Merge pull request #548 from dhalbert/3.0_alloca_problem_issue_521

alloca seems buggy on M4

1 files changed, 3 insertions, 2 deletions

diff --git a/py/runtime.c b/py/runtime.c
index cbec82f17..7a16e4a1b 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -1428,9 +1428,10 @@ import_error:
     mp_load_method_maybe(module, MP_QSTR___name__, dest);
     size_t pkg_name_len;
     const char *pkg_name = mp_obj_str_get_data(dest[0], &pkg_name_len);
-
     const uint dot_name_len = pkg_name_len + 1 + qstr_len(name);
-    char *dot_name = alloca(dot_name_len);
+    // Previously dot_name was created using alloca(), but that caused run-time crashes on M4 due to
+    // stack corruption (compiler bug, it appears), so use an array instead.
+    char dot_name[dot_name_len];
     memcpy(dot_name, pkg_name, pkg_name_len);
     dot_name[pkg_name_len] = '.';
     memcpy(dot_name + pkg_name_len + 1, qstr_str(name), qstr_len(name));