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riscv: drop user stack guard area when using separate privileged stacks

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A separate privileged stack is used when CONFIG_GEN_PRIV_STACKS=y. The
main stack guard area is no longer needed and can be made available to
the application upon transitioning to user mode. And that's actually
required if we want a naturally aligned power-of-two buffer to let the
PMP map a NAPOT entry on it which is the whole point of having this
CONFIG_PMP_POWER_OF_TWO_ALIGNMENT option in the first place.

Signed-off-by: Nicolas Pitre <npitre@baylibre.com>
This commit is contained in:
Nicolas Pitre 2022-05-14 15:59:57 -04:00 • committed by Carles Cufí
commit 92409f36de
2 changed files with 19 additions and 1 deletions
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3
arch/riscv/core/thread.c
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@ -216,6 +216,9 @@ FUNC_NORETURN void arch_user_mode_enter(k_thread_entry_t user_entry,
#ifdef CONFIG_GEN_PRIV_STACKS
_current->arch.priv_stack_start =
(ulong_t)z_priv_stack_find(_current->stack_obj);
/* remove the stack guard from the main stack */
_current->stack_info.start -= K_THREAD_STACK_RESERVED;
_current->stack_info.size += K_THREAD_STACK_RESERVED;
#else
_current->arch.priv_stack_start = (ulong_t)_current->stack_obj;
#endif /* CONFIG_GEN_PRIV_STACKS */