py/misc: Change sizeof to offsetof for variable-length alloc.

This fixes the case where e.g.

    struct foo_t {
      mp_obj_t x;
      uint16_t y;
      char buf[];
    };

will have `sizeof(struct foo_t)==8`, but `offsetof(struct foo_t, buf)==6`.

When computing the size to allocate for `m_new_obj_var` we need to use
offsetof to avoid over-allocating. This is important especially when it
might cause it to spill over into another GC block.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/py/objnamedtuple.c b/py/objnamedtuple.c
index 75e21494b..e586f0894 100644
--- a/py/objnamedtuple.c
+++ b/py/objnamedtuple.c
@@ -143,7 +143,7 @@ STATIC mp_obj_t namedtuple_make_new(const mp_obj_type_t *type_in, size_t n_args,
 }
 
 mp_obj_namedtuple_type_t *mp_obj_new_namedtuple_base(size_t n_fields, mp_obj_t *fields) {
-    mp_obj_namedtuple_type_t *o = m_new_obj_var0(mp_obj_namedtuple_type_t, qstr, n_fields);
+    mp_obj_namedtuple_type_t *o = m_new_obj_var0(mp_obj_namedtuple_type_t, fields, qstr, n_fields);
     o->n_fields = n_fields;
     for (size_t i = 0; i < n_fields; i++) {
         o->fields[i] = mp_obj_str_get_qstr(fields[i]);