Re: [PATCH 1/5] target/riscv: Ignore the S and U letters when formatting ISA strings

[Alistair Francis]

On Sat, Aug 6, 2022 at 2:08 AM Conor Dooley <mail@conchuod.ie> wrote:
>
> From: Palmer Dabbelt <palmer@sifive.com>
>
> The ISA strings we're providing from QEMU aren't actually legal RISC-V
> ISA strings, as both S and U cannot exist as single-letter extensions
> and must instead be multi-letter strings.  We're still using the ISA
> strings inside QEMU to track the availiable extensions, so just strip
> out the S and U extensions when formatting ISA strings.
>
> Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
> [Conor: rebased on 7.1.0-rc1 & slightly tweaked the commit message]
> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
> ---
>  target/riscv/cpu.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> index ac6f82ebd0..95fdc03b3d 100644
> --- a/target/riscv/cpu.c
> +++ b/target/riscv/cpu.c
> @@ -1122,7 +1122,23 @@ char *riscv_isa_string(RISCVCPU *cpu)
>      char *p = isa_str + snprintf(isa_str, maxlen, "rv%d", TARGET_LONG_BITS);
>      for (i = 0; i < sizeof(riscv_single_letter_exts) - 1; i++) {
>          if (cpu->env.misa_ext & RV(riscv_single_letter_exts[i])) {
> -            *p++ = qemu_tolower(riscv_single_letter_exts[i]);

riscv_single_letter_exts doesn't contain S or U, is this patch still required?

Alistair

> +            char lower = qemu_tolower(riscv_single_letter_exts[i]);
> +            switch (lower) {
> +                case 's':
> +                case 'u':
> +                    /*
> +                    * The 's' and 'u' letters shouldn't show up in ISA 
> strings as
> +                    * they're not extensions, but they should show up in 
> MISA.
> +                    * Since we use these letters interally as a pseudo ISA 
> string
> +                    * to set MISA it's easier to just strip them out when
> +                    * formatting the ISA string.
> +                    */
> +                    break;
> +
> +                default:
> +                    *p++ = lower;
> +                    break;
> +            }
>          }
>      }
>      *p = '\0';
> --
> 2.37.1
>
>