arch: riscv: stacktrace: fix user thread stack bound check

[ycsin]

According to the riscv's arch.h:

 +------------+ <- thread.arch.priv_stack_start
 | Guard      | } Z_RISCV_STACK_GUARD_SIZE
 +------------+
 | Priv Stack | } CONFIG_PRIVILEGED_STACK_SIZE
 +------------+ <- thread.arch.priv_stack_start +
                   CONFIG_PRIVILEGED_STACK_SIZE +
                   Z_RISCV_STACK_GUARD_SIZE

The start of the privilege stack should be:

thread.arch.priv_stack_start + Z_RISCV_STACK_GUARD_SIZE

Instead of

thread.arch.priv_stack_start - CONFIG_PRIVILEGED_STACK_SIZE

For the end, use the same equation of top_of_priv_stack in the arch_user_mode_enter()

[npitre]

It might be better not to rely too much on CONFIG_PRIVILEGED_STACK_SIZE
directly as it ends up being subjected to extra rounding and alignment
through Z_STACK_PTR_ALIGN(). Might be worth to double-check against the
actual code in setup_thread_stack() and arch_user_mode_enter().

[ycsin]

Thanks for the insights

It might be better not to rely too much on CONFIG_PRIVILEGED_STACK_SIZE
directly as it ends up being subjected to extra rounding and alignment
through Z_STACK_PTR_ALIGN().

Should it be

Z_STACK_PTR_ALIGN(_current->arch.priv_stack_start + K_KERNEL_STACK_RESERVED + CONFIG_PRIVILEGED_STACK_SIZE);

instead? According to

zephyr/arch/riscv/core/thread.c

Lines 143 to 145 in 80ce7d2

	top_of_priv_stack = Z_STACK_PTR_ALIGN(_current->arch.priv_stack_start +
	K_KERNEL_STACK_RESERVED +
	CONFIG_PRIVILEGED_STACK_SIZE);

[npitre]

If it is the privileged/exception stack for user threads that you need then
arch_curr_cpu()->arch.user_exc_sp would be its top.

[npitre]

So yes, that's pretty much equivalent.

[npitre]

Maybe this ought to be abstracted in a single location eventually.
It is too easy to change one spot and miss the other otherwise.

[ycsin]

Maybe this ought to be abstracted in a single location eventually. It is too easy to change one spot and miss the other otherwise.

what if we store it somewhere, just like what we did with the stack_info?

[ycsin]

ping @fkokosinski @kgugala @tgorochowik

[fkokosinski]

LGTM