llext: userspace: clear cold segment descriptors when sections are absent

llext_manager_rm_mod_domain() removes the .cold and .coldrodata memory
partitions of a module from its domain if the corresponding
mctx->segment[] descriptor has a non-zero address. Those descriptors are
only ever populated by llext_manager_add_mod_domain() when the module
actually contains a .cold / .coldrodata section.

The module context array is allocated with rmalloc() (non-zeroing) and
llext_manager_mod_init() initialises every field except the segment[]
array. The LIB_MANAGER_TEXT/RODATA/DATA/BSS descriptors are filled in
during linking, but LIB_MANAGER_COLD / LIB_MANAGER_COLDRODATA are left
holding uninitialised heap data for any module that has no such section.

As a result, when such a module is freed, rm_mod_domain() sees a garbage
non-zero address and tries to remove a partition that was never added:

  <err> os.k_mem_domain_remove_partition: no matching partition found
  <err> lib_manager.llext_manager_rm_mod_domain: failed to remove
        .coldrodata memory partition: -2

Reproduced at end-of-stream of a DMIC capture (arecord -Dhw:0,4), whose
EQIIR / TDFB / DRC modules carry no .coldrodata section.

Make add_mod_domain() the sole owner of these descriptors: explicitly
zero them when the section is absent, so rm_mod_domain() only ever
removes partitions that were really added.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

Author: kv2019i

src/library_manager/llext_manager.c

@@ -952,6 +952,16 @@ static int llext_manager_add_mod_domain(struct lib_manager_module *mctx, struct
 			goto e_data;
 		mctx->segment[LIB_MANAGER_COLD].addr = (uintptr_t)text_addr + text_offset;
 		mctx->segment[LIB_MANAGER_COLD].size = shdr_cold.sh_size;
+	} else {
+		/*
+		 * No .cold section: make sure the descriptor is empty so that
+		 * llext_manager_rm_mod_domain() doesn't later try to remove a
+		 * partition that was never added. The module context is
+		 * allocated with rmalloc() and these fields are otherwise left
+		 * uninitialised.
+		 */
+		mctx->segment[LIB_MANAGER_COLD].addr = 0;
+		mctx->segment[LIB_MANAGER_COLD].size = 0;
 	}
 
 	if (rodata) {
@@ -964,6 +974,10 @@ static int llext_manager_add_mod_domain(struct lib_manager_module *mctx, struct
 			goto e_cold;
 		mctx->segment[LIB_MANAGER_COLDRODATA].addr = (uintptr_t)rodata_addr + rodata_offset;
 		mctx->segment[LIB_MANAGER_COLDRODATA].size = shdr_coldrodata.sh_size;
+	} else {
+		/* No .coldrodata section, see the comment above */
+		mctx->segment[LIB_MANAGER_COLDRODATA].addr = 0;
+		mctx->segment[LIB_MANAGER_COLDRODATA].size = 0;
 	}
 
 	return 0;