Generic function for obtaining the privilege stack bounds for x86

[maksimmasalski]

Describe the bug
arch.priv_stack_start is implemented only for ARM and ARC. Necessary to have a generic function for obtaining the privilege stack bounds for x86 too.
In other words, necessary to have an arch-neutral API for getting a pointer to the privilege mode stack, then there would not need to be any arch-specific code in this test case and it could be entirely cross-platform.

To Reproduce
Steps to reproduce the behavior:

1. Try to use thread->arch.priv_stack_start somewhere in the code
2. Build it for x86
3. It can't build for x86, because that feature not implemented for x86

Expected behavior
Obtaining the privilege stack bounds must be implemented for all architectures.

Impact
For x86 no generic function for obtaining the privilege stack bounds

Environment (please complete the following information):

• OS: Linux
• Toolchain Zephyr SDK 0.11.4
• Commit SHA d1f4a91

[maksimmasalski]

@andrewboie Could you take a look at that issue? So after solving it, I can finish my test cases PR #25323

[andrewboie]

yes will spend some time on this, thanks

[maksimmasalski]

@andrewboie Hello, any news from you regards that issue?

[enjiamai]

Hi @nashif @andyross , do we indeed need a function/interface like this? or we can implement this as a test util? thank you!

[andyross]

It doesn't seem like a bad API to have, but clearly we don't need it generically right now. In some architectures, there's no MMU state behind kernel stacks, so it's not necessarily something that matters to the hardware.

I guess if nothing else is should be part of CONFIG_THREAD_STACK_INFO, which is where we put this information (optionally) for apps that require it.