SSE instructions

[Simon Glass]

Hi Heinrich,

On Thu, 28 Sept 2023 at 00:26, Heinrich Schuchardt
<heinrich.schuchardt at canonical.com> wrote:
>
> On 9/28/23 04:41, Simon Glass wrote:
> > Hi Bin,
> >
> > U-Boot 64-bit on x86 disables sse, but when enabling Truetype I get a
> > compiler error:
> >
> > drivers/video/console_truetype.c: In function 'frac':
> > drivers/video/console_truetype.c:30:15: error: SSE register return
> > with SSE disabled
> > 30 | static double frac(double val)
> >
> > Do you know how to enable SSE for 64-bit?
>
> How could this occur if x86 disables SSE? There must be some
> inconsistency in how this module is built.

We disable SSE on 64-bit x86, even though the CPU always supports it.
The compiler assumes it is available, so presumably emits SSE things.

I suspect there is some CPU init missing after U-Boot changes to
64-bit long mode.

>
> We a need a clarification of the used ABI per architecture and write
> this into our documentation.
>
> The RISC-V profile specification does not foresee float and double in
> S-mode (see RVA20S64 and RVAS22S64 profiles in
> https://github.com/riscv/riscv-profiles/blob/main/profiles.adoc#52-rva20s64-profile).
>
> We should convert drivers/video/console_truetype.c to use integers
> (where low bits are used for the fractional part) instead of float and
> double to make the driver compatible to non-x86 platforms.

Good luck with that :-) It uses STB for Truetype...probably there is
an integer implementation somewhere but I'm not sure.

Regards,
Simon