Re: [PATCH] RISC-V: Initialize the jvt CSR

[Kito Cheng <kito.cheng@gmail.com>]

On Fri, Jan 5, 2024 at 11:07 AM Hau Hsu <hau.hsu@sifive.com> wrote:
>
> Set symbol '__jvt_base$' as weak. So if the symbol is not set in the
> linker script, the address would be 0. We initialize jvt CSR only if
> the address is not 0.
>
> Also use csr number directly instead of using symbolic name to prevent the
> backward incompatible issue.
>
> psabi reference:
> https://github.com/riscv-non-isa/riscv-elf-psabi-doc/blob/2d770815dc9a8b11e61ea1abd487cb25ee56ad5e/riscv-elf.adoc#table-jump-relaxation
> ---
>  libgloss/riscv/crt0.S | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
>
> diff --git a/libgloss/riscv/crt0.S b/libgloss/riscv/crt0.S
> index 7a4e4e32c..187ca4a56 100644
> --- a/libgloss/riscv/crt0.S
> +++ b/libgloss/riscv/crt0.S
> @@ -26,6 +26,19 @@ _start:
>    addi  gp, gp, %pcrel_lo(1b)
>  .option pop
>
> +  /* Initialize jvt CSR (reg addr: 0x0017) */
> +  .weak __jvt_base$
> +  lla a0, __jvt_base$
> +  beqz a0, .Ljvt_init_end
> +  /* Enable zicsr to set jvt.
> +     Also need to exclude conflict extensions.  */

^^^ comment seems not in sync with the code?

> +.option push
> +.option norelax
> +.option arch, +zicsr
> +  csrw 0x17, a0
> +.option pop
> +.Ljvt_init_end:
> +
>    # Clear the bss segment
>    la      a0, __bss_start
>    la      a2, _end
> --
> 2.37.1
>