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

[Jessica Clarke]

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.

Jess