Recent changes to the min()/max() macros in include/linux/kernel.h
have added a lot of noise when compiling the kernel with Sparse checking
enabled. This mostly is due to the *huge* increase in the number of
sizeof(void) warnings, a larger number of which can safely be ignored.
Add the -Wpointer-arith flag to enable/disable these warnings (along
with the warning when applying sizeof to function types exactly like the
GCC -Wpointer-arith flag) 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: Christopher Li <sparse@xxxxxxxxxxx>
CC: Joey Pabalinas <joeypabalinas@xxxxxxxxx>
CC: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
Signed-off-by: Joey Pabalinas <joeypabalinas@xxxxxxxxx>
Signed-off-by: Luc Van Oostenryck <luc.vanoostenryck@xxxxxxxxx>
4 files changed, 26 insertions(+), 2 deletions(-)
diff --git a/evaluate.c b/evaluate.c
index 4e1dffe9c5416380df..f828da37df8e686623 100644
--- a/evaluate.c
+++ b/evaluate.c
@@ -2193,7 +2193,8 @@ 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 (Wpointer_arith)
+ warning(expr->pos, "expression using sizeof(void)");
size = bits_in_char;
}
@@ -2204,7 +2205,8 @@ static struct symbol *evaluate_sizeof(struct expression *expr)
}
if (is_function(type->ctype.base_type)) {
- warning(expr->pos, "expression using sizeof on a function");
+ if (Wpointer_arith)
+ warning(expr->pos, "expression using sizeof on a function");
size = bits_in_char;
}
diff --git a/lib.c b/lib.c
index 73d372c36626538bab..f7fdac96674aec4c24 100644
--- a/lib.c
+++ b/lib.c
@@ -242,6 +242,7 @@ int Woverride_init = 1;
int Woverride_init_all = 0;
int Woverride_init_whole_range = 0;
int Wparen_string = 0;
+int Wpointer_arith = 0;
int Wptr_subtraction_blows = 0;
int Wreturn_void = 0;
int Wshadow = 0;
@@ -654,6 +655,7 @@ static const struct flag warnings[] = {
{ "return-void", &Wreturn_void },
{ "shadow", &Wshadow },
{ "sizeof-bool", &Wsizeof_bool },
+ { "pointer-arith", &Wpointer_arith },
{ "sparse-error", &Wsparse_error },
{ "tautological-compare", &Wtautological_compare },
{ "transparent-union", &Wtransparent_union },
diff --git a/lib.h b/lib.h
index 3050b5577ba4d42e97..e34bb9a02ebac03f52 100644
--- a/lib.h
+++ b/lib.h
@@ -151,6 +151,7 @@ extern int Woverride_init;
extern int Woverride_init_all;
extern int Woverride_init_whole_range;
extern int Wparen_string;
+extern int Wpointer_arith;
extern int Wptr_subtraction_blows;
extern int Wreturn_void;
extern int Wshadow;
diff --git a/sparse.1 b/sparse.1
index 88343f3170f195297a..4379406999c94b806e 100644
--- a/sparse.1
+++ b/sparse.1
@@ -288,6 +288,25 @@ Standard C syntax does not permit a parenthesized string as an array
initializer. GCC allows this syntax as an extension. With
\fB\-Wparen\-string\fR, Sparse will warn about this syntax.
+Sparse does not issue these warnings by default.
+.
+.TP
+.B \-Wpointer-arith
+Warn about anything that depends on the \fBsizeof\fR a function type or of void.
+
+C99 does not allow the \fBsizeof\fR operator to be applied to function types or to
+incomplete types such as void. GCC allows \fBsizeof\fR to be applied to these
+types as an extension and assigns these types a size of \fI1\fR.
+
+Although non-standard (and somewhat illogical), constructs such as \fBsizeof(void)\fR
+are 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.
.
.TP
--
2.17.0.rc1.35.g90bbd502d54fe92035.dirty
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