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

[Anup Patel]

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.

Regards,
Anup