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, 18 insertions, 0 deletions

diff --git a/target/arm/cpu.c b/target/arm/cpu.c
index ab047b9402..e1de45e904 100644
--- a/target/arm/cpu.c
+++ b/target/arm/cpu.c
@@ -767,6 +767,24 @@ static void arm_cpu_realizefn(DeviceState *dev, Error **errp)
         return;
     }
 
+#ifndef CONFIG_USER_ONLY
+    /* The NVIC and M-profile CPU are two halves of a single piece of
+     * hardware; trying to use one without the other is a command line
+     * error and will result in segfaults if not caught here.
+     */
+    if (arm_feature(env, ARM_FEATURE_M)) {
+        if (!env->nvic) {
+            error_setg(errp, "This board cannot be used with Cortex-M CPUs");
+            return;
+        }
+    } else {
+        if (env->nvic) {
+            error_setg(errp, "This board can only be used with Cortex-M CPUs");
+            return;
+        }
+    }
+#endif
+
     cpu_exec_realizefn(cs, &local_err);
     if (local_err != NULL) {
         error_propagate(errp, local_err);