[PATCH 10/13] flex-array: warn when using sizeof() on a flexible array

From: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
To: linux-sparse@vger.kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
	Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
Subject: [PATCH 10/13] flex-array: warn when using sizeof() on a flexible array
Date: Thu,  1 Oct 2020 01:18:25 +0200	[thread overview]
Message-ID: <20200930231828.66751-11-luc.vanoostenryck@gmail.com> (raw)
In-Reply-To: <20200930231828.66751-1-luc.vanoostenryck@gmail.com>

Using sizeof() on a structure containing a flexible array
will ignore the 'flexible' part. This is maybe what is expected
but maybe not, so add an option -Wflexible-array-sizeof to
warn on such usage.

Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 evaluate.c                     | 3 +++
 options.c                      | 2 ++
 options.h                      | 1 +
 sparse.1                       | 7 +++++++
 validation/flex-array-sizeof.c | 1 -
 5 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/evaluate.c b/evaluate.c
index c1ef348a475e..cfbb6ada4153 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -2253,6 +2253,9 @@ static struct symbol *evaluate_sizeof(struct expression *expr)
 		size = bits_in_char;
 	}
 
+	if (has_flexible_array(type) && Wflexible_array_sizeof)
+		warning(expr->pos, "using sizeof on a flexible structure");
+
 	if (is_array_type(type) && size < 0) {	// VLA, 1-dimension only
 		struct expression *base, *size;
 		struct symbol *base_type;
diff --git a/options.c b/options.c
index 294dfd3be77a..ce88fbf6ed61 100644
--- a/options.c
+++ b/options.c
@@ -100,6 +100,7 @@ int Wdesignated_init = 1;
 int Wdo_while = 0;
 int Wenum_mismatch = 1;
 int Wexternal_function_has_definition = 1;
+int Wflexible_array_sizeof = 0;
 int Wimplicit_int = 1;
 int Winit_cstring = 0;
 int Wint_to_pointer_cast = 1;
@@ -840,6 +841,7 @@ static const struct flag warnings[] = {
 	{ "do-while", &Wdo_while },
 	{ "enum-mismatch", &Wenum_mismatch },
 	{ "external-function-has-definition", &Wexternal_function_has_definition },
+	{ "flexible-array-sizeof", &Wflexible_array_sizeof },
 	{ "implicit-int", &Wimplicit_int },
 	{ "init-cstring", &Winit_cstring },
 	{ "int-to-pointer-cast", &Wint_to_pointer_cast },
diff --git a/options.h b/options.h
index abdf08645ad2..feb351a36c9e 100644
--- a/options.h
+++ b/options.h
@@ -99,6 +99,7 @@ extern int Wdesignated_init;
 extern int Wdo_while;
 extern int Wenum_mismatch;
 extern int Wexternal_function_has_definition;
+extern int Wflexible_array_sizeof;
 extern int Wimplicit_int;
 extern int Winit_cstring;
 extern int Wint_to_pointer_cast;
diff --git a/sparse.1 b/sparse.1
index 48dab7a9a5c1..5f98df33a231 100644
--- a/sparse.1
+++ b/sparse.1
@@ -257,6 +257,13 @@ Sparse issues these warnings by default.  To turn them off, use
 \fB\-Wno\-external\-function\-has\-definition\fR.
 .
 .TP
+.B -Wflexible-array-sizeof
+Warn about using the sizeof operator on a structure containing a flexible array,
+possibly recursively.
+
+Sparse does not issue these warnings by default.
+.
+.TP
 .B \-Winit\-cstring
 Warn about initialization of a char array with a too long constant C string.
 
diff --git a/validation/flex-array-sizeof.c b/validation/flex-array-sizeof.c
index 3359509d0084..05394e19a6b2 100644
--- a/validation/flex-array-sizeof.c
+++ b/validation/flex-array-sizeof.c
@@ -11,7 +11,6 @@ static int foo(struct s *s)
 /*
  * check-name: flex-array-sizeof
  * check-command: sparse -Wflexible-array-sizeof $file
- * check-known-to-fail
  *
  * check-error-start
 flex-array-sizeof.c:8:16: warning: using sizeof on a flexible structure
-- 
2.28.0

