device: add CONFIG_LLEXT_EXPORT_DEV_IDS_BY_HASH option

This new option allows to generate device names from the hash of the
devicetree node path, instead of the device's ordinal number. The
resulting names are stable across rebuilds.

Add a new test case to test this new option.

Signed-off-by: Luca Burelli <l.burelli@arduino.cc>

include/zephyr/device.h

@@ -101,9 +101,35 @@ typedef int16_t device_handle_t;
  * The ordinal used in this name can be mapped to the path by
  * examining zephyr/include/generated/zephyr/devicetree_generated.h.
  */
-#define Z_DEVICE_DT_DEV_ID(node_id) _CONCAT(dts_ord_, DT_DEP_ORD(node_id))
+#define Z_DEVICE_DT_DEP_ORD(node_id) _CONCAT(dts_ord_, DT_DEP_ORD(node_id))
 
-#if defined(CONFIG_LLEXT_EXPORT_DEVICES)
+/* Same as above, but uses the hash of the node path instead of the ordinal.
+ *
+ * The hash used in this name can be mapped to the path by
+ * examining zephyr/include/generated/zephyr/devicetree_generated.h.
+ */
+#define Z_DEVICE_DT_HASH(node_id) _CONCAT(dts_hash_, DT_HASH(node_id))
+
+/* By default, device identifiers are obtained using the dependency ordinal.
+ * When LLEXT_EXPORT_DEV_IDS_BY_HASH is defined, the main Zephyr binary exports
+ * DT identifiers via EXPORT_SYMBOL_NAMED as hashed versions of their paths.
+ * When matching extensions are built, that is what they need to look for.
+ *
+ * The ordinal or hash used in this name can be mapped to the path by
+ * examining zephyr/include/generated/zephyr/devicetree_generated.h.
+ */
+#if defined(LL_EXTENSION_BUILD) && defined(CONFIG_LLEXT_EXPORT_DEV_IDS_BY_HASH)
+#define Z_DEVICE_DT_DEV_ID(node_id) Z_DEVICE_DT_HASH(node_id)
+#else
+#define Z_DEVICE_DT_DEV_ID(node_id) Z_DEVICE_DT_DEP_ORD(node_id)
+#endif
+
+#if defined(CONFIG_LLEXT_EXPORT_DEV_IDS_BY_HASH)
+/* Export device identifiers by their hash */
+#define Z_DEVICE_EXPORT(node_id)                                               \
+	EXPORT_SYMBOL_NAMED(DEVICE_DT_NAME_GET(node_id),                       \
+			    STRINGIFY(DEVICE_NAME_GET(Z_DEVICE_DT_HASH(node_id))))
+#elif defined(CONFIG_LLEXT_EXPORT_DEVICES)
 /* Export device identifiers using the builtin name */
 #define Z_DEVICE_EXPORT(node_id) EXPORT_SYMBOL(DEVICE_DT_NAME_GET(node_id))
 #endif
@@ -175,8 +201,8 @@ typedef int16_t device_handle_t;
  *
  * This macro defines a @ref device that is automatically configured by the
  * kernel during system initialization. The global device object's name as a C
- * identifier is derived from the node's dependency ordinal. @ref device.name is
- * set to `DEVICE_DT_NAME(node_id)`.
+ * identifier is derived from the node's dependency ordinal or hash.
+ * @ref device.name is set to `DEVICE_DT_NAME(node_id)`.
  *
  * The device is declared with extern visibility, so a pointer to a global
  * device object can be obtained with `DEVICE_DT_GET(node_id)` from any source
@@ -208,7 +234,7 @@ typedef int16_t device_handle_t;
 			level, prio, api,                                      \
 			&Z_DEVICE_STATE_NAME(Z_DEVICE_DT_DEV_ID(node_id)),     \
 			__VA_ARGS__)                                           \
-	IF_ENABLED(CONFIG_LLEXT_EXPORT_DEVICES, (; Z_DEVICE_EXPORT(node_id)))  \
+	IF_ENABLED(CONFIG_LLEXT_EXPORT_DEVICES, (; Z_DEVICE_EXPORT(node_id)))
 
 /**
  * @brief Like DEVICE_DT_DEFINE(), but uses an instance of a `DT_DRV_COMPAT`

subsys/llext/Kconfig

@@ -73,6 +73,14 @@ config LLEXT_EXPORT_DEVICES
 	  When enabled, all Zephyr devices defined in the device tree are
 	  made available to llexts via the standard DT_ / DEVICE_* macros.
 
+config LLEXT_EXPORT_DEV_IDS_BY_HASH
+	bool "Use hash of device path in device name"
+	depends on LLEXT_EXPORT_DEVICES
+	help
+	  When enabled, exported device names are generated from a hash of
+	  the node path instead of an ordinal number. The resulting names
+	  are stable across rebuilds.
+
 config LLEXT_EXPORT_BUILTINS_BY_SLID
 	bool "Export built-in symbols to llexts via SLIDs"
 	help

tests/subsys/llext/simple/testcase.yaml

@@ -61,6 +61,14 @@ tests:
       - qemu_cortex_a53         # ARM Cortex-A53 (ARMv8-A ISA)
     extra_configs:
       - CONFIG_LLEXT_STORAGE_WRITABLE=n
+  llext.simple.devices_by_hash:
+    arch_allow: arm # Xtensa needs writable storage
+    filter: not CONFIG_MPU and not CONFIG_MMU and not CONFIG_SOC_SERIES_S32ZE
+    extra_configs:
+      - arch:arm:CONFIG_ARM_MPU=n
+      - arch:arm:CONFIG_ARM_AARCH32_MMU=n
+      - CONFIG_LLEXT_STORAGE_WRITABLE=n
+      - CONFIG_LLEXT_EXPORT_DEV_IDS_BY_HASH=y
   llext.simple.writable:
     arch_allow: arm xtensa
     integration_platforms: