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armv7m: Escalate exceptions to HardFault if necessary

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The v7M exception architecture requires that if a synchronous
exception cannot be taken immediately (because it is disabled
or at too low a priority) then it should be escalated to
HardFault (and the HardFault exception is then taken).
Implement this escalation logic.

Signed-off-by: Michael Davidsaver <mdavidsaver@gmail.com>
[PMM: extracted from another patch]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
This commit is contained in:
Michael Davidsaver 2017-02-28 12:08:17 +00:00 committed by Peter Maydell
parent 7c14b3ac07
commit a73c98e159
2 changed files with 53 additions and 2 deletions
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53
hw/intc/armv7m_nvic.c
View File

@ -352,6 +352,59 @@ void armv7m_nvic_set_pending(void *opaque, int irq)
vec = &s->vectors[irq];
trace_nvic_set_pending(irq, vec->enabled, vec->prio);
if (irq >= ARMV7M_EXCP_HARD && irq < ARMV7M_EXCP_PENDSV) {
/* If a synchronous exception is pending then it may be
* escalated to HardFault if:
* * it is equal or lower priority to current execution
* * it is disabled
* (ie we need to take it immediately but we can't do so).
* Asynchronous exceptions (and interrupts) simply remain pending.
*
* For QEMU, we don't have any imprecise (asynchronous) faults,
* so we can assume that PREFETCH_ABORT and DATA_ABORT are always
* synchronous.
* Debug exceptions are awkward because only Debug exceptions
* resulting from the BKPT instruction should be escalated,
* but we don't currently implement any Debug exceptions other
* than those that result from BKPT, so we treat all debug exceptions
* as needing escalation.
*
* This all means we can identify whether to escalate based only on
* the exception number and don't (yet) need the caller to explicitly
* tell us whether this exception is synchronous or not.
*/
int running = nvic_exec_prio(s);
bool escalate = false;
if (vec->prio >= running) {
trace_nvic_escalate_prio(irq, vec->prio, running);
escalate = true;
} else if (!vec->enabled) {
trace_nvic_escalate_disabled(irq);
escalate = true;
}
if (escalate) {
if (running < 0) {
/* We want to escalate to HardFault but we can't take a
* synchronous HardFault at this point either. This is a
* Lockup condition due to a guest bug. We don't model
* Lockup, so report via cpu_abort() instead.
*/
cpu_abort(&s->cpu->parent_obj,
"Lockup: can't escalate %d to HardFault "
"(current priority %d)\n", irq, running);
}
/* We can do the escalation, so we take HardFault instead */
irq = ARMV7M_EXCP_HARD;
vec = &s->vectors[irq];
s->cpu->env.v7m.hfsr |= R_V7M_HFSR_FORCED_MASK;
}
}
if (!vec->pending) {
vec->pending = 1;
nvic_irq_update(s);

2
target/arm/helper.c
View File

@ -6106,8 +6106,6 @@ void arm_v7m_cpu_do_interrupt(CPUState *cs)
/* For exceptions we just mark as pending on the NVIC, and let that
handle it. */
/* TODO: Need to escalate if the current priority is higher than the
one we're raising. */
switch (cs->exception_index) {
case EXCP_UDEF:
armv7m_nvic_set_pending(env->nvic, ARMV7M_EXCP_USAGE);