[PATCH v2] lib: sbi_misaligned_ldst: Add handling of vector load/store

[Anup Patel]

On Mon, Dec 9, 2024 at 10:18 AM Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>
> On 9 Dec 2024, at 03:56, Anup Patel <anup at brainfault.org> wrote:
> >
> > On Mon, Dec 9, 2024 at 1:57 AM Jessica Clarke <jrtc27 at jrtc27.com> wrote:
> >>
> >> On 7 Dec 2024, at 14:31, Anup Patel <apatel at ventanamicro.com> wrote:
> >>>
> >>> On Sat, Dec 7, 2024 at 2:27 AM Clément Léger <cleger at rivosinc.com> wrote:
> >>>>
> >>>> Hi Anup & Nylon,
> >>>>
> >>>> This commits breaks openSBI boot on my setup. A quick analysis of the
> >>>> problem shows that the changes to objects.mk now allows GCC to generate
> >>>> vector assembly in OpenSBI. It now crashes in bitmap_zero() really early
> >>>> (Used in fw_platform_coldboot_harts_init()) due to vector instructions
> >>>> being used:
> >>>>
> >>>>  0x0000000080007800 <+474>:   mv      a0,s2
> >>>>  0x0000000080007802 <+476>:   sw      a5,88(s4)
> >>>>  0x0000000080007806 <+480>:   jal     0x8001adbe <fdt_check_imsic_mlevel>
> >>>> => 0x000000008000780a <+484>:   vsetivli        zero,2,e64,m1,ta,ma
> >>>>  0x000000008000780e <+488>:   vmv.v.i v1,0
> >>>>  0x0000000080007812 <+492>:   mv      a5,a0
> >>>>
> >>>>
> >>>> And then it raises an illegal instruction probably because V isn't
> >>>> enabled. But I'm guessing we do not expect to use vector code in OpenSBI
> >>>> at all ? I'm using a fairly new qemu if that is of any help
> >>>> (248f9209edfd289e7d97fb323e5075ccd55cc157).
> >>>
> >>> Ahh, it seems auto-vectorization is enabled by default.
> >>>
> >>> We certainly don't want to use vector code in OpenSBI
> >>> at the moment.
> >>>
> >>> How about using the compiler command-line option to
> >>> force disable auto-vectorization ?
> >>
> >> Just don’t put V in the ISA string? The assembly already does
> >>
> >>    .option arch, +v
> >>
> >> AFAICT there’s no reason for any C to be compiled with V.
> >
> > This is certainly another way but my worry is compilation would
> > fail for older toolchains without vector support hence my suggestion
> > to disable auto-vectorization.
>
> You still check it’s supported as an option. You just don’t actually
> enable it globally, only on the assembly you need it for.
>

Currently, we depend on the built-in __riscv_vector define which
is available when "v" enabled via "-march".

Now, if we don't enable "v" in "-march" then we will need some
other OpenSBI specific define as well as ".option arch, +v" in
the inline assembly.

Regards,
Anup