Re: [PATCH -next v13 19/19] riscv: Enable Vector code to be built

Conor Dooley
2023-02-08T18:19:24Z

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Hey Andy,

On Mon, Jan 30, 2023 at 08:13:20AM +0000, Conor Dooley wrote:
> On Mon, Jan 30, 2023 at 03:46:32PM +0800, Andy Chiu wrote:
> > On Thu, Jan 26, 2023 at 5:04 AM Conor Dooley <conor@kernel.org> wrote:
> > > Firstly, no-implicit-float is a CFLAG, so why add it to march?
> > I placed it in march because I thought we need the flag in vdso. And,
> > KBUILD_CFLAGS is not enough for vdso. However, I think we don't need
> > this flag in vdso since it is run in user space anyway.
> > > There is an existing patch on the list for enabling this flag, but I
> > > recall Palmer saying that it was not actually needed?
> > The flag is needed for clang builds to prevent auto-vectorization from
> > using V in the kernel code [1].
> >
> > > Palmer, do you remember why that was?
> > The discussion[2] suggested that we need this flag, IIUC. But somehow
> > the patch did make it into the tree.
>
> I know, in [1] I left an R-b as the patch seemed reasonable to me.
> Palmer mentioned some reason for not thinking it was actually needed but
> not on-list, so I was hoping he'd comment!

Palmer replied there today with his rationale & an expectation that we
do the same thing for vector as we did for float:
https://lore.kernel.org/linux-riscv/mhng-4c71ada6-003c-414f-9a74-efa3ccd2856b@palmer-ri-x1c9/T/#m366779709bbcf7672b5277b3bb27a7d6ce6c6115

>
> And I suppose, it never got any further attention as it isn't needed by
> any in-tree code?
>
> > [1]https://lore.kernel.org/all/CAOnJCULtT-y9vo6YhW7bW9XyKRdod-hvFfr02jHVamR_LcsKdA@mail.gmail.com/
> > [2]https://lore.kernel.org/all/20221216185012.2342675-1-abdulras@google.com/

Cheers,
Conor.

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