llext: make EXPORT_SYMBOL() universal

Currently LLEXT has two ways to export symbols:
EXPORT_SYMBOL() to exort symbols from the main firmware to extensions
LL_EXTENSION_SYMBOL() to export symbols from extensions
but it is possible to write code, that needs to export symbols
regardless of whether it is built into the main image or an
extension. And in fact there's no real need in two distinct macros -
we can use one for both cases and recognise at build time which
direction exporting is happening. This patch extends EXPORT_SYMBOL()
to also work from extensions.

Signed-off-by: Guennadi Liakhovetski <[email protected]>

Author: lyakh

include/zephyr/llext/symbol.h

@@ -87,6 +87,26 @@ struct llext_symtable {
 };
 
 
+/**
+ * @brief Exports a symbol from an extension to the base image
+ *
+ * This macro can be used in extensions to add a symbol (function or object)
+ * to the extension's exported symbol table, so that it may be referenced by
+ * the base image.
+ *
+ * @param x Extension symbol to export to the base image
+ */
+#if defined(CONFIG_LLEXT) && defined(LL_EXTENSION_BUILD)
+#define LL_EXTENSION_SYMBOL(x)							\
+	static const struct llext_const_symbol					\
+			Z_GENERIC_SECTION(".exported_sym") __used		\
+			x ## _sym = {						\
+		.name = STRINGIFY(x), .addr = (const void *)&x,			\
+	}
+#else
+#define LL_EXTENSION_SYMBOL(x)
+#endif
+
 /**
  * @brief Export a constant symbol to extensions
  *
@@ -96,7 +116,9 @@ struct llext_symtable {
  *
  * @param x Symbol to export to extensions
  */
-#if defined(CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID)
+#if defined(LL_EXTENSION_BUILD)
+#define EXPORT_SYMBOL(x) LL_EXTENSION_SYMBOL(x)
+#elif defined(CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID)
 #define EXPORT_SYMBOL(x)							\
 	static const char Z_GENERIC_SECTION("llext_exports_strtab") __used	\
 		x ## _sym_name[] = STRINGIFY(x);				\
@@ -112,26 +134,6 @@ struct llext_symtable {
 #define EXPORT_SYMBOL(x)
 #endif
 
-/**
- * @brief Exports a symbol from an extension to the base image
- *
- * This macro can be used in extensions to add a symbol (function or object)
- * to the extension's exported symbol table, so that it may be referenced by
- * the base image.
- *
- * @param x Extension symbol to export to the base image
- */
-#if defined(CONFIG_LLEXT) && defined(LL_EXTENSION_BUILD)
-#define LL_EXTENSION_SYMBOL(x)							\
-	static const struct llext_const_symbol					\
-			Z_GENERIC_SECTION(".exported_sym") __used		\
-			x ## _sym = {						\
-		.name = STRINGIFY(x), .addr = (const void *)&x,			\
-	}
-#else
-#define LL_EXTENSION_SYMBOL(x)
-#endif
-
 /**
  * @}
  */