Re: ppc64 XER potentially ignored/not setting

[Kyle Lehman]

On 11/16/21 02:26, Thomas Huth wrote:

> > Upon execution r3 is set correctly to 0xffffffffff823456, however ca 
> > is not set within the XER when it should be.
>
> Could you reproduce the issue with a stand alone binary, too? ... it 
> would be interesting to know whether the problem is in the GDB interface 
> or in the emulation part...
>
>   Thomas

Upon further review, turns out this is mostly user error on my part.

When I built the latest qemu, I started immediately manually debugging 
it with standard human readable GDB to see if it solved the issue.  So I 
did my steps in the test, looked at register 'xer' and noticed it still 
sat at 0.  Which where my original post comes from.

In the mean time, I then moved to implement more features with my 
automated testing which uses the machine interface format of GDB.  There 
I noticed register x 69 (XER) was indeed being modified.  Great!

This was confusing, but at least I narrowed something down.  This was 
until I was back into manual GDB side of things, did a register dump and 
noticed 'xer' was listed there twice.  One had 0, the other held a value.

So, in short, I was looking at the duplicated xer set to 0 instead of 
the "real" one within GDB.  Embarrassing to say the least that I didn't 
notice it sooner, but in my defense the old noggin sometimes gets into a 
haze staring at these things.

Emulation side of things appears fine, I ran our test cases that put XER 
through its paces and the results tie out perfectly.

To recap:
1) XER emulation fine (for our test cases)
2) Register setting/getting from x 69 using GDB MI works fine
3) xer shows up twice in normal GDB mode, with one that appears attached 
to nothing.  Setting xer in this mode (set $xer=whatever) does in fact 
get picked up properly within emulation

Thank you for all the effort.  Definitely not an easy ISA to emulate and 
can make your head spin sometimes.

Kyle