux against libgcc.a
> 
> diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
> index b7212b619c52..0a2fac6ffc1c 100644
> --- a/arch/powerpc/Makefile
> +++ b/arch/powerpc/Makefile
> @@ -158,6 +158,9 @@ core-y                              += arch/powerpc/kernel/
> core-$(CONFIG_XMON)            += arch/powerpc/xmon/
> core-$(CONFIG_KVM)             += arch/powerpc/kvm/
> 
> +LIBGCC := $(shell $(CC) $(KBUILD_CFLAGS) -print-libgcc-file-name)
> +libs-y += $(LIBGCC)
> +
> drivers-$(CONFIG_OPROFILE)     += arch/powerpc/oprofile/
> 
> # Default to zImage, override when needed
> === 8< ===

OK.  PowerPC maintainers, how would you prefer to handle this?

>> > There are better options than -Os, fwiw.  Some --param's give smaller
>> > *and* faster kernels.  What exactly is best is heavily arch-dependent
>> > though (as well as dependent on the application code, the kernel code in
>> > this case) :-(
>> 
>> I've been through this a few times, and -Os is the only option that makes
>> things (just barely) fit unfortunately.
> 
> -O2 with appropriate inlining tuning beats -Os every day of the week,
> in my experience.

On 6.6 it's 24MiB vs 40MiB, O2 vs. Os. :(