linux-kernel - Re: [PATCH v2] m68k: use kernel's generic muldi3 libgcc function

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Message-ID: <1dd8be4b-d5c3-4074-a91e-3ce998ce3050@linux-m68k.org>
Date: Wed, 6 Nov 2024 08:04:44 +1000
From: Greg Ungerer <gerg@...ux-m68k.org>
To: Geert Uytterhoeven <geert@...ux-m68k.org>, arnd@...db.de
Cc: linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] m68k: use kernel's generic muldi3 libgcc function

Hi Geert,

On 5/11/24 21:46, Geert Uytterhoeven wrote:
> Hi Greg, Arnd,
> 
> On Mon, Nov 13, 2023 at 2:32 PM Greg Ungerer <gerg@...ux-m68k.org> wrote:
>> Use the kernels own generic lib/muldi3.c implementation of muldi3 for
>> 68K machines. Some 68K CPUs support 64bit multiplies so move the arch
>> specific umul_ppmm() macro into a header file that is included by
>> lib/muldi3.c. That way it can take advantage of the single instruction
>> when available.
>>
>> There does not appear to be any existing mechanism for the generic
>> lib/muldi3.c code to pick up an external arch definition of umul_ppmm().
>> Create an arch specific libgcc.h that can optionally be included by
>> the system include/linux/libgcc.h to allow for this.
>>
>> Somewhat oddly there is also a similar definition of umul_ppmm() in
>> the non-architecture code in lib/crypto/mpi/longlong.h for a wide range
>> or machines. Its presence ends up complicating the include setup and
>> means not being able to use something like compiler.h instead. Actually
>> there is a few other defines of umul_ppmm() macros spread around in
>> various architectures, but not directly usable for the m68k case.
>>
>> Signed-off-by: Greg Ungerer <gerg@...ux-m68k.org>
> 
> Reviewed-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> 
>>   arch/Kconfig                   |  8 +++
>>   arch/m68k/Kconfig              |  2 +
>>   arch/m68k/include/asm/libgcc.h | 20 +++++++
>>   arch/m68k/lib/Makefile         |  2 +-
>>   arch/m68k/lib/muldi3.c         | 97 ----------------------------------
>>   include/linux/libgcc.h         |  4 ++
>>   6 files changed, 35 insertions(+), 98 deletions(-)
>>   create mode 100644 arch/m68k/include/asm/libgcc.h
>>   delete mode 100644 arch/m68k/lib/muldi3.c
> 
> I had this in my local tree for about a year.
> Is it fine to queue this in the m68k tree, or does this need a broader
> coverage?

I am still in favor of it :-)
Would be good to get some feedback on the common code changes, like the change
to libgcc.h.

Regards
Greg