pussuw edited a comment on pull request #5731:
URL: https://github.com/apache/incubator-nuttx/pull/5731#issuecomment-1080564175
Can someone please explain to me how this change is supposed to work with
MMU and address environments ? Am I misunderstanding something ? The xcp.regs
are now allocated from the user task's stack memory, prior to this change they
were in the kernel's memory space.
Please note the following example
```
struct tcb_s *nexttcb = this_task();
#ifdef CONFIG_ARCH_ADDRENV
/* Make sure that the address environment for the previously
* running task is closed down gracefully (data caches dump,
* MMU flushed) and set up the address environment for the new
* thread at the head of the ready-to-run list.
*/
(void)group_addrenv(nexttcb);
#endif
/* Reset scheduler parameters */
nxsched_resume_scheduler(nexttcb);
/* Then switch contexts */
riscv_switchcontext(&rtcb->xcp.regs, nexttcb->xcp.regs);
```
If rtcb->xpc.regs points to the old task's stack, which resides in its
address environment, how can we perform a register save there ?
The old implementation saved the task context in the kernel space memory,
which is why it is safe to change the address environment as the memory for
xcp.regs[] exists in the kernel space and is always mapped ?
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