[v2,next] compiler.h: Move __is_constexpr() to compiler.h.
Commit Message
Prior to f747e6667ebb2 __is_constexpr() was in its only user minmax.h.
That commit moved it to const.h - but that file just defines ULL(x) and
UL(x) so that constants can be defined for .S and .c files.
So apart from the word 'const' it wasn't really a good location.
Instead move the definition to compiler.h just before the similar
is_signed_type() and is_unsigned_type().
This may not be a good long-term home, but the three definitions
belong together.
Signed-off-by: David Laight <david.laight@aculab.com>
---
This makes it possible to use __is_constexpr() inside is_signed_type()
so that the result is constant integer expression for pointer types.
In particular (void *)1 isn't constant enough.
v2: Add a copy into tools/linux/compiler.h to fix perf build.
include/linux/compiler.h | 8 ++++++++
include/linux/const.h | 8 --------
tools/include/linux/compiler.h | 8 ++++++++
tools/include/linux/const.h | 8 --------
4 files changed, 16 insertions(+), 16 deletions(-)
Comments
On Thu, Oct 05, 2023 at 11:39:54AM +0000, David Laight wrote:
> Prior to f747e6667ebb2 __is_constexpr() was in its only user minmax.h.
> That commit moved it to const.h - but that file just defines ULL(x) and
> UL(x) so that constants can be defined for .S and .c files.
> So apart from the word 'const' it wasn't really a good location.
> Instead move the definition to compiler.h just before the similar
> is_signed_type() and is_unsigned_type().
> This may not be a good long-term home, but the three definitions
> belong together.
>
> Signed-off-by: David Laight <david.laight@aculab.com>
Yeah, this is what I'd expect (a duplicate move in tools/). Thanks!
Reviewed-by: Kees Cook <keescook@chromium.org>
From: Kees Cook
> Sent: 05 October 2023 17:22
>
> On Thu, Oct 05, 2023 at 11:39:54AM +0000, David Laight wrote:
> > Prior to f747e6667ebb2 __is_constexpr() was in its only user minmax.h.
> > That commit moved it to const.h - but that file just defines ULL(x) and
> > UL(x) so that constants can be defined for .S and .c files.
> > So apart from the word 'const' it wasn't really a good location.
> > Instead move the definition to compiler.h just before the similar
> > is_signed_type() and is_unsigned_type().
> > This may not be a good long-term home, but the three definitions
> > belong together.
> >
> > Signed-off-by: David Laight <david.laight@aculab.com>
>
> Yeah, this is what I'd expect (a duplicate move in tools/). Thanks!
I did try to run something that might have built 'perf'.
But it complained about a lot of stuff not being installed.
I do wonder if a better home for all these is_xxx() and __is_xxx()
would be at the top of build_bug.h.
While they can be used on their own (eg with __builtin_choose_expr())
they are typically used with the compile-time asserts
(or at least with code that is also doing asserts.)
So there might only be a few places that need the extra #include.
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
It can also be defined more portably as:
#define __is_constexpr(x) \
_Generic(0 ? (void *)((long)(x) * 0) : (int *)0, int *: 1, void *: 0)
Which doesn't rely on 'sizeof (void)' being valid.
But that is for another day.
There is also:
#define is_pointer_type(type) __is_constexpr((type)1)
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
@@ -230,6 +230,14 @@ static inline void *offset_to_ptr(const int *off)
/* &a[0] degrades to a pointer: a different type from an array */
#define __must_be_array(a) BUILD_BUG_ON_ZERO(__same_type((a), &(a)[0]))
+/*
+ * This returns a constant expression while determining if an argument is
+ * a constant expression, most importantly without evaluating the argument.
+ * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
+ */
+#define __is_constexpr(x) \
+ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
/*
* Whether 'type' is a signed type or an unsigned type. Supports scalar types,
* bool and also pointer types.
@@ -3,12 +3,4 @@
#include <vdso/const.h>
-/*
- * This returns a constant expression while determining if an argument is
- * a constant expression, most importantly without evaluating the argument.
- * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
- */
-#define __is_constexpr(x) \
- (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
-
#endif /* _LINUX_CONST_H */
@@ -63,6 +63,14 @@
# define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b))
#endif
+/*
+ * This returns a constant expression while determining if an argument is
+ * a constant expression, most importantly without evaluating the argument.
+ * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
+ */
+#define __is_constexpr(x) \
+ (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
+
#ifdef __ANDROID__
/*
* FIXME: Big hammer to get rid of tons of:
@@ -3,12 +3,4 @@
#include <vdso/const.h>
-/*
- * This returns a constant expression while determining if an argument is
- * a constant expression, most importantly without evaluating the argument.
- * Glory to Martin Uecker <Martin.Uecker@med.uni-goettingen.de>
- */
-#define __is_constexpr(x) \
- (sizeof(int) == sizeof(*(8 ? ((void *)((long)(x) * 0l)) : (int *)8)))
-
#endif /* _LINUX_CONST_H */