Re: [Qemu-devel] [PATCH 11/11] target/hppa: call eval_interrupt() after ssm

[Sven Schnelle]

Hi Richard,

On Mon, Mar 11, 2019 at 09:01:32PM -0700, Richard Henderson wrote:
> On 3/11/19 8:28 PM, Richard Henderson wrote:
> > On 3/11/19 12:16 PM, Sven Schnelle wrote:
> >> HP-UX (all versions) is losing timer interrupts, which leads to
> >> hangs. Pressing a key on the console fixes this, so it looks like
> >> QEMU is just looping trough TBs without checking for interrupts.
> >> Further investion showed that this happens when interrupts are
> >> triggered, without PSW_I enabled. Calling eval_interrupt() after
> >> PSW_I is set seems to fix this.
> >>
> >> Signed-off-by: Sven Schnelle <address@hidden>
> >> ---
> >>  target/hppa/cpu.h        | 1 +
> >>  target/hppa/int_helper.c | 2 +-
> >>  target/hppa/op_helper.c  | 6 ++++++
> >>  3 files changed, 8 insertions(+), 1 deletion(-)
> > 
> > The correct fix is to exit to the main loop.
> 
> ... except what we're already doing that.  So I don't see what
> can be changed to help.  This doesn't seem to make a difference.

I looked into this again, and with my limited TCG knowledge it looks like the
exit_tb is not happening because ssm is called in a branch delay slot:

This is the TB it's calling when it looses the timer interrupt:

IN: 
0x0000000000045758:  bv r0(rp)
0x000000000004575c:  ssm 1,r0

OP:
 ld_i32 tmp0,env,$0xffffffffffffffe0
 movi_i32 tmp1,$0x0
 brcond_i32 tmp0,tmp1,lt,$L0

 ---- 0000000000045758 000000000004575c
 mov_i32 tmp0,r2
 mov_i32 iaoq_b,tmp0

 ---- 000000000004575c 00000000ffffffff
 movi_i32 tmp1,$0x4
 add_i32 tmp0,iaoq_b,tmp1
 ld_i32 tmp1,env,$0x1c0
 movi_i32 tmp2,$0x1
 or_i32 tmp1,tmp1,tmp2
 call swap_system_mask,$0x1,$1,tmp1,env,tmp1

Everything above is ssm, and below this is the branch instruction, which skips
the exit_tb (i think):

 mov_i32 iaoq_f,iaoq_b
 mov_i32 iaoq_b,tmp0
 mov_i64 iasq_f,iasq_b
 call lookup_tb_ptr,$0x6,$1,tmp3,env
 goto_ptr tmp3
 set_label $L0
 exit_tb $0x7f373c33cb83

I might also be totally wrong, let me know if that's the case. ;-)

Regards
Sven