This code snippet:
static void bar(void const *arg)
{
int (*foo)(void) = arg;
}
produces the following warning:
test.c:4:28: warning: incorrect type in initializer (different modifiers)
test.c:4:28: expected int ( *foo )( ... )
test.c:4:28: got void const *arg
which is caused by the fact that the function pointer 'foo' is not annotated
as being a pointer to const data. However, dereferencing a function pointer
does not produce an lvalue, so a function pointer points to const data by
definition, and we should treat it accordingly.
To avoid producing a warning on the inverse case, i.e.,
static void bar(void)
{
void *foo = bar;
}
we only address the case where the function pointer is the target of
an assignment.
Reviewed-by: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
---
v3: add rationale for restriction to assignments to commit message
add R-b
v2: only treat function pointers as pointers to const data when they are the
target of an assignment
evaluate.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/evaluate.c b/evaluate.c
index 66556150ddac..a5a830978bda 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -1359,6 +1359,15 @@ static int compatible_assignment_types(struct expression *expr, struct symbol *t
typediff = "different address spaces";
goto Err;
}
+ /*
+ * If this is a function pointer assignment, it is
+ * actually fine to assign a pointer to const data to
+ * it, as a function pointer points to const data
+ * implicitly, i.e., dereferencing it does not produce
+ * an lvalue.
+ */
+ if (b1->type == SYM_FN)
+ mod1 |= MOD_CONST;
if (mod2 & ~mod1) {
typediff = "different modifiers";
goto Err;
--
1.8.3.2
--
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