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Incorrect logic in ARMv7M interrupt handler
On ARMv7M interrupts handlers will be called even if emulated code executes "cpsid i" instruction.
Underlying cause described below:
In cpu-exec.c:cpu_exec there is a block of code that determines if an interrupt should be raised or not:
/* ARMv7-M interrupt return works by loading a magic value
into the PC. On real hardware the load causes the
return to occur. The qemu implementation performs the
jump normally, then does the exception return when the
CPU tries to execute code at the magic address.
This will cause the magic PC value to be pushed to
the stack if an interrupt occurred at the wrong time.
We avoid this by disabling interrupts when
pc contains a magic address. */
if (interrupt_request & CPU_INTERRUPT_HARD
&& ((IS_M(env) && env->regs[15] < 0xfffffff0)
|| !(env->uncached_cpsr & CPSR_I))) {
env->exception_index = EXCP_IRQ;
cc->do_interrupt(cpu);
next_tb = 0;
}
I'm not convinced the logic is correct.
The logic for ARMv7M should be:
If an interrupt is pending (interrupt_request & CPU_INTERRUPT_HARD)
AND
Interrupts are not disabled ( !(env->uncached_cpsr & CPSR_I) )
AND
PC doesn't have a magic value (env->regs[15] < 0xfffffff0)
The current logic seems fires the interrupt if interrupts are enabled OR the PC isn't magic, which is basically all the time.
I'm not sure what the cleanest patch for this would be.
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