From 8d6bd830f5f9c939e8565c0341a0c6c588834484 Mon Sep 17 00:00:00 2001
From: Martin Uecker <uecker@tugraz.at>
Date: Fri, 26 May 2023 11:19:01 +0200
Subject: [PATCH] c: -Wstringop-overflow for parameters with forward-declared
 sizes

Warnings from -Wstringop-overflow do not appear for parameters declared
as VLAs when the bound refers to a parameter forward declaration. This
is fixed by splitting the loop that passes through parameters into two,
first only recording the positions of all possible size expressions
and then processing the parameters.

PR c/109970

gcc/c-family:

	* c-attribs.cc (build_attr_access_from_parms): Split loop to first
	record all parameters.

gcc/testsuite:

	* gcc.dg/pr109970.c: New test.
---
 gcc/c-family/c-attribs.cc       |  9 +++++++++
 gcc/testsuite/gcc.dg/pr109970.c | 15 +++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/pr109970.c

diff --git a/gcc/c-family/c-attribs.cc b/gcc/c-family/c-attribs.cc
index 072cfb69147..e2792ca6898 100644
--- a/gcc/c-family/c-attribs.cc
+++ b/gcc/c-family/c-attribs.cc
@@ -5278,6 +5278,15 @@ build_attr_access_from_parms (tree parms, bool skip_voidptr)
       tree argtype = TREE_TYPE (arg);
       if (DECL_NAME (arg) && INTEGRAL_TYPE_P (argtype))
 	arg2pos.put (arg, argpos);
+    }
+
+  argpos = 0;
+  for (tree arg = parms; arg; arg = TREE_CHAIN (arg), ++argpos)
+    {
+      if (!DECL_P (arg))
+	continue;
+
+      tree argtype = TREE_TYPE (arg);
 
       tree argspec = DECL_ATTRIBUTES (arg);
       if (!argspec)
diff --git a/gcc/testsuite/gcc.dg/pr109970.c b/gcc/testsuite/gcc.dg/pr109970.c
new file mode 100644
index 00000000000..068c01f792d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr109970.c
@@ -0,0 +1,15 @@
+/* PR109970
+ * { dg-do compile }
+ * { dg-options "-Wstringop-overflow" }
+ * */
+
+void bar(int x, char buf[x]);
+void foo(int x; char buf[x], int x);
+
+int main()
+{
+	char buf[10];
+	bar(11, buf);	/* { dg-warning "accessing 11 bytes in a region of size 10" } */
+	foo(buf, 11);	/* { dg-warning "accessing 11 bytes in a region of size 10" } */
+}
+