From: Martin Uecker <uecker@tugraz.at>
Date: Tue, 17 Sep 2024 09:37:29 +0000 (+0200)
Subject: c: fix crash when checking for compatibility of structures [PR116726]
X-Git-Tag: basepoints/gcc-16~5808
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9227a64495d5594613604573b72422e8e3722fc5;p=thirdparty%2Fgcc.git

c: fix crash when checking for compatibility of structures [PR116726]

When checking for compatibility of structure or union types in
tagged_types_tu_compatible_p, restore the old value of the pointer to
the top of the temporary cache after recursively calling comptypes_internal
when looping over the members of a structure of union.  While the next
iteration of the loop overwrites the pointer, I missed the fact that it can
be accessed again when types of function arguments are compared as part
of recursive type checking and the function is entered again.

	PR c/116726

gcc/c/ChangeLog:

	* c-typeck.cc (tagged_types_tu_compatible_p): Restore value
	of the cache after recursing into comptypes_internal.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr116726.c: New test.
---

diff --git a/gcc/c/c-typeck.cc b/gcc/c/c-typeck.cc
index 58b2724b39e..ba6d96d26b2 100644
--- a/gcc/c/c-typeck.cc
+++ b/gcc/c/c-typeck.cc
@@ -1686,8 +1686,11 @@ tagged_types_tu_compatible_p (const_tree t1, const_tree t2,
 	    data->anon_field = !DECL_NAME (s1);
 	    data->pointedto = false;
 
+	    const struct tagged_tu_seen_cache *cache = data->cache;
 	    data->cache = &entry;
-	    if (!comptypes_internal (TREE_TYPE (s1), TREE_TYPE (s2), data))
+	    bool ret = comptypes_internal (TREE_TYPE (s1), TREE_TYPE (s2), data);
+	    data->cache = cache;
+	    if (!ret)
 	      return false;
 
 	    tree st1 = TYPE_SIZE (TREE_TYPE (s1));
diff --git a/gcc/testsuite/gcc.dg/pr116726.c b/gcc/testsuite/gcc.dg/pr116726.c
new file mode 100644
index 00000000000..bb25efca586
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr116726.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-std=c23" } */
+
+struct s1 {
+  int f1;
+};
+struct s2 {
+  int f2;
+};
+struct s1 f(struct s2 *);
+
+struct s1 {
+  int f1;
+};
+struct s2 {
+  int f2;
+};
+struct s1 f(struct s2 *);