[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 defined 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().
(Which were moved there by dcf8e5633e2e6)
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.
include/linux/compiler.h | 8 ++++++++
include/linux/const.h | 8 --------
tools/include/linux/const.h | 8 --------
3 files changed, 8 insertions(+), 16 deletions(-)
Comments
On Mon, Oct 02, 2023 at 02:34:05PM +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 defined 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().
> (Which were moved there by dcf8e5633e2e6)
> 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.
>
> include/linux/compiler.h | 8 ++++++++
> include/linux/const.h | 8 --------
> tools/include/linux/const.h | 8 --------
> 3 files changed, 8 insertions(+), 16 deletions(-)
>
> diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> index d7779a18b24f..2efec9bfcc40 100644
> --- a/include/linux/compiler.h
> +++ b/include/linux/compiler.h
> @@ -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.
> diff --git a/include/linux/const.h b/include/linux/const.h
> index 435ddd72d2c4..81b8aae5a855 100644
> --- a/include/linux/const.h
> +++ b/include/linux/const.h
> @@ -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 */
> diff --git a/tools/include/linux/const.h b/tools/include/linux/const.h
> index 435ddd72d2c4..81b8aae5a855 100644
> --- a/tools/include/linux/const.h
> +++ b/tools/include/linux/const.h
> @@ -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)))
Doesn't tools/ still need its own copy somewhere?
-Kees
> -
> #endif /* _LINUX_CONST_H */
> --
> 2.17.1
>
> -
> Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
> Registration No: 1397386 (Wales)
>
From: Kees Cook
> Sent: 02 October 2023 17:48
>
> On Mon, Oct 02, 2023 at 02:34:05PM +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 defined 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().
> > (Which were moved there by dcf8e5633e2e6)
> > This may not be a good long-term home, but the three definitions
> > belong together.
> >
...
> > diff --git a/tools/include/linux/const.h b/tools/include/linux/const.h
> > index 435ddd72d2c4..81b8aae5a855 100644
> > --- a/tools/include/linux/const.h
> > +++ b/tools/include/linux/const.h
> > @@ -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)))
>
> Doesn't tools/ still need its own copy somewhere?
Nothing failed to build with it removed...
I think I decided that tools actually used compiler.h.
There weren't extra definitions of is_signed_type().
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 */
@@ -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 */