* [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
@ 2012-08-31 15:02 Guenter Roeck
2012-08-31 19:38 ` Andrew Morton
2012-09-09 14:57 ` Geert Uytterhoeven
0 siblings, 2 replies; 9+ messages in thread
From: Guenter Roeck @ 2012-08-31 15:02 UTC (permalink / raw)
To: linux-kernel
Cc: Andrew Morton, Pekka Enberg, Ingo Molnar, H. Peter Anvin,
Jean Delvare, lm-sensors, Guenter Roeck
DIV_ROUND_CLOSEST returns a bad result for negative dividends:
DIV_ROUND_CLOSEST(-2, 2) = 0
Most of the time this does not matter. However, in the hardware monitoring
subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
negative (such as temperatures).
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
---
v4: Don't address negative divisors to improve chances for compile-time
optimization. Document DIV_ROUND_CLOSEST macro.
v3: Instead of adding a new macro, fix DIV_ROUND_CLOSEST.
This version works for negative dividend and divisor.
v2: v1 did not work if typeof(divisor) was an unsigned variable type
(which can obviously not be negative).
Rework to revert to DIV_ROUND_CLOSEST if the dividend is unsigned,
or if it is signed but non-negative.
include/linux/kernel.h | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 6043821..594b419 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -82,10 +82,18 @@
__x - (__x % (y)); \
} \
)
+
+/*
+ * Divide positive or negative dividend by positive divisor and round
+ * to closest integer. Result is undefined for negative divisors.
+ */
#define DIV_ROUND_CLOSEST(x, divisor)( \
{ \
- typeof(divisor) __divisor = divisor; \
- (((x) + ((__divisor) / 2)) / (__divisor)); \
+ typeof(x) __x = x; \
+ typeof(divisor) __d = divisor; \
+ (((typeof(x))-1) >= 0 || (__x) >= 0) ? \
+ (((__x) + ((__d) / 2)) / (__d)) : \
+ (((__x) - ((__d) / 2)) / (__d)); \
} \
)
--
1.7.9.7
^ permalink raw reply related [flat|nested] 9+ messages in thread
* Re: [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
2012-08-31 15:02 [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends Guenter Roeck
@ 2012-08-31 19:38 ` Andrew Morton
2012-08-31 21:05 ` Guenter Roeck
2012-09-01 17:02 ` Jean Delvare
2012-09-09 14:57 ` Geert Uytterhoeven
1 sibling, 2 replies; 9+ messages in thread
From: Andrew Morton @ 2012-08-31 19:38 UTC (permalink / raw)
To: Guenter Roeck
Cc: linux-kernel, Pekka Enberg, Ingo Molnar, H. Peter Anvin,
Jean Delvare, lm-sensors
On Fri, 31 Aug 2012 08:02:19 -0700
Guenter Roeck <linux@roeck-us.net> wrote:
> DIV_ROUND_CLOSEST returns a bad result for negative dividends:
> DIV_ROUND_CLOSEST(-2, 2) = 0
>
> Most of the time this does not matter. However, in the hardware monitoring
> subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
> negative (such as temperatures).
>
> ...
>
> +
> +/*
> + * Divide positive or negative dividend by positive divisor and round
> + * to closest integer. Result is undefined for negative divisors.
> + */
> #define DIV_ROUND_CLOSEST(x, divisor)( \
> { \
> - typeof(divisor) __divisor = divisor; \
> - (((x) + ((__divisor) / 2)) / (__divisor)); \
> + typeof(x) __x = x; \
> + typeof(divisor) __d = divisor; \
> + (((typeof(x))-1) >= 0 || (__x) >= 0) ? \
> + (((__x) + ((__d) / 2)) / (__d)) : \
> + (((__x) - ((__d) / 2)) / (__d)); \
> } \
Looks good to me. The patch causes no change in text size for
kernel/sched/fair.o and drivers/cpuidle/governors/menu.o, so it seems
that the cc trickery is working.
I'll add it to my tree for testing - please merge this via your tree.
