GCC accepts attribute format even on functions without a prototype.
However, when such a function is subsequently redeclared with
a prototype the attribute validation runs into trouble. To avoid
the ICE I considered a) dropping the attribute on functions declared
without a prototype (like Clang does) and b) dropping the attribute
only when the function is subsequently redeclared with a prototype.
Since (b) is slightly safer in terms of retaining potentially useful
functionality the attached patch implements it and verifies that
the attribute is still accepted on functions without a prototype
and has the expected effect.
Tested on x86_64-linux. I propose this for both GCC 10 and 9.
Martin
PS The solution causes a redunant warning for each instance of
a redeclaration with a prototype of a function without a prototype
but with attribute format. Since this seems like a rare problem
I don't think it's worth going to the trouble of making sure only
one warning.
PPS I don't think it's intentional that GCC accepts attribute format
on functions without a prototype, first because it normally requires
that the format argument be a char*, and second because I could find
no tests for the "feature" in the test suite. It would make sense
to me reject such declarations but I don't think now is a good time
for such a change.
PR c/93812 - ICE on redeclaration of an attribute format function without protoype
gcc/c/ChangeLog:
PR c/93812
* c-typeck.c (build_functype_attribute_variant): New function.
(composite_type): Call it.
gcc/testsuite/ChangeLog:
PR c/93812
* gcc.dg/format/proto.c: New test.
diff --git a/gcc/c/c-typeck.c b/gcc/c/c-typeck.c
index 8df0849bd8b..308fcffcfb0 100644
--- a/gcc/c/c-typeck.c
+++ b/gcc/c/c-typeck.c
@@ -353,7 +353,28 @@ c_vla_type_p (const_tree t)
return true;
return false;
}
-
+
+/* If NTYPE is a type of a non-variadic function with a prototype
+ and OTYPE is a type of a function without a prototype and ATTRS
+ contains attribute format, diagnosess and removes it from ATTRS.
+ Returns the result of build_type_attribute_variant of NTYPE and
+ the (possibly) modified ATTRS. */
+
+static tree
+build_functype_attribute_variant (tree ntype, tree otype, tree attrs)
+{
+ if (!prototype_p (otype)
+ && prototype_p (ntype)
+ && lookup_attribute ("format", attrs))
+ {
+ warning_at (input_location, OPT_Wattributes,
+ "%qs attribute cannot be applied to a function that "
+ "does not take variable arguments", "format");
+ attrs = remove_attribute ("format", attrs);
+ }
+ return build_type_attribute_variant (ntype, attrs);
+
+}
/* Return the composite type of two compatible types.
We assume that comptypes has already been done and returned
@@ -504,9 +525,9 @@ composite_type (tree t1, tree t2)
/* Save space: see if the result is identical to one of the args. */
if (valtype == TREE_TYPE (t1) && !TYPE_ARG_TYPES (t2))
- return build_type_attribute_variant (t1, attributes);
+ return build_functype_attribute_variant (t1, t2, attributes);
if (valtype == TREE_TYPE (t2) && !TYPE_ARG_TYPES (t1))
- return build_type_attribute_variant (t2, attributes);
+ return build_functype_attribute_variant (t2, t1, attributes);
/* Simple way if one arg fails to specify argument types. */
if (TYPE_ARG_TYPES (t1) == NULL_TREE)
diff --git a/gcc/testsuite/gcc.dg/format/proto.c b/gcc/testsuite/gcc.dg/format/proto.c
new file mode 100644
index 00000000000..b2050c9de5b
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/format/proto.c
@@ -0,0 +1,89 @@
+/* PR c/93812 - ICE on redeclaration of an attribute format function without
+ protoype
+ It's not clear that attribute format should be accepted on functions
+ without a prototype. If it's decided that it shouldn't be the tests
+ here will need to be adjusted.
+ { dg-do compile }
+ { dg-options "-Wall" } */
+
+#define FMT(n1, n2) __attribute__((__format__(__printf__, n1, n2)))
+
+// Exercise function declarations.
+FMT (1, 2) void print1 ();
+
+FMT (2, 3) void print2 ();
+ void print2 ();
+
+FMT (3, 4) void print3 ();
+FMT (3, 4) void print3 ();
+
+FMT (1, 2) void print4 ();
+ void print4 (void); // { dg-warning "'format' attribute cannot be applied to a function that does not take variable arguments" }
+
+ void print5 ();
+FMT (1, 2) void print5 (void); // { dg-warning "\\\[-Wattributes" }
+
+FMT (1, 2) void print6 ();
+ void print6 (const char*, ...); // { dg-error "conflicting types" }
+
+ void print7 (const char*, ...);
+FMT (1, 2) void print7 (); // { dg-error "conflicting types" }
+
+
+// Exercise function calls.
+void test_print (void)
+{
+ print1 ("%i %s", 123, "");
+ print1 ("%s %i", 123, 123); // { dg-warning "\\\[-Wformat" }
+
+ print2 (0, "%s %i", "", 123);
+ print2 (1, "%i %s", "", 123); // { dg-warning "\\\[-Wformat" }
+
+ print3 (0, 1, "%s %i", "", 123);
+ print3 (1, 2, "%i %s", "", 123); // { dg-warning "\\\[-Wformat" }
+
+ // Just verify there's no ICE.
+ print4 ();
+ print5 ();
+ print6 ("%i %s", 123, "");
+}
+
+
+// Exercise declarations of pointers to functions.
+FMT (1, 2) void (*pfprint1)();
+
+FMT (2, 3) void (*pfprint2)();
+ void (*pfprint2)();
+
+FMT (3, 4) void (*pfprint3)();
+FMT (3, 4) void (*pfprint3)();
+
+FMT (1, 2) void (*pfprint4)();
+ void (*pfprint4)(void); // { dg-warning "'format' attribute cannot be applied to a function that does not take variable arguments" }
+
+ void (*pfprint5)();
+FMT (1, 2) void (*pfprint5)(void); // { dg-warning "\\\[-Wattributes" }
+
+FMT (1, 2) void (*pfprint6)();
+ void (*pfprint6)(const char*, ...); // { dg-error "conflicting types" }
+
+ void (*pfprint7)(const char*, ...);
+FMT (1, 2) void (*pfprint7)(); // { dg-error "conflicting types" }
+
+// Exercise calls via function pointers.
+void test_pfprint (void)
+{
+ pfprint1 ("%i %s", 123, "");
+ pfprint1 ("%s %i", 123, 123); // { dg-warning "\\\[-Wformat" }
+
+ pfprint2 (0, "%s %i", "", 123);
+ pfprint2 (1, "%i %s", "", 123); // { dg-warning "\\\[-Wformat" }
+
+ pfprint3 (0, 1, "%s %i", "", 123);
+ pfprint3 (1, 2, "%i %s", "", 123); // { dg-warning "\\\[-Wformat" }
+
+ // Just verify there's no ICE.
+ pfprint4 ();
+ pfprint5 ();
+ pfprint6 ("%i %s", 123, "");
+}
