[PATCH] avoid useless warning for 'bool <- restricted type' conversion

[PATCH] avoid useless warning for 'bool <- restricted type' conversion

[Luc Van Oostenryck]

Conversion to bool is special in C since this conversion
is essentially the result of the comparison with zero.
As such, some operations which are normally unsafe to
do with restricted types, like casting to an unrestricted
type, are in fact safe to do when converting to bool
and issuing a warning in those case is useless, confusing
and causes people to add useless casts in the code in
order to shut up the warning.

Fix this by catching such 'bool <- restricted type' conversion
and avoid such warnings.

CC: Al Viro <viro@zeniv.linux.org.uk>
Originally-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 evaluate.c                        |  6 ++++++
 validation/bool-cast-restricted.c | 25 +++++++++++++++++++++++++
 2 files changed, 31 insertions(+)
 create mode 100644 validation/bool-cast-restricted.c

diff --git a/evaluate.c b/evaluate.c
index 976857915..3dc26fc09 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -1345,6 +1345,12 @@ static int check_assignment_types(struct symbol *target, struct expression **rp,
 				return 1;
 		} else if (!(sclass & TYPE_RESTRICT))
 			goto Cast;
+                if (t == &bool_ctype) {
+                        if (is_fouled_type(s))
+                                warning((*rp)->pos, "%s degrades to integer",
+                                        show_typename(s->ctype.base_type));
+                        goto Cast;
+                }
 		*typediff = "different base types";
 		return 0;
 	}
diff --git a/validation/bool-cast-restricted.c b/validation/bool-cast-restricted.c
new file mode 100644
index 000000000..f6776b050
--- /dev/null
+++ b/validation/bool-cast-restricted.c
@@ -0,0 +1,25 @@
+typedef unsigned   int __attribute__((bitwise)) large_t;
+#define	LBIT	((__attribute__((force)) large_t) 1)
+
+_Bool lfoo(large_t x) { return x; }
+_Bool lbar(large_t x) { return ~x; }
+_Bool lbaz(large_t x) { return !x; }
+_Bool lqux(large_t x) { return x & LBIT; }
+
+
+typedef unsigned short __attribute__((bitwise)) small_t;
+#define	SBIT	((__attribute__((force)) small_t) 1)
+
+_Bool sfoo(small_t x) { return x; }
+_Bool sbar(small_t x) { return ~x; }
+_Bool sbaz(small_t x) { return !x; }
+_Bool squx(small_t x) { return x & SBIT; }
+
+/*
+ * check-name: bool-cast-restricted.c
+ * check-command: sparse -Wno-decl $file
+ *
+ * check-error-start
+bool-cast-restricted.c:14:32: warning: restricted small_t degrades to integer
+ * check-error-end
+ */
-- 
2.12.2

Re: [PATCH] avoid useless warning for 'bool <- restricted type' conversion

[Christopher Li]

On Thu, May 11, 2017 at 9:21 AM, Luc Van Oostenryck
<luc.vanoostenryck@gmail.com> wrote:
> Conversion to bool is special in C since this conversion
> is essentially the result of the comparison with zero.
> As such, some operations which are normally unsafe to
> do with restricted types, like casting to an unrestricted
> type, are in fact safe to do when converting to bool
> and issuing a warning in those case is useless, confusing
> and causes people to add useless casts in the code in
> order to shut up the warning.
>
> Fix this by catching such 'bool <- restricted type' conversion
> and avoid such warnings.

The change seems fine. However, have you run the test-suite
with this change? It seems cause some test do not pass.
I assume it is cause by different error message it will output.

Chris

Re: [PATCH] avoid useless warning for 'bool <- restricted type' conversion

[Luc Van Oostenryck]

On Thu, May 11, 2017 at 9:41 PM, Christopher Li <sparse@chrisli.org> wrote:
> On Thu, May 11, 2017 at 9:21 AM, Luc Van Oostenryck
> <luc.vanoostenryck@gmail.com> wrote:
>> Conversion to bool is special in C since this conversion
>> is essentially the result of the comparison with zero.
>> As such, some operations which are normally unsafe to
>> do with restricted types, like casting to an unrestricted
>> type, are in fact safe to do when converting to bool
>> and issuing a warning in those case is useless, confusing
>> and causes people to add useless casts in the code in
>> order to shut up the warning.
>>
>> Fix this by catching such 'bool <- restricted type' conversion
>> and avoid such warnings.
>
> The change seems fine. However, have you run the test-suite
> with this change? It seems cause some test do not pass.
> I assume it is cause by different error message it will output.

Oh my, sorry.
I *have* run the test-suite but then I've forgotten to commit
the change needed for two test cases.

Thanks for noticing this.

