hw/arm/boot: Make user not specifying a kernel not an error

Typically ARM boards will have some kind of flash which might contain
a boot ROM; it's therefore a valid use case to provide only an
image for the boot ROM and not require QEMU's internal boot loader
at all. Remove the fatal error if -kernel isn't specified.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1379980897-21277-2-git-send-email-peter.maydell@linaro.org

hw/arm/boot.c

@@ -354,8 +354,10 @@ void arm_load_kernel(ARMCPU *cpu, struct arm_boot_info *info)
 
     /* Load the kernel.  */
     if (!info->kernel_filename) {
-        fprintf(stderr, "Kernel image must be specified\n");
-        exit(1);
+        /* If no kernel specified, do nothing; we will start from address 0
+         * (typically a boot ROM image) in the same way as hardware.
+         */
+        return;
     }
 
     info->dtb_filename = qemu_opt_get(qemu_get_machine_opts(), "dtb");