mult_frac() evaluates _all_ arguments multiple times in the body.
Clarify comment while I'm at it.
Signed-off-by: Alexey Dobriyan <[email protected]>
---
include/linux/math.h | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
--- a/include/linux/math.h
+++ b/include/linux/math.h
@@ -118,17 +118,17 @@ __STRUCT_FRACT(s32)
__STRUCT_FRACT(u32)
#undef __STRUCT_FRACT
-/*
- * Multiplies an integer by a fraction, while avoiding unnecessary
- * overflow or loss of precision.
- */
-#define mult_frac(x, numer, denom)( \
-{ \
- typeof(x) quot = (x) / (denom); \
- typeof(x) rem = (x) % (denom); \
- (quot * (numer)) + ((rem * (numer)) / (denom)); \
-} \
-)
+/* Calculate "x * n / d" without unnecessary overflow or loss of precision. */
+#define mult_frac(x, n, d) \
+({ \
+ typeof(x) x_ = (x); \
+ typeof(n) n_ = (n); \
+ typeof(d) d_ = (d); \
+ \
+ typeof(x) q = x_ / d_; \
+ typeof(x) r = x_ % d_; \
+ q * n_ + r * n_ / d_; \
+})
#define sector_div(a, b) do_div(a, b)
On Fri, 19 May 2023 23:24:54 +0300 Alexey Dobriyan <[email protected]> wrote:
> mult_frac() evaluates _all_ arguments multiple times in the body.
>
> --- a/include/linux/math.h
> +++ b/include/linux/math.h
> @@ -118,17 +118,17 @@ __STRUCT_FRACT(s32)
> __STRUCT_FRACT(u32)
> #undef __STRUCT_FRACT
>
> -/*
> - * Multiplies an integer by a fraction, while avoiding unnecessary
> - * overflow or loss of precision.
> - */
> -#define mult_frac(x, numer, denom)( \
> -{ \
> - typeof(x) quot = (x) / (denom); \
> - typeof(x) rem = (x) % (denom); \
> - (quot * (numer)) + ((rem * (numer)) / (denom)); \
> -} \
> -)
> +/* Calculate "x * n / d" without unnecessary overflow or loss of precision. */
> +#define mult_frac(x, n, d) \
> +({ \
> + typeof(x) x_ = (x); \
> + typeof(n) n_ = (n); \
> + typeof(d) d_ = (d); \
> + \
> + typeof(x) q = x_ / d_; \
> + typeof(x) r = x_ % d_; \
> + q * n_ + r * n_ / d_; \
> +})
>
I like, but the compiler doesn't. x86_64 allmodconfig, gcc-12.2.0.
In file included from ./include/linux/math64.h:6,
from ./include/linux/time.h:6,
from ./include/linux/ktime.h:24,
from ./include/linux/timer.h:6,
from drivers/target/target_core_iblock.c:16:
drivers/target/target_core_iblock.c: In function 'iblock_configure_device':
drivers/target/target_core_iblock.c:127:73: error: passing argument 1 of 'queue_max_hw_sectors' makes pointer from integer without a cast [-Werror=int-conversion]
127 | dev->dev_attrib.hw_max_sectors = mult_frac(queue_max_hw_sectors(q),
| ^
| |
| unsigned int
./include/linux/math.h:129:16: note: in definition of macro 'mult_frac'
129 | typeof(x) r = x_ % d_; \
| ^
In file included from drivers/target/target_core_iblock.c:18:
./include/linux/blkdev.h:1112:77: note: expected 'const struct request_queue *' but argument is of type 'unsigned int'
1112 | static inline unsigned int queue_max_hw_sectors(const struct request_queue *q)
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
cc1: all warnings being treated as errors
make[3]: *** [scripts/Makefile.build:252: drivers/target/target_core_iblock.o] Error 1
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [scripts/Makefile.build:494: drivers/target] Error 2
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [scripts/Makefile.build:494: drivers] Error 2
make: *** [Makefile:2026: .] Error 2
On Fri, May 19, 2023 at 03:36:22PM -0700, Andrew Morton wrote:
> On Fri, 19 May 2023 23:24:54 +0300 Alexey Dobriyan <[email protected]> wrote:
>
> > mult_frac() evaluates _all_ arguments multiple times in the body.
