target/arm: New function armv7m_nvic_set_pending_lazyfp()

In the v7M architecture, if an exception is generated in the process
of doing the lazy stacking of FP registers, the handling of
possible escalation to HardFault is treated differently to the normal
approach: it works based on the saved information about exception
readiness that was stored in the FPCCR when the stack frame was
created. Provide a new function armv7m_nvic_set_pending_lazyfp()
which pends exceptions during lazy stacking, and implements
this logic.

This corresponds to the pseudocode TakePreserveFPException().

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20190416125744.27770-22-peter.maydell@linaro.org

hw/intc/armv7m_nvic.c

@@ -655,6 +655,102 @@ void armv7m_nvic_set_pending_derived(void *opaque, int irq, bool secure)
     do_armv7m_nvic_set_pending(opaque, irq, secure, true);
 }
 
+void armv7m_nvic_set_pending_lazyfp(void *opaque, int irq, bool secure)
+{
+    /*
+     * Pend an exception during lazy FP stacking. This differs
+     * from the usual exception pending because the logic for
+     * whether we should escalate depends on the saved context
+     * in the FPCCR register, not on the current state of the CPU/NVIC.
+     */
+    NVICState *s = (NVICState *)opaque;
+    bool banked = exc_is_banked(irq);
+    VecInfo *vec;
+    bool targets_secure;
+    bool escalate = false;
+    /*
+     * We will only look at bits in fpccr if this is a banked exception
+     * (in which case 'secure' tells us whether it is the S or NS version).
+     * All the bits for the non-banked exceptions are in fpccr_s.
+     */
+    uint32_t fpccr_s = s->cpu->env.v7m.fpccr[M_REG_S];
+    uint32_t fpccr = s->cpu->env.v7m.fpccr[secure];
+
+    assert(irq > ARMV7M_EXCP_RESET && irq < s->num_irq);
+    assert(!secure || banked);
+
+    vec = (banked && secure) ? &s->sec_vectors[irq] : &s->vectors[irq];
+
+    targets_secure = banked ? secure : exc_targets_secure(s, irq);
+
+    switch (irq) {
+    case ARMV7M_EXCP_DEBUG:
+        if (!(fpccr_s & R_V7M_FPCCR_MONRDY_MASK)) {
+            /* Ignore DebugMonitor exception */
+            return;
+        }
+        break;
+    case ARMV7M_EXCP_MEM:
+        escalate = !(fpccr & R_V7M_FPCCR_MMRDY_MASK);
+        break;
+    case ARMV7M_EXCP_USAGE:
+        escalate = !(fpccr & R_V7M_FPCCR_UFRDY_MASK);
+        break;
+    case ARMV7M_EXCP_BUS:
+        escalate = !(fpccr_s & R_V7M_FPCCR_BFRDY_MASK);
+        break;
+    case ARMV7M_EXCP_SECURE:
+        escalate = !(fpccr_s & R_V7M_FPCCR_SFRDY_MASK);
+        break;
+    default:
+        g_assert_not_reached();
+    }
+
+    if (escalate) {
+        /*
+         * Escalate to HardFault: faults that initially targeted Secure
+         * continue to do so, even if HF normally targets NonSecure.
+         */
+        irq = ARMV7M_EXCP_HARD;
+        if (arm_feature(&s->cpu->env, ARM_FEATURE_M_SECURITY) &&
+            (targets_secure ||
+             !(s->cpu->env.v7m.aircr & R_V7M_AIRCR_BFHFNMINS_MASK))) {
+            vec = &s->sec_vectors[irq];
+        } else {
+            vec = &s->vectors[irq];
+        }
+    }
+
+    if (!vec->enabled ||
+        nvic_exec_prio(s) <= exc_group_prio(s, vec->prio, secure)) {
+        if (!(fpccr_s & R_V7M_FPCCR_HFRDY_MASK)) {
+            /*
+             * We want to escalate to HardFault but the context the
+             * FP state belongs to prevents the exception pre-empting.
+             */
+            cpu_abort(&s->cpu->parent_obj,
+                      "Lockup: can't escalate to HardFault during "
+                      "lazy FP register stacking\n");
+        }
+    }
+
+    if (escalate) {
+        s->cpu->env.v7m.hfsr |= R_V7M_HFSR_FORCED_MASK;
+    }
+    if (!vec->pending) {
+        vec->pending = 1;
+        /*
+         * We do not call nvic_irq_update(), because we know our caller
+         * is going to handle causing us to take the exception by
+         * raising EXCP_LAZYFP, so raising the IRQ line would be
+         * pointless extra work. We just need to recompute the
+         * priorities so that armv7m_nvic_can_take_pending_exception()
+         * returns the right answer.
+         */
+        nvic_recompute_state(s);
+    }
+}
+
 /* Make pending IRQ active.  */
 void armv7m_nvic_acknowledge_irq(void *opaque)
 {

target/arm/cpu.h

@@ -2008,6 +2008,18 @@ void armv7m_nvic_set_pending(void *opaque, int irq, bool secure);
  * a different exception).
  */
 void armv7m_nvic_set_pending_derived(void *opaque, int irq, bool secure);
+/**
+ * armv7m_nvic_set_pending_lazyfp: mark this lazy FP exception as pending
+ * @opaque: the NVIC
+ * @irq: the exception number to mark pending
+ * @secure: false for non-banked exceptions or for the nonsecure
+ * version of a banked exception, true for the secure version of a banked
+ * exception.
+ *
+ * Similar to armv7m_nvic_set_pending(), but specifically for exceptions
+ * generated in the course of lazy stacking of FP registers.
+ */
+void armv7m_nvic_set_pending_lazyfp(void *opaque, int irq, bool secure);
 /**
  * armv7m_nvic_get_pending_irq_info: return highest priority pending
  *    exception, and whether it targets Secure state