On 2/14/24 19:35, Charlie Jenkins wrote:
On Wed, Feb 14, 2024 at 10:00:37PM -0500, John David Anglin wrote:
On 2024-02-14 8:58 p.m., Guenter Roeck wrote:
Specifically: Yes, the carry/borrow bits should be restored. Question is
if the Linux kernel's interrupt handler doesn't restore the carry bits
or if the problem is on the qemu side.
The carry/borrow bits in the PSW should be saved and restored by the save_specials
and rest_specials macros. They are defined in arch/parisc/include/asm/assembly.h.
Why would they be needed to be restored in linux? The manual says "The
PSW is set to the contents of the IPSW by the RETURN FROM INTERRUPTION
instruction". This means that the PSW must be restored by the hardware.
We can see the QEMU implementation in:
rfi:
https://github.com/qemu/qemu/blob/v8.2.1/target/hppa/sys_helper.c#L93
handling interrupt:
https://github.com/qemu/qemu/blob/v8.2.1/target/hppa/int_helper.c#L109
However the implementation appears to be faulty. During an RFI, the PSW
is always set to 0x804000e (regardless of what the PSW was before the
interrupt).
Not sure if I agree. The interrupt handler in Linux is the one which needs to set
IPSW. Looking into the code, I agree with Dave that the tophys macro seems to
clobber the carry bits before psw is saved, so they can not really be restored.
The only issue with that idea is that I can only reproduce the problem with
an interrupted ldd instruction but not, for example, with ldw. This is why it
would be really important to have someone with real hardware test this.
Thanks,
Guenter
