This patch adds a warning (enabled by default) to warn about accessing elements
of atomic structures or unions, which is undefined behavior according to the C
standard. I didn't make this a translation-time error because it's unclear if
it should be so.
Bootstrapped/regtested on x86_64-linux and powerpc64le-linux, ok for trunk?
2015-12-22 Marek Polacek <pola...@redhat.com>
PR c/69002
* c-typeck.c (build_component_ref): Warn when acessing elements of
atomic structures or unions.
* gcc.dg/c11-atomic-1.c: Add dg-warnings.
* gcc.dg/c11-atomic-4.c: New test.
diff --git gcc/c/c-typeck.c gcc/c/c-typeck.c
index a97774f..928fcd5 100644
--- gcc/c/c-typeck.c
+++ gcc/c/c-typeck.c
@@ -2349,6 +2349,18 @@ build_component_ref (location_t loc, tree datum, tree
component)
return error_mark_node;
}
+ /* Accessing elements of atomic structures or unions is undefined
+ behavior (C11 6.5.2.3#5). */
+ if (TYPE_ATOMIC (type) && c_inhibit_evaluation_warnings == 0)
+ {
+ if (code == RECORD_TYPE)
+ warning_at (loc, 0, "accessing a member %qE of an atomic "
+ "structure %qE", component, datum);
+ else
+ warning_at (loc, 0, "accessing a member %qE of an atomic "
+ "union %qE", component, datum);
+ }
+
/* Chain the COMPONENT_REFs if necessary down to the FIELD.
This might be better solved in future the way the C++ front
end does it - by giving the anonymous entities each a
diff --git gcc/testsuite/gcc.dg/c11-atomic-1.c
gcc/testsuite/gcc.dg/c11-atomic-1.c
index c7f9a1e..9702a10 100644
--- gcc/testsuite/gcc.dg/c11-atomic-1.c
+++ gcc/testsuite/gcc.dg/c11-atomic-1.c
@@ -61,15 +61,15 @@ func (_Atomic volatile long al1)
accessing elements of atomic structures and unions is at
translation or execution time; presume here that it's at
execution time. */
- t1.i = at1.i;
- at1.i = t1.i;
- atp1->i = t1.i;
+ t1.i = at1.i; /* { dg-warning "accessing a member .i. of an atomic
structure" } */
+ at1.i = t1.i; /* { dg-warning "accessing a member .i. of an atomic
structure" } */
+ atp1->i = t1.i; /* { dg-warning "accessing a member .i. of an atomic
structure" } */
au1 = u1;
u1 = au1;
av1 = v1;
v1 = av1;
- v1.i = av1.i;
- av1.i = v1.i;
+ v1.i = av1.i; /* { dg-warning "accessing a member .i. of an atomic union" }
*/
+ av1.i = v1.i; /* { dg-warning "accessing a member .i. of an atomic union" }
*/
/* _Atomic is valid on register variables, even if not particularly
useful. */
register _Atomic volatile int ra1 = 1, ra2 = 2;
diff --git gcc/testsuite/gcc.dg/c11-atomic-4.c
gcc/testsuite/gcc.dg/c11-atomic-4.c
index e69de29..81003aa 100644
--- gcc/testsuite/gcc.dg/c11-atomic-4.c
+++ gcc/testsuite/gcc.dg/c11-atomic-4.c
@@ -0,0 +1,92 @@
+/* PR c/69002 */
+/* Test we diagnose accessing elements of atomic structures or unions,
+ which is undefined behavior (C11 6.5.2.3#5). */
+/* { dg-do compile } */
+/* { dg-options "-std=c11 -pedantic-errors" } */
+
+struct S { int x; };
+union U { int x; };
+
+int
+fn1 (_Atomic struct S p)
+{
+ int e = 0 && p.x;
+ return p.x + e; /* { dg-warning "accessing a member .x. of an atomic
structure" } */
+}
+
+int
+fn2 (_Atomic struct S *p)
+{
+ int e = 1 || p->x;
+ return p->x + e; /* { dg-warning "accessing a member .x. of an atomic
structure" } */
+}
+
+void
+fn3 (_Atomic struct S p, int x)
+{
+ p.x = x; /* { dg-warning "accessing a member .x. of an atomic structure" } */
+}
+
+void
+fn4 (_Atomic struct S *p, int x)
+{
+ p->x = x; /* { dg-warning "accessing a member .x. of an atomic structure" }
*/
+}
+
+int
+fn5 (_Atomic struct S p)
+{
+ /* This is OK: Members can be safely accessed using a non-atomic
+ object which is assigned to or from the atomic object. */
+ struct S s = p;
+ return s.x;
+}
+
+int
+fn6 (_Atomic struct S *p)
+{
+ struct S s = *p;
+ return s.x;
+}
+
+int
+fn7 (_Atomic union U p)
+{
+ int e = 0 && p.x;
+ return p.x + e; /* { dg-warning "accessing a member .x. of an atomic union"
} */
+}
+
+int
+fn8 (_Atomic union U *p)
+{
+ int e = 1 || p->x;
+ return p->x + e; /* { dg-warning "accessing a member .x. of an atomic union"
} */
+}
+
+void
+fn9 (_Atomic union U p, int x)
+{
+ p.x = x; /* { dg-warning "accessing a member .x. of an atomic union" } */
+}
+
+void
+fn10 (_Atomic union U *p, int x)
+{
+ p->x = x; /* { dg-warning "accessing a member .x. of an atomic union" } */
+}
+
+int
+fn11 (_Atomic union U p)
+{
+ /* This is OK: Members can be safely accessed using a non-atomic
+ object which is assigned to or from the atomic object. */
+ union U s = p;
+ return s.x;
+}
+
+int
+fn12 (_Atomic union U *p)
+{
+ union U s = *p;
+ return s.x;
+}
Marek
