Dynamic interrupt does not work with multi-level interrupts

[dcpleung]

There is a potential for writing into memory past _sw_isr_table[] due to the interrupt encoding with multi-level interrupts and dynamic interrupts. This is because z_isr_install() in arch/common/sw_isr_common.c simply takes the input irq to calculate a linear index to _sw_isr_table[]. However, in reality, the elements after 1st level interrupts are sparsely populated and no longer linear. For example:

• Each level has 32 IRQs.
• There is one 2nd level interrupts out of Bluetooth: ATT: Respond with not support error for unknown PDUs #6 of 1st level.
• So the interrupt encoding of the 7th IRQ on 2nd level would be '0x0806'.
• z_isr_install() sets _sw_isr_table[2054] with the ISR.
• However, due to there is only one 2nd level interrupt, the index should be 39 (32 + 7).
• Also note that the size of _sw_isr_table is only 64 (32 + 32).

[aescolar]

CC @andyross @andrewboie

[dcpleung]

Fixed in commit 0fb4382