Re: [PATCH] target/riscv: set tval for triggered watchpoints

[Sergey Matyukevich]

Hi Bin,

> > > According to priviledged spec, if [sm]tval is written with a nonzero
> > > value when a breakpoint exception occurs, then [sm]tval will contain
> > > the faulting virtual address. Set tval to hit address when breakpoint
> > > exception is triggered by hardware watchpoint.
> > >
> > > Signed-off-by: Sergey Matyukevich <sergey.matyukev...@syntacore.com>
> >
> > Thanks!
> >
> > Applied to riscv-to-apply.next
> 
> Oops, too quick, but I have one comment :)
> 
> >
> > Alistair
> >
> > > ---
> > >  target/riscv/cpu_helper.c | 3 +++
> > >  target/riscv/debug.c      | 1 +
> > >  2 files changed, 4 insertions(+)
> > >
> > > diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
> > > index 9a28816521..d3be8c0511 100644
> > > --- a/target/riscv/cpu_helper.c
> > > +++ b/target/riscv/cpu_helper.c
> > > @@ -1641,6 +1641,9 @@ void riscv_cpu_do_interrupt(CPUState *cs)
> > >          case RISCV_EXCP_VIRT_INSTRUCTION_FAULT:
> > >              tval = env->bins;
> > >              break;
> > > +        case RISCV_EXCP_BREAKPOINT:
> > > +            tval = env->badaddr;
> 
> RISCV_EXCP_BREAKPOINT may come from 'ebreak' so we should test if this
> exception comes from the debug module.
> 
> The spec also says about icount trigger that:
> 
> "If the trigger fires with action =0 then zero is written to the tval
> CSR on the breakpoint trap."
> 
> So we can't blindly set tval for every breakpoint exception.
> 

Thanks for catching ! Initial idea was to set badaddr value only when
it is needed in target/riscv/debug.c. For instance, icount code does
not set badaddr, so tval will remain zero. On the other hand, breakpoint
exception may come from ebreak and badaddr may keep non-zero value from
some previous unrelated exception.

Explicit check should be more safe, e.g. something like that:

diff --git a/target/riscv/cpu_helper.c b/target/riscv/cpu_helper.c
index d3be8c0511..f1a0c65ad3 100644
--- a/target/riscv/cpu_helper.c
+++ b/target/riscv/cpu_helper.c
@@ -1642,7 +1642,10 @@ void riscv_cpu_do_interrupt(CPUState *cs)
             tval = env->bins;
             break;
         case RISCV_EXCP_BREAKPOINT:
-            tval = env->badaddr;
+            if (cs->watchpoint_hit) {
+                tval = cs->watchpoint_hit->hitaddr;
+                cs->watchpoint_hit = NULL;
+            }
             break;
         default:
             break;
diff --git a/target/riscv/debug.c b/target/riscv/debug.c
index 48ef3c59ea..b091293069 100644
--- a/target/riscv/debug.c
+++ b/target/riscv/debug.c
@@ -761,8 +761,6 @@ void riscv_cpu_debug_excp_handler(CPUState *cs)
 
     if (cs->watchpoint_hit) {
         if (cs->watchpoint_hit->flags & BP_CPU) {
-            env->badaddr = cs->watchpoint_hit->hitaddr;
-            cs->watchpoint_hit = NULL;
             do_trigger_action(env, DBG_ACTION_BP);
         }
     } else {


I will a fixup after testing.

Regards,
Sergey