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possible fix for pre ARMv7 ASM interrupt handler #143

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Merged
jonathanpallant merged 1 commit into from
Mar 5, 2026
Merged

possible fix for pre ARMv7 ASM interrupt handler #143

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2 changes: 2 additions & 0 deletions aarch32-rt/src/arch_v4/interrupt.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,6 +21,7 @@ core::arch::global_asm!(
mrs lr, spsr // The hardware has copied the interrupted task's CPSR to SPSR_irq - grab it and
push {{ lr }} // save it to IRQ stack using LR
msr cpsr_c, {sys_mode} // switch to system mode so we can handle another interrupt (because if we interrupt irq mode we trash our own shadow registers)
push {{ lr }} // Save LR of system mode before using it for stack alignment
mov lr, sp // align SP down to eight byte boundary using LR
and lr, lr, 7 //
sub sp, lr // SP now aligned - only push 64-bit values from here
Expand All @@ -34,6 +35,7 @@ core::arch::global_asm!(
r#"
pop {{ r0-r3, r12, lr }} // restore alignment amount (in LR) and preserved registers
add sp, lr // restore SP alignment using LR
pop {{ lr }} // Restore the actual link register of system mode.
msr cpsr_c, {irq_mode} // switch back to IRQ mode (with IRQ masked)
pop {{ lr }} // load and restore SPSR using LR
msr spsr, lr //
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