From: Marek Polacek <polacek@redhat.com>
Date: Tue, 14 Feb 2023 22:05:44 +0000 (-0500)
Subject: warn-access: wrong -Wdangling-pointer with labels [PR106080]
X-Git-Tag: releases/gcc-12.3.0~340
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=825a47f1bb9a42df65157d4dc0a11b2c054e97cc;p=thirdparty%2Fgcc.git

warn-access: wrong -Wdangling-pointer with labels [PR106080]

-Wdangling-pointer warns when the address of a label escapes.  This
causes grief in OCaml (<https://github.com/ocaml/ocaml/issues/11358>) as
well as in the kernel:
<https://bugzilla.kernel.org/show_bug.cgi?id=215851> because it uses

  #define _THIS_IP_  ({ __label__ __here; __here: (unsigned long)&&__here; })

to get the PC.  -Wdangling-pointer is documented to warn about pointers
to objects.  However, it uses is_auto_decl which checks DECL_P, but DECL_P
is also true for a label/enumerator/function declaration, none of which is
an object.  Rather, it should use auto_var_p which correctly checks VAR_P
and PARM_DECL.

	PR middle-end/106080

gcc/ChangeLog:

	* gimple-ssa-warn-access.cc (is_auto_decl): Remove.  Use auto_var_p
	instead.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wdangling-pointer-10.c: New test.
	* c-c++-common/Wdangling-pointer-9.c: New test.

(cherry picked from commit d482b20fd346482635a770281a164a09d608b058)
---

diff --git a/gcc/gimple-ssa-warn-access.cc b/gcc/gimple-ssa-warn-access.cc
index efe55dab9170..bac8675aa5a9 100644
--- a/gcc/gimple-ssa-warn-access.cc
+++ b/gcc/gimple-ssa-warn-access.cc
@@ -4308,15 +4308,6 @@ pass_waccess::check_call (gcall *stmt)
   check_nonstring_args (stmt);
 }
 
-
-/* Return true of X is a DECL with automatic storage duration.  */
-
-static inline bool
-is_auto_decl (tree x)
-{
-  return DECL_P (x) && !DECL_EXTERNAL (x) && !TREE_STATIC (x);
-}
-
 /* Check non-call STMT for invalid accesses.  */
 
 void
@@ -4345,7 +4336,7 @@ pass_waccess::check_stmt (gimple *stmt)
       while (handled_component_p (lhs))
 	lhs = TREE_OPERAND (lhs, 0);
 
-      if (is_auto_decl (lhs))
+      if (auto_var_p (lhs))
 	m_clobbers.remove (lhs);
       return;
     }
@@ -4365,7 +4356,7 @@ pass_waccess::check_stmt (gimple *stmt)
       while (handled_component_p (arg))
 	arg = TREE_OPERAND (arg, 0);
 
-      if (!is_auto_decl (arg))
+      if (!auto_var_p (arg))
 	return;
 
       gimple **pclobber = m_clobbers.get (arg);
@@ -4449,7 +4440,7 @@ void
 pass_waccess::check_dangling_uses (tree var, tree decl, bool maybe /* = false */,
 				   bool objref /* = false */)
 {
-  if (!decl || !is_auto_decl (decl))
+  if (!decl || !auto_var_p (decl))
     return;
 
   gimple **pclob = m_clobbers.get (decl);
@@ -4510,7 +4501,7 @@ pass_waccess::check_dangling_stores (basic_block bb,
       if (!m_ptr_qry.get_ref (lhs, stmt, &lhs_ref, 0))
 	continue;
 
-      if (is_auto_decl (lhs_ref.ref))
+      if (auto_var_p (lhs_ref.ref))
 	continue;
 
       if (DECL_P (lhs_ref.ref))
@@ -4555,7 +4546,7 @@ pass_waccess::check_dangling_stores (basic_block bb,
 	  || rhs_ref.deref != -1)
 	continue;
 
-      if (!is_auto_decl (rhs_ref.ref))
+      if (!auto_var_p (rhs_ref.ref))
 	continue;
 
       location_t loc = gimple_location (stmt);
diff --git a/gcc/testsuite/c-c++-common/Wdangling-pointer-10.c b/gcc/testsuite/c-c++-common/Wdangling-pointer-10.c
new file mode 100644
index 000000000000..ef553bdf2ce1
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wdangling-pointer-10.c
@@ -0,0 +1,12 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wdangling-pointer" } */
+
+struct S {
+  int x;
+};
+
+void g (int **p)
+{
+  struct S s = {};
+  *p = &s.x; /* { dg-warning "address of local variable" } */
+}
diff --git a/gcc/testsuite/c-c++-common/Wdangling-pointer-9.c b/gcc/testsuite/c-c++-common/Wdangling-pointer-9.c
new file mode 100644
index 000000000000..f6c92855404d
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wdangling-pointer-9.c
@@ -0,0 +1,9 @@
+/* PR middle-end/106080 */
+/* { dg-do compile } */
+/* { dg-options "-O2 -Wdangling-pointer" } */
+
+void
+foo (void **failaddr)
+{
+  *failaddr = ({ __label__ __here; __here: &&__here; }); /* { dg-bogus "address of local variable" } */
+}