[PATCH 06/13] format-check: add a function to check to type of strings

[Luc Van Oostenryck <luc.vanoostenryck@gmail.com>]

This checking is currently done by check_assignment_types()
but this is not adequate, for example because it allows
a void pointer for the string argument while a warning
should be issued.

So, add a custom checking function.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 verify-format.c | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/verify-format.c b/verify-format.c
index 0ef2cb863ae9..90fe0ede0431 100644
--- a/verify-format.c
+++ b/verify-format.c
@@ -106,12 +106,44 @@ static int printf_fmt_numtype(struct format_type *fmt,
 	return check_assignment_types(fmt->type, expr, typediff);
 }
 
+// For 's' & 'S' specifiers
+static const char *check_printf_string(struct format_type *fmt, struct symbol *source)
+{
+	const char *typediff = "different base types";
+	struct symbol *target = fmt->type;
+
+	examine_pointer_target(target);
+	examine_pointer_target(source);
+
+	if (type_class(source, &source) != CLASS_PTR)
+		return typediff;
+	if (source->ctype.as)
+		return "different address spaces";
+
+	// get the base type
+	type_class(source->ctype.base_type, &source);
+	type_class(source, &source);
+
+	if (target == &const_string_ctype) {
+		if (source == &char_ctype)
+			return NULL;
+		if (source == &uchar_ctype)
+			return NULL;
+		if (source == &schar_ctype)
+			return NULL;
+	} if (target == &const_wstring_ctype) {
+		if (source == wchar_ctype)
+			return NULL;
+	}
+	return typediff;
+}
+
 static int printf_fmt_string(struct format_type *fmt,
 			     struct expression **expr,
 			     struct symbol *ctype,
 			     const char **typediff)
 {
-	return check_assignment_types(fmt->type, expr, typediff);
+	return !(*typediff = check_printf_string(fmt, ctype));
 }
 
 static int printf_fmt_pointer(struct format_type *fmt,
-- 
2.28.0