On Mon, Jan 13, 2014 at 05:48:59PM +0100, Marek Polacek wrote:
> The patch will need some tweaking, I realized that e.g. for struct S {
> union {}; }; it doesn't do the right thing...
Done in the patch below. CCing Jason for the C++ part. Does this
look sane now?
Regtested/bootstrapped on x86_64.
2014-01-13 Marek Polacek <pola...@redhat.com>
PR c/58346
c-family/
* c-common.c (pointer_to_zero_sized_aggr_p): New function.
* c-common.h: Declare it.
cp/
* typeck.c (pointer_diff): Give an error on arithmetic on pointer to
an empty aggregate.
c/
* c-typeck.c (pointer_diff): Give an error on arithmetic on pointer to
an empty aggregate.
testsuite/
* c-c++-common/pr58346.c: New test.
--- gcc/c-family/c-common.h.mp 2014-01-13 19:02:22.249870601 +0100
+++ gcc/c-family/c-common.h 2014-01-13 19:04:15.068294390 +0100
@@ -789,6 +789,7 @@ extern bool keyword_is_storage_class_spe
extern bool keyword_is_type_qualifier (enum rid);
extern bool keyword_is_decl_specifier (enum rid);
extern bool cxx_fundamental_alignment_p (unsigned);
+extern bool pointer_to_zero_sized_aggr_p (tree);
#define c_sizeof(LOC, T) c_sizeof_or_alignof_type (LOC, T, true, false, 1)
#define c_alignof(LOC, T) c_sizeof_or_alignof_type (LOC, T, false, false, 1)
--- gcc/c-family/c-common.c.mp 2014-01-13 19:01:20.503637616 +0100
+++ gcc/c-family/c-common.c 2014-01-13 19:42:32.805135382 +0100
@@ -11829,4 +11829,17 @@ cxx_fundamental_alignment_p (unsigned a
TYPE_ALIGN (long_double_type_node)));
}
+/* Return true if T is a pointer to a zero-sized struct/union. */
+
+bool
+pointer_to_zero_sized_aggr_p (tree t)
+{
+ t = strip_pointer_operator (t);
+ if (RECORD_OR_UNION_TYPE_P (t)
+ && TYPE_SIZE (t)
+ && integer_zerop (TYPE_SIZE (t)))
+ return true;
+ return false;
+}
+
#include "gt-c-family-c-common.h"
--- gcc/cp/typeck.c.mp 2014-01-13 19:08:12.237244663 +0100
+++ gcc/cp/typeck.c 2014-01-13 19:10:23.350742070 +0100
@@ -5043,6 +5043,14 @@ pointer_diff (tree op0, tree op1, tree p
return error_mark_node;
}
+ if (pointer_to_zero_sized_aggr_p (TREE_TYPE (op1)))
+ {
+ if (complain & tf_error)
+ error ("arithmetic on pointer to an empty aggregate");
+ else
+ return error_mark_node;
+ }
+
op1 = (TYPE_PTROB_P (ptrtype)
? size_in_bytes (target_type)
: integer_one_node);
--- gcc/c/c-typeck.c.mp 2014-01-13 15:47:01.316105676 +0100
+++ gcc/c/c-typeck.c 2014-01-13 19:58:19.237271626 +0100
@@ -3536,6 +3536,9 @@ pointer_diff (location_t loc, tree op0,
/* This generates an error if op0 is pointer to incomplete type. */
op1 = c_size_in_bytes (target_type);
+ if (pointer_to_zero_sized_aggr_p (TREE_TYPE (orig_op1)))
+ error_at (loc, "arithmetic on pointer to an empty aggregate");
+
/* Divide by the size, in easiest possible way. */
result = fold_build2_loc (loc, EXACT_DIV_EXPR, inttype,
op0, convert (inttype, op1));
--- gcc/testsuite/c-c++-common/pr58346.c.mp 2014-01-13 15:48:20.011420141
+0100
+++ gcc/testsuite/c-c++-common/pr58346.c 2014-01-13 20:25:17.544582444
+0100
@@ -0,0 +1,24 @@
+/* PR c/58346 */
+/* { dg-do compile } */
+
+struct U {
+#ifdef __cplusplus
+ char a[0];
+#endif
+};
+static struct U b[6];
+static struct U **u1, **u2;
+
+int
+foo (struct U *p, struct U *q)
+{
+ return q - p; /* { dg-error "arithmetic on pointer to an empty aggregate" }
*/
+}
+
+void
+bar (void)
+{
+ __PTRDIFF_TYPE__ d = u1 - u2; /* { dg-error "arithmetic on pointer to an
empty aggregate" } */
+ __asm volatile ("" : "+g" (d));
+ foo (&b[0], &b[4]);
+}
Marek
