nrf53_bsim: Get IPC shared memory buffer size from DT

boards/posix/nrf_bsim/CMakeLists.txt

@@ -35,8 +35,8 @@ target_sources(native_simulator INTERFACE
 	common/trace_hook.c
 )
 
-if (CONFIG_IPC_SERVICE)
-	target_sources(native_simulator INTERFACE
+if (CONFIG_IPC_SERVICE AND CONFIG_BOARD_NRF5340BSIM_NRF5340_CPUAPP)
+	zephyr_library_sources(
 		ipc_backend.c
 	)
 endif()

boards/posix/nrf_bsim/Kconfig.defconfig

@@ -6,7 +6,9 @@ config BUILD_OUTPUT_BIN
 	default n
 
 config BUILD_OUTPUT_EXE
-	default y
+	# When the IPC service is used, the net core image requires the application core image, as it needs
+	# access to its IPC buffer. Without it, the executable cannot be built.
+	default y if !(BOARD_NRF5340BSIM_NRF5340_CPUNET && IPC_SERVICE && (NATIVE_SIMULATOR_EXTRA_IMAGE_PATHS = ""))
 
 config OUTPUT_PRINT_MEMORY_USAGE
 	default n

boards/posix/nrf_bsim/ipc_backend.c

@@ -5,11 +5,23 @@
  */
 
 /*
- * This buffer is the shared memory buffer for the RPMSG IPC backed
- * in simulation.
- * It must be at last as large as the size defined in device tree, but as it will be compiled in
- * the native simulator runner context we cannot refer to DT itself to size it.
- * The default buffer for this target is defined in
- * boards/arm/nrf5340dk_nrf5340/nrf5340_shared_sram_planning_conf.dtsi
+ * Here we define the shared memory buffers for the RPMSG IPC back-end in simulation.
+ * In real HW, these are booked in RAM thru device tree configuration.
+ * In this simulated target, we just define them at build time to have the size defined
+ * in device tree.
+ *
+ * Note that this file is only compiled as part of the application core image, and therefore
+ * when the network core is built with the IPC service, we cannot produce an executable
+ * with the network core image alone, as we would lack this buffer during linking.
  */
-char IPC0_shm_buffer[65536];
+
+#include "nsi_cpu_if.h"
+#include <zephyr/device.h>
+
+#define DT_DRV_COMPAT zephyr_ipc_openamp_static_vrings
+
+#define DEFINE_BACKEND_BUFFER(i) \
+	NATIVE_SIMULATOR_IF \
+	char IPC##i##_shm_buffer[DT_REG_SIZE(DT_INST_PHANDLE(i, memory_region))];
+
+DT_INST_FOREACH_STATUS_OKAY(DEFINE_BACKEND_BUFFER)