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Re: C PATCH to reject va_arg (ap, void) (PR c/65901)


On 04/27/2015 11:30 AM, Marek Polacek wrote:
As reported in the PR, va_arg (ap, void) probably doesn't make any sense and
should be rejected thus.  cc1plus and clang reject va_arg with an incomplete
type.  This patch makes cc1 reject it as well.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2015-04-27  Marek Polacek  <polacek@redhat.com>

	PR c/65901
	* c-typeck.c (c_build_va_arg): Require TYPE be a complete type.

	* gcc.c-torture/compile/pr48767.c (foo): Add dg-error.
	* gcc.dg/pr65901.c: New test.

diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
index 91735b5..c58e918 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -12648,6 +12648,11 @@ c_build_va_arg (location_t loc, tree expr, tree type)
    if (warn_cxx_compat && TREE_CODE (type) == ENUMERAL_TYPE)
      warning_at (loc, OPT_Wc___compat,
  		"C++ requires promoted type, not enum type, in %<va_arg%>");
+  if (type == error_mark_node || !COMPLETE_TYPE_P (type))
+    {
+      c_incomplete_type_error (NULL_TREE, type);

The error message in the test cases below isn't quite right.
The type of the aggregates isn't undefined, it's incomplete.
Looking at the function, I wonder if the first argument
should be EXPR rather than than NULL_TREE? Alternatively,
experimenting with other cases where GCC diagnoses invalid
uses of incomplete type, I see that it issues:

  "invalid application of %qs to incomplete type %qT"

which might work even better here since we could name the
expression (va_arg).

Martin

+      return error_mark_node;
+    }
    return build_va_arg (loc, expr, type);
  }

diff --git gcc/testsuite/gcc.c-torture/compile/pr48767.c gcc/testsuite/gcc.c-torture/compile/pr48767.c
index 66cb348..c8fef35 100644
--- gcc/testsuite/gcc.c-torture/compile/pr48767.c
+++ gcc/testsuite/gcc.c-torture/compile/pr48767.c
@@ -3,5 +3,5 @@
  void
  foo (__builtin_va_list ap)
  {
-  __builtin_va_arg (ap, void);
+  __builtin_va_arg (ap, void);  /* { dg-error "invalid use of void expression" } */
  }
diff --git gcc/testsuite/gcc.dg/pr65901.c gcc/testsuite/gcc.dg/pr65901.c
index e69de29..8708a1e 100644
--- gcc/testsuite/gcc.dg/pr65901.c
+++ gcc/testsuite/gcc.dg/pr65901.c
@@ -0,0 +1,16 @@
+/* PR c/65901 */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+struct S;
+enum E;
+union U;
+
+void
+foo (__builtin_va_list ap)
+{
+  __builtin_va_arg (ap, void);  /* { dg-error "invalid use of void expression" } */
+  __builtin_va_arg (ap, struct S);  /* { dg-error "invalid use of undefined type" } */
+  __builtin_va_arg (ap, enum E);  /* { dg-error "invalid use of undefined type" } */
+  __builtin_va_arg (ap, union U);  /* { dg-error "invalid use of undefined type" } */
+}

	Marek



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