Messages in this thread | | | Date | Wed, 08 Feb 2023 09:56:06 -0800 (PST) | Subject | Re: [PATCH] riscv: avoid enabling vectorized code generation | From | Palmer Dabbelt <> |
| |
On Fri, 16 Dec 2022 10:50:12 PST (-0800), abdulras@google.com wrote: > The compiler is free to generate vectorized operations for zero'ing > memory. The kernel does not use the vector unit on RISCV, similar to > architectures such as x86 where we use `-mno-mmx` et al to prevent the > implicit vectorization. Perform a similar check for > `-mno-implicit-float` to avoid this on RISC-V targets. > > Signed-off-by: Saleem Abdulrasool <abdulras@google.com> > --- > arch/riscv/Makefile | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile > index 0d13b597cb55..68433476a96e 100644 > --- a/arch/riscv/Makefile > +++ b/arch/riscv/Makefile > @@ -89,6 +89,10 @@ KBUILD_AFLAGS_MODULE += $(call as-option,-Wa$(comma)-mno-relax) > # architectures. It's faster to have GCC emit only aligned accesses. > KBUILD_CFLAGS += $(call cc-option,-mstrict-align) > > +# Ensure that we do not vectorize the kernel code when the `v` extension is > +# enabled. This mirrors the `-mno-mmx` et al on x86. > +KBUILD_CFLAGS += $(call cc-option,-mno-implicit-float) > + > ifeq ($(CONFIG_STACKPROTECTOR_PER_TASK),y) > prepare: stack_protector_prepare > stack_protector_prepare: prepare0
Sorry to just restart the thread, but there's been discussions on this in a bunch of places. From my understanding, we don't actually need this: we have this tricky line in the Makefile
KBUILD_CFLAGS += -march=$(subst fd,,$(riscv-march-y))
that removes the floating-point extenions from what the kernel is built with, so adding `-mno-implicit-float` doesn't actually do anything (and we'd end up with essentially the same thing for V when it gets added).
So unless I'm missing something, we don't need this.
| |