arm: Don't crash if user tries to use a Cortex-M CPU without an NVIC

The Cortex-M CPU and its NVIC are two intimately intertwined parts of
the same hardware; it is not possible to use one without the other.
Unfortunately a lot of our board models don't do any sanity checking
on the CPU type the user asks for, so a command line like
    qemu-system-arm -M versatilepb -cpu cortex-m3
will create an M3 without an NVIC, and coredump immediately.
In the other direction, trying a non-M-profile CPU in an M-profile
board won't blow up, but doesn't do anything useful either:
    qemu-system-arm -M lm3s6965evb -cpu arm926

Add some checking in the NVIC and CPU realize functions that the
user isn't trying to use an NVIC without an M-profile CPU or
an M-profile CPU without an NVIC, so we can produce a helpful
error message rather than a core dump.

Fixes: https://bugs.launchpad.net/qemu/+bug/1766896
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-id: 20180601160355.15393-1-peter.maydell@linaro.org

1 files changed, 5 insertions, 1 deletions

diff --git a/hw/intc/armv7m_nvic.c b/hw/intc/armv7m_nvic.c
index c51151fa8a..661be8878a 100644
--- a/hw/intc/armv7m_nvic.c
+++ b/hw/intc/armv7m_nvic.c
@@ -2183,7 +2183,11 @@ static void armv7m_nvic_realize(DeviceState *dev, Error **errp)
     int regionlen;
 
     s->cpu = ARM_CPU(qemu_get_cpu(0));
-    assert(s->cpu);
+
+    if (!s->cpu || !arm_feature(&s->cpu->env, ARM_FEATURE_M)) {
+        error_setg(errp, "The NVIC can only be used with a Cortex-M CPU");
+        return;
+    }
 
     if (s->num_irq > NVIC_MAX_IRQ) {
         error_setg(errp, "num-irq %d exceeds NVIC maximum", s->num_irq);