[PATCH] Trap and Emulate changes

[Anup Patel]

On Thu, Feb 12, 2026 at 8:38 PM Scott Bambrough <scott at riscstar.com> wrote:
>
> Is PMP universally available?

Yes, PMP is not universally available plus we might
not have enough PMP regions.

Cleaner approach is to use an "ecall" based paravirt
interrupt controller.

Regards,
Anup

> Scott
>
> On Thu, Feb 12, 2026 at 9:58 AM Anup Patel <apatel at ventanamicro.com> wrote:
>>
>> On Wed, Feb 11, 2026 at 3:30 PM <dave.patel at riscstar.com> wrote:
>> >
>> > From: Dave Patel <dave.patel at riscstar.com>
>> >
>> > Signed-off-by: Dave Patel <dave.patel at riscstar.com>
>> > ---
>> >  lib/sbi/sbi_illegal_insn.c | 25 ++++++++++++++++++++++++-
>> >  1 file changed, 24 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/lib/sbi/sbi_illegal_insn.c b/lib/sbi/sbi_illegal_insn.c
>> > index fa82264a..88079e39 100644
>> > --- a/lib/sbi/sbi_illegal_insn.c
>> > +++ b/lib/sbi/sbi_illegal_insn.c
>> > @@ -110,10 +110,33 @@ static int system_opcode_insn(ulong insn, struct sbi_trap_regs *regs)
>> >         return 0;
>> >  }
>> >
>> > +static int sbi_get_emulated_irq_insn(ulong insn, struct sbi_trap_regs *regs)
>> > +{
>> > +       ulong rs1_val   = GET_RS1(insn, regs);
>> > +       ulong rs2_val   = GET_RS2(insn, regs);
>> > +       //ulong prev_mode = sbi_mstatus_prev_mode(regs->mstatus);
>> > +       ulong irq_val;
>> > +
>> > +       /*
>> > +       // This is were the emualted irq vlaue is fetched
>> > +       if (prev_mode == PRV_S && sbi_emulate_irq_read(&irq_val))
>> > +               return truly_illegal_insn(insn, regs);
>> > +       */
>> > +
>> > +       // For testing
>> > +       irq_val = rs1_val + rs2_val;
>> > +
>> > +       SET_RD(insn, regs, irq_val);
>> > +
>> > +       regs->mepc += 4;
>> > +
>> > +       return 0;
>> > +}
>> > +
>> >  static const illegal_insn_func illegal_insn_table[32] = {
>> >         truly_illegal_insn, /* 0 */
>> >         truly_illegal_insn, /* 1 */
>> > -       truly_illegal_insn, /* 2 */
>> > +       sbi_get_emulated_irq_insn,   /* 2 */
>>
>> We can't pick arbitrary instruction encoding for
>> trap-n-emulation of an interrupt controller.
>>
>> If the goal is to trap-n-emulate an MMIO device
>> then use PMP based access faults.
>>
>> Regards
>> Anup