Messages in this thread | | | Date | Fri, 10 May 2024 23:26:22 +0100 | From | Conor Dooley <> | Subject | Re: [PATCH v2 2/8] riscv: Add PLATFORM_MAY_SUPPORT_RISCV_ISA_V Kconfig option |
| |
On Fri, May 10, 2024 at 02:43:10PM -0700, Charlie Jenkins wrote: > On Fri, May 10, 2024 at 09:43:33PM +0100, Conor Dooley wrote: > > Hey Charlie, > > > > On Tue, May 07, 2024 at 06:36:28PM -0700, Charlie Jenkins wrote: > > > Current versions of the kernel add "v" to the march and then immeidately > > > filter it out such that "v" is not passed to CFLAGS. Instead of doing > > > this filtering, code blocks in the kernel that want to use vector > > > assembly have been changed to locally enable vector (using ".option > > > arch, +v"). > > > > Other content in the series aside, since this is a change that could be > > made independently of the main series objectives, I figured it was worth > > pointing out that this is not a change without downsides: I think that > > it would drop support for vector with most versions of LLVM as > > .option arch support there is much more recent thing than it is for gcc. > > Off the top of my head I don't know exactly the versions involved, but > > it is something like LLVM-14 supports vector but only LLVM-17 and later > > supports .option arch. > > Toolchain incompatibilities are always fun. It does look like .option > arch was introduced in LLVM-17. That would be a regression. We do use > .option arch for every other extension, but vector was treated special > when it was introduced unfortunately so maybe we have to live with the > weird march parsing hack.
I wrote out a long message about the history of some of this, but right at the end I was scrolling through my chat logs with Andy and realised we actually did make it depend on AS_HAS_OPTION_ARCH, so it should be safe to do without regressing anything. I didn't notice in the diff that the AS_HAS_OPTION_ARCH was a movement, not an addition. Maybe Andy knows why, despite the dependency on the assembler having it, we didn't use it everywhere.
[unhandled content-type:application/pgp-signature] | |