Re: [PATCH] target/riscv: add zicsr/zifencei to isa_string

[Hongren (Zenithal) Zheng]

On Mon, May 23, 2022 at 09:22:15AM +1000, Alistair Francis wrote:
> On Wed, May 18, 2022 at 10:50 PM Hongren (Zenithal) Zheng <i@zenithal.me> 
> wrote:
> >
> > Zicsr/Zifencei is not in 'I' since ISA version 20190608,
> > thus to fully express the capability of the CPU,
> > they should be exposed in isa_string.
> >
> > Signed-off-by: Hongren (Zenithal) Zheng <i@zenithal.me>
> > ---
> >  target/riscv/cpu.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/target/riscv/cpu.c b/target/riscv/cpu.c
> > index 6d01569cad..61fa9b97a4 100644
> > --- a/target/riscv/cpu.c
> > +++ b/target/riscv/cpu.c
> > @@ -1027,6 +1027,8 @@ static void riscv_isa_string_ext(RISCVCPU *cpu, char 
> > **isa_str, int max_str_len)
> >       *    extensions by an underscore.
> >       */
> >      struct isa_ext_data isa_edata_arr[] = {
> > +        ISA_EDATA_ENTRY(zicsr, ext_icsr),
> > +        ISA_EDATA_ENTRY(zifencei, ext_ifencei),
> 
> Shouldn't we have a spec version check here?

I think that can be done, but most of the time it is not necessary.
For old specs, the "short-isa-string" can be a workaround.

This patch is actually a follow-up of "target/riscv: Change "G" expansion"
https://github.com/alistair23/qemu/commit/72bd25b7b88d0536bfb5666990e296587d4057a5
where "G" is expanded with "zicsr"/"zifencei" without checking
unpriv spec version.

>From the summary from Kito from gnu toolchain
https://lkml.org/lkml/2022/1/24/537
we know that there are at least 3 formally released unpriv specs:
2.2, 20190608 and 20191213, and frequent informal release from
https://github.com/riscv/riscv-isa-manual/releases

If we add a spec check, we need to add a PROP_STRING and
and parse the version. We then need an enum like
PRIV_VERSION_1_12_0 and we needs to g_strcmp0
in riscv_cpu_realize, just as what priv spec had done.

And we need to define a default unpriv spec version, which
should be 20191213.

I can add a separate patch for it if you do think it is necessary.

If the guest does want old spec version, I think the recently added
"short-isa-string" option from Tsukasa OI is suitable.
Instead of -cpu rv64,unpriv_spec=2.2 they can just use
-cpu rv64,short-isa-string=true to solve the issue.

Cc Tsukasa OI

> 
> Alistair
> 
> >          ISA_EDATA_ENTRY(zfh, ext_zfh),
> >          ISA_EDATA_ENTRY(zfhmin, ext_zfhmin),
> >          ISA_EDATA_ENTRY(zfinx, ext_zfinx),
> > --
> > 2.35.1
> >
> >