Fix string allocation when slot size < 40 bytes

We need to allocate at least sizeof(struct RString) when the string is
embedded on garbage collectors that support slot sizes less than 40 bytes.

1 files changed, 3 insertions, 1 deletions

diff --git a/string.c b/string.c
index fa6ce7f3ec..2a250cc69d 100644
--- a/string.c
+++ b/string.c
@@ -242,7 +242,9 @@ rb_str_reembeddable_p(VALUE str)
 static inline size_t
 rb_str_embed_size(long capa)
 {
-    return offsetof(struct RString, as.embed.ary) + capa;
+    size_t size = offsetof(struct RString, as.embed.ary) + capa;
+    if (size < sizeof(struct RString)) size = sizeof(struct RString);
+    return size;
 }
 
 size_t