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arch: arm: aarch32: Fix exception exit failures

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This commit fixes the following bugs in the AArch32 z_arm_exc_exit
routine:

1. Invalid return address when calling `z_arm_pendsv` from the
   exception-specific mode

2. Caller-saved register is referenced after a call to `z_arm_pendsv`

For more details, refer to the issue #31511.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>
This commit is contained in:
Stephanos Ioannidis 2021-01-22 15:17:22 +09:00 committed by Anas Nashif
parent d86fdb2154
commit c00169daba
1 changed files with 9 additions and 1 deletions
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10
arch/arm/core/aarch32/cortex_a_r/exc_exit.S
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@ -131,10 +131,18 @@ SECTION_SUBSEC_FUNC(TEXT, _HandlerModeExit, z_arm_exc_exit)
/* Clean up exception stack frame */
add sp, #32
/* Switch in the next scheduled thread */
/*
* Switch in the next scheduled thread.
*
* Note that z_arm_pendsv must be called in the SVC mode because it
* switches to the SVC mode during context switch and returns to the
* caller using lr_svc.
*/
cps #MODE_SVC
bl z_arm_pendsv
/* Decrement exception nesting count */
ldr r3, =_kernel
ldr r0, [r3, #_kernel_offset_to_nested]
sub r0, r0, #1
str r0, [r3, #_kernel_offset_to_nested]