> >
> > --- a/include/linux/math.h
> > +++ b/include/linux/math.h
> > @@ -118,17 +118,17 @@ __STRUCT_FRACT(s32)
> > __STRUCT_FRACT(u32)
> > #undef __STRUCT_FRACT
> >
> > -/*
> > - * Multiplies an integer by a fraction, while avoiding unnecessary
> > - * overflow or loss of precision.
> > - */
> > -#define mult_frac(x, numer, denom)( \
> > -{ \
> > - typeof(x) quot = (x) / (denom); \
> > - typeof(x) rem = (x) % (denom); \
> > - (quot * (numer)) + ((rem * (numer)) / (denom)); \
> > -} \
> > -)
> > +/* Calculate "x * n / d" without unnecessary overflow or loss of precision. */
> > +#define mult_frac(x, n, d) \
> > +({ \
> > + typeof(x) x_ = (x); \
> > + typeof(n) n_ = (n); \
> > + typeof(d) d_ = (d); \
> > + \
> > + typeof(x) q = x_ / d_; \
> > + typeof(x) r = x_ % d_; \
> > + q * n_ + r * n_ / d_; \
> > +})
> >
>
> I like, but the compiler doesn't. x86_64 allmodconfig, gcc-12.2.0.
>
> In file included from ./include/linux/math64.h:6,
> from ./include/linux/time.h:6,
> from ./include/linux/ktime.h:24,
> from ./include/linux/timer.h:6,
> from drivers/target/target_core_iblock.c:16:
> drivers/target/target_core_iblock.c: In function 'iblock_configure_device':
> drivers/target/target_core_iblock.c:127:73: error: passing argument 1 of 'queue_max_hw_sectors' makes pointer from integer without a cast [-Werror=int-conversion]
> 127 | dev->dev_attrib.hw_max_sectors = mult_frac(queue_max_hw_sectors(q),
> | ^
> | |
> | unsigned int
> ./include/linux/math.h:129:16: note: in definition of macro 'mult_frac'
> 129 | typeof(x) r = x_ % d_; \
> | ^
> In file included from drivers/target/target_core_iblock.c:18:
> ./include/linux/blkdev.h:1112:77: note: expected 'const struct request_queue *' but argument is of type 'unsigned int'
> 1112 | static inline unsigned int queue_max_hw_sectors(const struct request_queue *q)
> | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
In my defence, original macro has the same bug:
#define M(a) \
({ \
typeof(a) b = ...; \
typeof(a) c = ...; \
Now, first typeof can use f(b) because second b doesn't exist yet.
But second typeof can not because second b already exists with potentially
incompatible type.
mult_frac() evaluates _all_ arguments multiple times in the body.
Clarify comment while I'm at it.
Signed-off-by: Alexey Dobriyan <[email protected]>
---
include/linux/math.h | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)
--- a/include/linux/math.h
+++ b/include/linux/math.h
@@ -118,17 +118,17 @@ __STRUCT_FRACT(s32)
__STRUCT_FRACT(u32)
#undef __STRUCT_FRACT
-/*
- * Multiplies an integer by a fraction, while avoiding unnecessary
- * overflow or loss of precision.
- */
-#define mult_frac(x, numer, denom)( \
-{ \
- typeof(x) quot = (x) / (denom); \
- typeof(x) rem = (x) % (denom); \
- (quot * (numer)) + ((rem * (numer)) / (denom)); \
-} \
-)
+/* Calculate "x * n / d" without unnecessary overflow or loss of precision. */
+#define mult_frac(x, n, d) \
+({ \
+ typeof(x) x_ = (x); \
+ typeof(n) n_ = (n); \
+ typeof(d) d_ = (d); \
+ \
+ typeof(x_) q = x_ / d_; \
+ typeof(x_) r = x_ % d_; \
+ q * n_ + r * n_ / d_; \
+})
#define sector_div(a, b) do_div(a, b)