Merge pull request #1778 from pguyot:w30/fix-empty-atom-esp32

Fix a bug where empty atom could not be decoded on esp32

(Note: before merging, the original 2 commits have been squashed
together)

These changes are made under both the "Apache 2.0" and the "GNU Lesser General
Public License 2.1 or later" license terms (dual license).

SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later

Author: bettio

CHANGELOG.md

@@ -71,6 +71,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Utilize reserved `phy_init` partition on ESP32 to store wifi calibration for faster connections.
 - Support for zero count in `lists:duplicate/2`.
 - packbeam: fix memory leak preventing building with address sanitizer
+- Fixed a bug where empty atom could not be created on some platforms, thus breaking receiving a message for a registered process from an OTP node.
 
 ## [0.6.7] - Unreleased
 

src/libAtomVM/atom_table.c

@@ -388,11 +388,13 @@ enum AtomTableEnsureAtomResult atom_table_ensure_atom(struct AtomTable *table, c
 
     if (opts & AtomTableCopyAtom) {
         uint8_t *buf = malloc(atom_len);
-        if (IS_NULL_PTR(buf)) {
-            SMP_UNLOCK(table);
-            return AtomTableEnsureAtomAllocFail;
+        if (atom_len > 0) {
+            if (IS_NULL_PTR(buf)) {
+                SMP_UNLOCK(table);
+                return AtomTableEnsureAtomAllocFail;
+            }
+            memcpy(buf, atom_data, atom_len);
         }
-        memcpy(buf, atom_data, atom_len);
         atom_data = buf;
     }
 

src/platforms/esp32/test/main/test_erl_sources/CMakeLists.txt

@@ -40,6 +40,7 @@ endfunction()
 compile_erlang(test_esp_partition)
 compile_erlang(test_file)
 compile_erlang(test_wifi_example)
+compile_erlang(test_list_to_atom)
 compile_erlang(test_list_to_binary)
 compile_erlang(test_md5)
 compile_erlang(test_crypto)
@@ -61,6 +62,7 @@ add_custom_command(
         test_esp_partition.beam
         test_file.beam
         test_wifi_example.beam
+        test_list_to_atom.beam
         test_list_to_binary.beam
         test_md5.beam
         test_crypto.beam
@@ -79,6 +81,7 @@ add_custom_command(
         "${CMAKE_CURRENT_BINARY_DIR}/test_esp_partition.beam"
         "${CMAKE_CURRENT_BINARY_DIR}/test_wifi_example.beam"
         "${CMAKE_CURRENT_BINARY_DIR}/test_file.beam"
+        "${CMAKE_CURRENT_BINARY_DIR}/test_list_to_atom.beam"
         "${CMAKE_CURRENT_BINARY_DIR}/test_list_to_binary.beam"
         "${CMAKE_CURRENT_BINARY_DIR}/test_md5.beam"
         "${CMAKE_CURRENT_BINARY_DIR}/test_crypto.beam"

src/platforms/esp32/test/main/test_erl_sources/test_list_to_atom.erl

@@ -0,0 +1,36 @@
+%
+% This file is part of AtomVM.
+%
+% Copyright 2025 Paul Guyot <[email protected]>
+%
+% Licensed under the Apache License, Version 2.0 (the "License");
+% you may not use this file except in compliance with the License.
+% You may obtain a copy of the License at
+%
+%    http://www.apache.org/licenses/LICENSE-2.0
+%
+% Unless required by applicable law or agreed to in writing, software
+% distributed under the License is distributed on an "AS IS" BASIS,
+% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+% See the License for the specific language governing permissions and
+% limitations under the License.
+%
+% SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
+%
+
+-module(test_list_to_atom).
+
+-export([start/0]).
+
+start() ->
+    ok = test_empty_list_to_atom(),
+    ok.
+
+test_empty_list_to_atom() ->
+    Atom = erlang:list_to_atom(id([])),
+    true = is_atom(id(Atom)),
+    [] = erlang:atom_to_list(id(Atom)),
+    ok.
+
+id(X) ->
+    X.

src/platforms/esp32/test/main/test_main.c

@@ -289,6 +289,12 @@ TEST_CASE("test_file", "[test_run]")
 }
 #endif
 
+TEST_CASE("test_list_to_atom", "[test_run]")
+{
+    term ret_value = avm_test_case("test_list_to_atom.beam");
+    TEST_ASSERT(ret_value == OK_ATOM);
+}
+
 TEST_CASE("test_list_to_binary", "[test_run]")
 {
     term ret_value = avm_test_case("test_list_to_binary.beam");