Casts to union type are a GCC extension and are similar to
compound literals.
However, sparse doesn't know about them and treats them like
other casts to non-scalars.
So, teach sparse about them, convert them to the corresponding
compound literal and add a warning flag to enable/disable the
associated warning: -W[no-]union-cast.
Note: a difference between union casts and compound literals
is that the union casts yield rvalues while compound
literals are lvalues but this distinction is not yet done
in this series.
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
---
Documentation/release-notes/v0.6.3.rst | 5 +++
evaluate.c | 47 +++++++++++++++++++++++++-
options.c | 2 ++
options.h | 1 +
sparse.1 | 6 ++++
validation/eval/union-cast-no.c | 1 -
validation/eval/union-cast.c | 1 -
7 files changed, 60 insertions(+), 3 deletions(-)
diff --git a/Documentation/release-notes/v0.6.3.rst b/Documentation/release-notes/v0.6.3.rst
new file mode 100644
index 000000000000..1aae742e42de
--- /dev/null
+++ b/Documentation/release-notes/v0.6.3.rst
@@ -0,0 +1,5 @@
+v0.6.3 (2020-xx-xy)
+===================
+
+* Changes in warnings:
+ "warning: cast to union type" [disable with -Wno-union-cast]
diff --git a/evaluate.c b/evaluate.c
index 0563be939f23..847137250d05 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -2948,6 +2948,26 @@ static int cast_flags(struct expression *expr, struct expression *old)
return flags;
}
+///
+// check if a type matches one of the members of a union type
+// @utype: the union type
+// @type: to type to check
+// @return: to identifier of the matching type in the union.
+static struct symbol *find_member_type(struct symbol *utype, struct symbol *type)
+{
+ struct symbol *t, *member;
+
+ if (utype->type != SYM_UNION)
+ return NULL;
+
+ FOR_EACH_PTR(utype->symbol_list, member) {
+ classify_type(member, &t);
+ if (type == t)
+ return member;
+ } END_FOR_EACH_PTR(member);
+ return NULL;
+}
+
static struct symbol *evaluate_compound_literal(struct expression *expr, struct expression *source)
{
struct expression *addr = alloc_expression(expr->pos, EXPR_SYMBOL);
@@ -2973,6 +2993,7 @@ static struct symbol *evaluate_cast(struct expression *expr)
struct expression *source = expr->cast_expression;
struct symbol *ctype;
struct symbol *ttype, *stype;
+ struct symbol *member;
int tclass, sclass;
struct ident *tas = NULL, *sas = NULL;
@@ -3022,8 +3043,32 @@ static struct symbol *evaluate_cast(struct expression *expr)
if (expr->type == EXPR_FORCE_CAST)
goto out;
- if (tclass & (TYPE_COMPOUND | TYPE_FN))
+ if (tclass & (TYPE_COMPOUND | TYPE_FN)) {
+ /*
+ * Special case: cast to union type (GCC extension)
+ * The effect is similar to a compound literal except
+ * that the result is a rvalue.
+ */
+ if ((member = find_member_type(ttype, stype))) {
+ struct expression *item, *init;
+
+ if (Wunion_cast)
+ warning(expr->pos, "cast to union type");
+
+ item = alloc_expression(source->pos, EXPR_IDENTIFIER);
+ item->expr_ident = member->ident;
+ item->ident_expression = source;
+
+ init = alloc_expression(source->pos, EXPR_INITIALIZER);
+ add_expression(&init->expr_list, item);
+
+ // FIXME: this should be a rvalue
+ evaluate_compound_literal(expr, init);
+ return ctype;
+ }
+
warning(expr->pos, "cast to non-scalar");
+ }
if (sclass & TYPE_COMPOUND)
warning(expr->pos, "cast from non-scalar");
diff --git a/options.c b/options.c
index f7e81b84d749..b25f715042f8 100644
--- a/options.c
+++ b/options.c
@@ -129,6 +129,7 @@ int Wtransparent_union = 0;
int Wtypesign = 0;
int Wundef = 0;
int Wuninitialized = 1;
+int Wunion_cast = 0;
int Wuniversal_initializer = 0;
int Wunknown_attribute = 0;
int Wvla = 1;
@@ -866,6 +867,7 @@ static const struct flag warnings[] = {
{ "typesign", &Wtypesign },
{ "undef", &Wundef },
{ "uninitialized", &Wuninitialized },
+ { "union-cast", &Wunion_cast },
{ "universal-initializer", &Wuniversal_initializer },
{ "unknown-attribute", &Wunknown_attribute },
{ "vla", &Wvla },
diff --git a/options.h b/options.h
index 070c0dd87183..40945e287a4a 100644
--- a/options.h
+++ b/options.h
@@ -128,6 +128,7 @@ extern int Wtransparent_union;
extern int Wtypesign;
extern int Wundef;
extern int Wuninitialized;
+extern int Wunion_cast;
extern int Wuniversal_initializer;
extern int Wunknown_attribute;
extern int Wvla;
diff --git a/sparse.1 b/sparse.1
index 60203d5a6463..fecd6dd90d42 100644
--- a/sparse.1
+++ b/sparse.1
@@ -451,6 +451,12 @@ The concerned warnings are, for example, those triggered by
Sparse does not issue these warnings by default, processing '{\ 0\ }'
the same as '{\ }'.
.
+.TP
+.B -Wunion-cast
+Warn on casts to union types.
+
+Sparse does not issues these warnings by default.
+.
.SH MISC OPTIONS
.TP
.B \-\-arch=\fIARCH\fR
diff --git a/validation/eval/union-cast-no.c b/validation/eval/union-cast-no.c
index d06b348d209e..6ba38db8e3f3 100644
--- a/validation/eval/union-cast-no.c
+++ b/validation/eval/union-cast-no.c
@@ -16,7 +16,6 @@ static union u bar(long l)
/*
* check-name: union-cast-no
* check-command: sparse -Wno-union-cast $file
- * check-known-to-fail
*
* check-error-start
eval/union-cast-no.c:13:17: warning: cast to non-scalar
diff --git a/validation/eval/union-cast.c b/validation/eval/union-cast.c
index 1d8167531081..5bee9e0dc705 100644
--- a/validation/eval/union-cast.c
+++ b/validation/eval/union-cast.c
@@ -16,7 +16,6 @@ static union u bar(long a)
/*
* check-name: union-cast
* check-command: sparse -Wunion-cast $file
- * check-known-to-fail
*
* check-error-start
eval/union-cast.c:8:17: warning: cast to union type
--
2.28.0
