[PATCH] sparse: treat function pointers as pointers to const data

[Ard Biesheuvel <ard.biesheuvel@linaro.org>]

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.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 evaluate.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/evaluate.c b/evaluate.c
index 66556150ddac..6428312f3e61 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -794,6 +794,14 @@ static unsigned long target_qualifiers(struct symbol *type)
 	unsigned long mod = type->ctype.modifiers & MOD_IGN;
 	if (type->ctype.base_type && type->ctype.base_type->type == SYM_ARRAY)
 		mod = 0;
+
+	/*
+	 * Dereferencing a function pointer does not produce an lvalue,
+	 * which means its target is implicitly 'const', and assigning
+	 * a pointer-to-const value to it is ok.
+	 */
+	if (type->ctype.base_type && type->ctype.base_type->type == SYM_FN)
+		mod |= MOD_CONST;
 	return mod;
 }
 
-- 
1.8.3.2