Hi, Palmer,
On Fri, Jan 12, 2024 at 10:03 PM Palmer Dabbelt <pal...@rivosinc.com> wrote:
>
> On Fri, 12 Jan 2024 12:57:22 PST (-0800), r...@rivosinc.com wrote:
> > Commit f4e1168198 (linux-user: Split out host_sig{segv,bus}_handler)
> > introduced a bug, when returning from host_sigbus_handler the PC is
>
> So we should probably have a
>
> Fixes: f4e1168198 ("linux-user: Split out host_sig{segv,bus}_handler")
You are correct.
>
> > never set. Thus cpu_loop_exit_restore is called with a zero PC and
> > we immediate get a SIGSEGV.
> >
> > Signed-off-by: Robbin Ehn <r...@rivosinc.com>
> > ---
> > linux-user/signal.c | 5 +++--
> > 1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/linux-user/signal.c b/linux-user/signal.c
> > index b35d1e512f..c9527adfa3 100644
> > --- a/linux-user/signal.c
> > +++ b/linux-user/signal.c
> > @@ -925,7 +925,7 @@ static void host_sigsegv_handler(CPUState *cpu,
> > siginfo_t *info,
> > cpu_loop_exit_sigsegv(cpu, guest_addr, access_type, maperr, pc);
> > }
> >
> > -static void host_sigbus_handler(CPUState *cpu, siginfo_t *info,
> > +static uintptr_t host_sigbus_handler(CPUState *cpu, siginfo_t *info,
> > host_sigcontext *uc)
> > {
> > uintptr_t pc = host_signal_pc(uc);
> > @@ -947,6 +947,7 @@ static void host_sigbus_handler(CPUState *cpu,
> > siginfo_t *info,
> > sigprocmask(SIG_SETMASK, host_signal_mask(uc), NULL);
> > cpu_loop_exit_sigbus(cpu, guest_addr, access_type, pc);
> > }
> > + return pc;
> > }
> >
> > static void host_signal_handler(int host_sig, siginfo_t *info, void *puc)
> > @@ -974,7 +975,7 @@ static void host_signal_handler(int host_sig, siginfo_t
> > *info, void *puc)
> > host_sigsegv_handler(cpu, info, uc);
>
> Do we have the same problem for SEGV? They both used to set
Yea, it's not easy to follow the different paths... this code needs
another refactor, I was tempted but refrained myself.
So in the switch state if we have SEGV (and si_code>0) we always long
jump or return.
Only SIGBUS sets sync_sig to true, and thus calls
cpu_loop_exit_restore, hence needs a PC.
But the comment makes you think it's for multiple signals.
>
> pc = host_signal_pc(uc);
>
> but with this it's only SIGBUS. Maybe the same for the others, so just
> something like
>
> diff --git a/linux-user/signal.c b/linux-user/signal.c
> index b35d1e512f..55840bdf31 100644
> --- a/linux-user/signal.c
> +++ b/linux-user/signal.c
> @@ -968,6 +968,8 @@ static void host_signal_handler(int host_sig,
> siginfo_t *info, void *puc)
> * SIGFPE, SIGTRAP are always host bugs.
> */
> if (info->si_code > 0) {
> + pc = host_signal_pc(uc);
> +
> switch (host_sig) {
> case SIGSEGV:
> /* Only returns on handle_sigsegv_accerr_write success. */
>
Only those (SIGBUS) setting sync_sig need a PC.
> as it just does the PC chasing for everyone?
>
The sneaky return below.
Let me know if you still think setting the PC before the switch
statement is better.
> > return;
> > case SIGBUS:
> > - host_sigbus_handler(cpu, info, uc);
> > + pc = host_sigbus_handler(cpu, info, uc);
> > sync_sig = true;
> > break;
> > case SIGILL:
> > --
> > 2.40.1
>
> Either way,
>
> Reviewed-by: Palmer Dabbelt <pal...@rivosinc.com>
Thanks!
>
> Thanks!
