On 5/9/24 00:24, Thiago Jung Bauermann wrote:
>> One last point, doesn't record/replay require single-stepping each instruction
>> individually? Does that go against the atomic block approach?
> That's a good question. I'm not sure how the record and replay backend
> deals with that, to be honest. But it does work, and I added a testcase
> specifically to test reversing the MOPS sequences, and it passes both on
> QEMU and FVP.

On x86 we require it. That's because we record the current value of all 
registers of interest, including PC, which means if you tried to 
disassemble many instructions and record them all, you'd be recording 
only the PC of the first instruction many times.  I haven't looked at 
the Arm tdep stuff for record but I can't imagine it would be too 
different. If I'm right, the test works because you don't try to 
reverse-stepi to the middle of the asm statement, you just look at the 
full state before and after.

If GDB will treat the block as always atomic, then I guess we don't need 
to save the PCs of every instruction, so this approach is fine, but if 
people are expected to be able to stepi in between the blocks, reverse 
should be able to do the same. If things are atomic, should we try to 
warn users who try to stepi/reverse-stepi through those blocks?


Sidenote, I haven't had time to look at the code yet, but personally, 
I'd like to see the test introduced at the same commit where support was 
added, because that would make it easier to bisect in the future, if 
necessary :)

-- 
Cheers,
Guinevere Larsen
She/Her/Hers