Re: [PATCH v2 1/3] powerpc: sstep: Fix load and update emulation

Hi!

I didn't see this until now, almost a month later, sorry about that :-)

On Thu, Feb 04, 2021 at 01:57:53PM +0530, Naveen N. Rao wrote:

On 2021/02/03 03:17PM, Segher Boessenkool wrote:

quoted

Power8 does:

  Load with Update Instructions (RA = 0)
    EA is placed into R0.
  Load with Update Instructions (RA = RT)
    EA is placed into RT. The storage operand addressed by EA is
    accessed, but the data returned by the load is discarded.

I'm actually not seeing that. This is what I am testing with:
	li      8,0xaaa
	mr      6,1
	std     8,64(6)
	#ldu    6,64(6)
	.long	0xe8c60041

And, r6 always ends up with 0xaea. It changes with the value I put into 
r6 though.

That is exactly the behaviour specified for p8.  0aaa+0040=0aea.

Granted, this is all up in the air, but it does look like there is more 
going on and the value isn't the EA or the value at the address.

That *is* the EA.  The EA is the address the insn does the access at.


Segher