Imagine a simplified ARM Cortex-M3 system with a custom RTOS. The IVT is defined in assembly:
; Vector table entry for IRQ0 (system timer)
.word _ivt_stub_timer
...
The stub might look like:
_ivt_stub_timer:
push r0-r3, r12, lr
bl ivthandleinterrupt ; call C dispatcher
pop r0-r3, r12, lr
subs pc, lr, #4
And in C, the dispatcher:
// Array of registered interrupt callbacks static void (*isr_table[MAX_IRQS])(void);void register_isr(int irq_num, void (*handler)(void)) if (irq_num < MAX_IRQS) isr_table[irq_num] = handler;
void ivthandleinterrupt(unsigned int irq_number) // Call the registered ISR for this vector if (isr_table[irq_number]) isr_tableirq_number; ivthandleinterrupt
// Acknowledge interrupt to controller *(volatile uint32_t*)ICEOIR = irq_number;
But a more robust ivthandleinterrupt would query the hardware:
void ivthandleinterrupt(void) uint32_t active_irq = NVIC->IABR[0]; // simplified // Find lowest set bit -> IRQ number int irq_num = __builtin_ctz(active_irq);if (isr_table[irq_num]) isr_table[irq_num](); NVIC->ICPR[0] = (1 << irq_num); // clear pending
The IVT points to a tiny assembly routine that:
ivthandleinterrupt(vector, stacked_frame):
save_cpu_state()
if vector invalid: goto end
irq_info = lookup(vector)
source = detect_source(irq_info)
handler = irq_info.handler
if handler:
handled = handler(stacked_frame, irq_info.dev)
if not handled and irq_info.chained_handlers:
try chained handlers
if handler requested deferred_work:
schedule_deferred_work(irq_info.work)
send_eoi_to_controller(irq_info.controller)
end:
restore_cpu_state()
return_from_interrupt()
If you want platform-specific code (x86_64 assembly + C wrapper, or ARM Cortex-M C example), specify target architecture and calling convention and I will provide a compact sample.
Title: Deep Dive into ivthandleinterrupt: Tracing IRQs in the Embedded Kernel Imagine a simplified ARM Cortex-M3 system with a custom RTOS
Tags: Kernel, Interrupt Handling, Embedded Systems, Debugging, I/O Kit
Reading time: 4 minutes
If you’ve been digging through kernel panic logs, disassembling firmware, or working with low-level I/O on Apple’s embedded systems (like the T2 chip or iOS devices), you might have stumbled upon the cryptic function name ivthandleinterrupt.
At first glance, it looks like a typo of “interrupt handler.” But this symbol is a crucial piece of the puzzle for understanding how hardware interrupts are routed and processed. The stub might look like: _ivt_stub_timer: push r0-r3,
In this post, we’ll break down what ivthandleinterrupt is, how it fits into the interrupt flow, and how you can trace it for debugging or reverse engineering.