Figured it out; turns out my code to align the stack so I could make calls without raising exceptions was messing up and corrupting the stack-pointer.
Running the -O2 code now makes the clock run a bit too quickly - the calibration may have a minor issue. I'll fix that up and send patches tomorrow or Monday hopefully. I'll be traveling Tuesday, so I'd appreciate if we can get them merged upstream Monday itself - I'm okay to have a call and walk someone through the patches and whatnot if need be. Cheers! On Sun, Aug 12, 2018 at 1:25 AM, Amaan Cheval <amaan.che...@gmail.com> wrote: > Hi! > > In the process of cleaning my work up, I've run into an odd problem > which only shows up when I set the optimization level to -O2. At -O0, > it's perfectly fine. > > The issue is that somehow execution ends up at address 0x0. > > This likely happens due to a _CPU_Context_switch, where the rsp is set > to a corrupted value, leading to a corrupt (i.e. 0) return address at > the end of the context switch. > > What's curious is that this corruption _seems_ to occur in > _ISR_Handler's call to _Thread_Dispatch, by somehow messing the value > of rsp up - I honestly don't know this for sure because gdb says one > thing (i.e. that rsp = 0), but setting up some code (cmpq $0, rsp) to > check this seems to say rsp is non-zero, at least. > > This is an odd heisenbug I'd like to investigate for sure - I just > thought I'd shoot this email out because: > > - If I can't figure it out tomorrow, soon, I'll just drop it so I can > create more logical commits to send as patches upstream (thereby > leaving -O0 upstream, at least temporarily) > > - If anyone's seen an odd stack corruption like this, or has any > advice on debugging it, could you let me know? I suspect something > like interrupting tasks which ought not to be interrupted (perhaps I > forgot to implement some kind of "CPU_ISR_Disable") - is there > anything you can think of of that sort? > > Also, here's a Github PR like last time with all the work (just for > the overall changes, not the specific commits!). I'd appreciate a > quick review if anyone could - sorry about sending this out over the > weekend! I've had a surprising share of Heisenbugs with QEMU in the > past week. > > https://github.com/AmaanC/rtems-gsoc18/pull/3/files _______________________________________________ devel mailing list devel@rtems.org http://lists.rtems.org/mailman/listinfo/devel