-- Luc

Re: [PATCH] FS: Fixing return type of unsigned_offsets

[Luc Van Oostenryck]

On Thu, May 11, 2017 at 8:07 AM, Al Viro <viro@zeniv.linux.org.uk> wrote:
> FVO"needed" equal to "needed to make sparse STFU"?  If anything, that's
> sparse being wrong - evaluate.c:check_assignment_type() should do
>                 if (t == &ctype_bool) {
>                         if (is_fouled_type(s))
>                                 warning((*rp)->pos, "%s degrades to integer",
>                                         show_typename(s->ctype.base_type));
>                         goto Cast;
>                 }
> right after
>                 } else if (!(sclass & TYPE_RESTRICT))
>                         goto Cast;

What about an explicit cast of restricted types to bool?
I think we would want the equivalent of this patch for those too.

-- Luc

[PATCH] avoid useless warning for 'bool <- restricted type' conversion

[Luc Van Oostenryck]

Conversion to bool is special in C since this conversion
is essentially the result of the comparison with zero.
As such, some operations which are normally unsafe to
do with restricted types, like casting to an unrestricted
type, are in fact safe to do when converting to bool
and issuing a warning in those case is useless, confusing
and causes people to add useless casts in the code in
order to shut up the warning.

Fix this by catching such 'bool <- restricted type' conversion
and avoid such warnings.

CC: Al Viro <viro@zeniv.linux.org.uk>
Originally-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>
---
 evaluate.c                        |  6 ++++++
 validation/bool-cast-bad.c        |  3 ---
 validation/bool-cast-implicit.c   |  3 ---
 validation/bool-cast-restricted.c | 25 +++++++++++++++++++++++++
 4 files changed, 31 insertions(+), 6 deletions(-)
 create mode 100644 validation/bool-cast-restricted.c

diff --git a/evaluate.c b/evaluate.c
index 976857915..3dc26fc09 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -1345,6 +1345,12 @@ static int check_assignment_types(struct symbol *target, struct expression **rp,
 				return 1;
 		} else if (!(sclass & TYPE_RESTRICT))
 			goto Cast;
+                if (t == &bool_ctype) {
+                        if (is_fouled_type(s))
+                                warning((*rp)->pos, "%s degrades to integer",
+                                        show_typename(s->ctype.base_type));
+                        goto Cast;
+                }
 		*typediff = "different base types";
 		return 0;
 	}
diff --git a/validation/bool-cast-bad.c b/validation/bool-cast-bad.c
index b7e7c058d..a0b091e1c 100644
--- a/validation/bool-cast-bad.c
+++ b/validation/bool-cast-bad.c
@@ -15,9 +15,6 @@ static _Bool fstse(struct s a) { return (_Bool)a; }
  * check-command: sparse $file
  *
  * check-error-start
-bool-cast-bad.c:8:41: warning: incorrect type in return expression (different base types)
-bool-cast-bad.c:8:41:    expected bool
-bool-cast-bad.c:8:41:    got restricted le16 [usertype] a
 bool-cast-bad.c:9:42: warning: cast from restricted le16
 bool-cast-bad.c:10:41: warning: incorrect type in return expression (different base types)
 bool-cast-bad.c:10:41:    expected bool
diff --git a/validation/bool-cast-implicit.c b/validation/bool-cast-implicit.c
index ee8b705b9..9d89443b1 100644
--- a/validation/bool-cast-implicit.c
+++ b/validation/bool-cast-implicit.c
@@ -21,8 +21,5 @@ static _Bool fres(le16 a) { return a; }
  * check-output-excludes: cast\\.
  *
  * check-error-start
-bool-cast-implicit.c:15:36: warning: incorrect type in return expression (different base types)
-bool-cast-implicit.c:15:36:    expected bool
-bool-cast-implicit.c:15:36:    got restricted le16 [usertype] a
  * check-error-end
  */
diff --git a/validation/bool-cast-restricted.c b/validation/bool-cast-restricted.c
new file mode 100644
index 000000000..f6776b050
--- /dev/null
+++ b/validation/bool-cast-restricted.c
@@ -0,0 +1,25 @@
+typedef unsigned   int __attribute__((bitwise)) large_t;
+#define	LBIT	((__attribute__((force)) large_t) 1)
+
+_Bool lfoo(large_t x) { return x; }
+_Bool lbar(large_t x) { return ~x; }
+_Bool lbaz(large_t x) { return !x; }
+_Bool lqux(large_t x) { return x & LBIT; }
+
+
+typedef unsigned short __attribute__((bitwise)) small_t;
+#define	SBIT	((__attribute__((force)) small_t) 1)
+
+_Bool sfoo(small_t x) { return x; }
+_Bool sbar(small_t x) { return ~x; }
+_Bool sbaz(small_t x) { return !x; }
+_Bool squx(small_t x) { return x & SBIT; }
+
+/*
+ * check-name: bool-cast-restricted.c
+ * check-command: sparse -Wno-decl $file
+ *
+ * check-error-start
+bool-cast-restricted.c:14:32: warning: restricted small_t degrades to integer
+ * check-error-end
+ */
-- 
2.12.2