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

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Message-ID: <7bb57485-c08c-4121-ade5-8c76bc48e615@linux-m68k.org>
Date: Mon, 2 Dec 2024 11:34:11 +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

Arnd, ping...


On 6/11/24 08:04, Greg Ungerer wrote:
> 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
> 
> 
View attachment "0001-m68k-use-kernel-s-generic-muldi3-libgcc-function.patch" of type "text/x-patch" (7339 bytes)