On 2021/03/01 08:37PM, Segher Boessenkool wrote: > Hi! > > I didn't see this until now, almost a month later, sorry about that :-)
No problem. > > On Thu, Feb 04, 2021 at 01:57:53PM +0530, Naveen N. Rao wrote: > > On 2021/02/03 03:17PM, Segher Boessenkool wrote: > > > 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. I'm probably missing something here. 0xaaa is the value I stored at an offset of 64 bytes from the stack pointer (r1 is copied into r6). In the ldu instruction above, the EA is 64(r6), which should translate to r1+64. The data returned by the load would be 0xaaa, which should be discarded per the description you provided above. So, I would expect to see a 0xc0.. address in r6. In fact, this looks to be the behavior documented for P9: > > Power9 does: > > > > Load with Update Instructions (RA = 0) > > EA is placed into R0. > > Load with Update Instructions (RA = RT) > > The storage operand addressed by EA is accessed. The > > displacement > > field is added to the data returned by the load and placed into > > RT. - Naveen
