llext: fix save-restore with no initialized modules

LLEXT save-restore to DRAM had a bug: if the DSP is powered off with
loaded LLEXT modules, none of which was used, context restoration was
performed incorrectly, leading to inability to use LLEXT after the
next boot. This patch fixes that bug.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>

Author: lyakh

src/library_manager/llext_manager_dram.c

@@ -23,6 +23,7 @@ struct lib_manager_dram_storage {
 	struct llext_elf_sect_map *sect;
 	struct llext_symbol *sym;
 	unsigned int n_llext;
+	unsigned int n_mod;
 };
 
 /*
@@ -147,6 +148,8 @@ int llext_manager_store_to_dram(void)
 	}
 
 	lib_manager_dram.n_llext = n_llext;
+	lib_manager_dram.n_mod = n_mod;
+
 	/* Make sure, that the data is actually in the DRAM, not just in data cache */
 	dcache_writeback_region((__sparse_force void __sparse_cache *)&lib_manager_dram,
 				sizeof(lib_manager_dram));
@@ -162,26 +165,33 @@ int llext_manager_restore_from_dram(void)
 
 	struct ext_library *_ext_lib = ext_lib_get();
 	unsigned int i, j, k, n_mod, n_llext, n_sect, n_sym;
+	struct llext_loader **ldr;
+	struct llext **llext;
 
-	if (!lib_manager_dram.n_llext || !lib_manager_dram.ctx) {
+	if (!lib_manager_dram.n_mod || !lib_manager_dram.ctx) {
 		tr_dbg(&lib_manager_tr, "No modules saved");
 		dcache_writeback_region((__sparse_force void __sparse_cache *)&lib_manager_dram,
 					sizeof(lib_manager_dram));
 		return 0;
 	}
 
-	/* arrays of pointers for llext_restore() */
-	void **ptr_array = rmalloc(SOF_MEM_FLAG_KERNEL,
-				   sizeof(*ptr_array) * lib_manager_dram.n_llext * 2);
-
-	if (!ptr_array)
-		return -ENOMEM;
-
-	struct llext_loader **ldr = (struct llext_loader **)ptr_array;
-	struct llext **llext = (struct llext **)(ptr_array + lib_manager_dram.n_llext);
-
 	*_ext_lib = lib_manager_dram.ext_lib;
 
+	if (lib_manager_dram.n_llext) {
+		/* arrays of pointers for llext_restore() */
+		void **ptr_array = rmalloc(SOF_MEM_FLAG_KERNEL,
+					   sizeof(*ptr_array) * lib_manager_dram.n_llext * 2);
+
+		if (!ptr_array)
+			return -ENOMEM;
+
+		ldr = (struct llext_loader **)ptr_array;
+		llext = (struct llext **)(ptr_array + lib_manager_dram.n_llext);
+	} else {
+		ldr = NULL;
+		llext = NULL;
+	}
+
 	/* The external loop walks all the libraries */
 	for (i = 0, j = 0, n_mod = 0, n_llext = 0, n_sect = 0, n_sym = 0;
 	     i < ARRAY_SIZE(_ext_lib->desc); i++) {
@@ -262,26 +272,28 @@ int llext_manager_restore_from_dram(void)
 		_ext_lib->desc[i] = ctx;
 	}
 
-	/* Let Zephyr restore extensions and its own internal bookkeeping */
-	int ret = llext_restore(llext, ldr, lib_manager_dram.n_llext);
+	if (lib_manager_dram.n_llext) {
+		/* Let Zephyr restore extensions and its own internal bookkeeping */
+		int ret = llext_restore(llext, ldr, lib_manager_dram.n_llext);
 
-	if (ret < 0) {
-		tr_err(&lib_manager_tr, "Zephyr failed to restore: %d", ret);
-		goto nomem;
-	}
+		if (ret < 0) {
+			tr_err(&lib_manager_tr, "Zephyr failed to restore: %d", ret);
+			goto nomem;
+		}
 
-	/* Rewrite to correct LLEXT pointers, created by Zephyr */
-	for (i = 0, n_llext = 0; i < ARRAY_SIZE(_ext_lib->desc); i++) {
-		struct lib_manager_mod_ctx *ctx = _ext_lib->desc[i];
+		/* Rewrite to correct LLEXT pointers, created by Zephyr */
+		for (i = 0, n_llext = 0; i < ARRAY_SIZE(_ext_lib->desc); i++) {
+			struct lib_manager_mod_ctx *ctx = _ext_lib->desc[i];
 
-		if (!ctx)
-			continue;
+			if (!ctx)
+				continue;
 
-		struct lib_manager_module *mod = ctx->mod;
+			struct lib_manager_module *mod = ctx->mod;
 
-		for (k = 0; k < ctx->n_mod; k++) {
-			if (mod[k].llext)
-				mod[k].llext = llext[n_llext++];
+			for (k = 0; k < ctx->n_mod; k++) {
+				if (mod[k].llext)
+					mod[k].llext = llext[n_llext++];
+			}
 		}
 	}