Recent changes to the min()/max() macros in include/linux/kernel.h
have added a lot of noise to sparse output; this is due to the
*huge* number of new sizeof(void) warnings, most of which can
largely be ignored.
Add the -Wsizeof_void flag to enable/disable these warnings on
demand; the warning itself has been disabled by default to reduce the
large influx of noise which was inadvertently added by commit
3c8ba0d61d04ced9f8 (kernel.h: Retain constant expression output
for max()/min()).
Update the manpage to document the new flag.
CC: Kees Cook <keescook@xxxxxxxxxxxx>
CC: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
CC: Martin Uecker <Martin.Uecker@xxxxxxxxxxxxxxxxxxxxx>
CC: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
CC: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
CC: Christopher Li <sparse@xxxxxxxxxxx>
Signed-off-by: Joey Pabalinas <joeypabalinas@xxxxxxxxx>
4 files changed, 24 insertions(+), 2 deletions(-)
diff --git a/evaluate.c b/evaluate.c
index b96696d3a51396800a..33e5fcabc4e755e0b7 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -2169,7 +2169,8 @@ static struct symbol *evaluate_sizeof(struct expression *expr)
size = type->bit_size;
if (size < 0 && is_void_type(type)) {
- warning(expr->pos, "expression using sizeof(void)");
+ if (Wsizeof_void)
+ warning(expr->pos, "expression using sizeof(void)");
size = bits_in_char;
}
diff --git a/lib.c b/lib.c
index 645132a892107512a1..35b41ad5becddf6b59 100644
--- a/lib.c
+++ b/lib.c
@@ -245,6 +245,7 @@ int Wptr_subtraction_blows = 0;
int Wreturn_void = 0;
int Wshadow = 0;
int Wsizeof_bool = 0;
+int Wsizeof_void = 0;
int Wtautological_compare = 0;
int Wtransparent_union = 0;
int Wtypesign = 0;
@@ -536,6 +537,7 @@ static const struct warning {
{ "return-void", &Wreturn_void },
{ "shadow", &Wshadow },
{ "sizeof-bool", &Wsizeof_bool },
+ { "sizeof-void", &Wsizeof_void },
{ "sparse-error", &Wsparse_error },
{ "tautological-compare", &Wtautological_compare },
{ "transparent-union", &Wtransparent_union },
diff --git a/lib.h b/lib.h
index a9b70b07686801305c..517f933e97d504f2bb 100644
--- a/lib.h
+++ b/lib.h
@@ -138,6 +138,7 @@ extern int Wptr_subtraction_blows;
extern int Wreturn_void;
extern int Wshadow;
extern int Wsizeof_bool;
+extern int Wsizeof_void;
extern int Wtautological_compare;
extern int Wtransparent_union;
extern int Wtypesign;
diff --git a/sparse.1 b/sparse.1
index e183204de623efd022..09eecf9cbb06b9acc4 100644
--- a/sparse.1
+++ b/sparse.1
@@ -323,7 +323,25 @@ Sparse does not issue these warnings by default.
.B \-Wsizeof-bool
Warn when checking the sizeof a _Bool.
-C99 does not specify the sizeof a _Bool. gcc uses 1.
+C99 does not specify the sizeof a _Bool. GCC uses \fI1\fR.
+
+Sparse does not issue these warnings by default.
+.
+.TP
+.B \-Wsizeof-void
+Warn when checking the sizeof a void.
+
+C99 does not allow the sizeof operator to be applied to incomplete types
+such as void. GCC allows \fBsizeof(void)\fR as an extension and uses \fI1\fR.
+
+Although non-standard, \fBsizeof(void)\fR is often useful when the intent
+is to operate on an expression without evaluating it, e.g. in the following
+integer constant expression predicate:
+
+.nf
+#define __is_constexpr(x) \\
+ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+.fi
Sparse does not issue these warnings by default.
.
--
2.17.0.rc1.35.g90bbd502d54fe92035.dirty
Attachment:
signature.asc
Description: PGP signature
