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@xxxxxxxxxx> 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@xxxxxxxxxxxxxx/ > > [2]https://lore.kernel.org/all/20221216185012.2342675-1-abdulras@xxxxxxxxxx/ Cheers, Conor.
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