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
2012-08-31 19:38 ` Andrew Morton
@ 2012-08-31 21:05 ` Guenter Roeck
2012-09-01 17:02 ` Jean Delvare
1 sibling, 0 replies; 9+ messages in thread
From: Guenter Roeck @ 2012-08-31 21:05 UTC (permalink / raw)
To: Andrew Morton
Cc: linux-kernel, Pekka Enberg, Ingo Molnar, H. Peter Anvin,
Jean Delvare, lm-sensors
On Fri, Aug 31, 2012 at 12:38:12PM -0700, Andrew Morton wrote:
> On Fri, 31 Aug 2012 08:02:19 -0700
> Guenter Roeck <linux@roeck-us.net> wrote:
>
> > DIV_ROUND_CLOSEST returns a bad result for negative dividends:
> > DIV_ROUND_CLOSEST(-2, 2) = 0
> >
> > Most of the time this does not matter. However, in the hardware monitoring
> > subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
> > negative (such as temperatures).
> >
> > ...
> >
> > +
> > +/*
> > + * Divide positive or negative dividend by positive divisor and round
> > + * to closest integer. Result is undefined for negative divisors.
> > + */
> > #define DIV_ROUND_CLOSEST(x, divisor)( \
> > { \
> > - typeof(divisor) __divisor = divisor; \
> > - (((x) + ((__divisor) / 2)) / (__divisor)); \
> > + typeof(x) __x = x; \
> > + typeof(divisor) __d = divisor; \
> > + (((typeof(x))-1) >= 0 || (__x) >= 0) ? \
> > + (((__x) + ((__d) / 2)) / (__d)) : \
> > + (((__x) - ((__d) / 2)) / (__d)); \
> > } \
>
> Looks good to me. The patch causes no change in text size for
> kernel/sched/fair.o and drivers/cpuidle/governors/menu.o, so it seems
> that the cc trickery is working.
>
> I'll add it to my tree for testing - please merge this via your tree.
>
Will do.
Thanks,
Guenter
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
2012-08-31 19:38 ` Andrew Morton
2012-08-31 21:05 ` Guenter Roeck
@ 2012-09-01 17:02 ` Jean Delvare
2012-09-02 2:14 ` Guenter Roeck
1 sibling, 1 reply; 9+ messages in thread
From: Jean Delvare @ 2012-09-01 17:02 UTC (permalink / raw)
To: Andrew Morton
Cc: Guenter Roeck, linux-kernel, Pekka Enberg, Ingo Molnar,
H. Peter Anvin, lm-sensors
Hi Andrew, Guenter,
On Fri, 31 Aug 2012 12:38:12 -0700, Andrew Morton wrote:
> On Fri, 31 Aug 2012 08:02:19 -0700
> Guenter Roeck <linux@roeck-us.net> wrote:
>
> > DIV_ROUND_CLOSEST returns a bad result for negative dividends:
> > DIV_ROUND_CLOSEST(-2, 2) = 0
> >
> > Most of the time this does not matter. However, in the hardware monitoring
> > subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
> > negative (such as temperatures).
> >
> > ...
> >
> > +
> > +/*
> > + * Divide positive or negative dividend by positive divisor and round
> > + * to closest integer. Result is undefined for negative divisors.
> > + */
> > #define DIV_ROUND_CLOSEST(x, divisor)( \
> > { \
> > - typeof(divisor) __divisor = divisor; \
> > - (((x) + ((__divisor) / 2)) / (__divisor)); \
> > + typeof(x) __x = x; \
> > + typeof(divisor) __d = divisor; \
> > + (((typeof(x))-1) >= 0 || (__x) >= 0) ? \
> > + (((__x) + ((__d) / 2)) / (__d)) : \
> > + (((__x) - ((__d) / 2)) / (__d)); \
> > } \
>
> Looks good to me.
My testing looks good too.
Acked-by: Jean Delvare <khali@linux-fr.org>
> The patch causes no change in text size for
> kernel/sched/fair.o and drivers/cpuidle/governors/menu.o, so it seems
> that the cc trickery is working.
Indeed. I looked for test size increase, and for my config, besides
hwmon, I only spotted the following ones:
drivers/media/rc/mceusb.o
drivers/gpu/drm/i915/intel_pm.o
drivers/tty/serial/pch_uart.o
These don't look like hot paths, so I'd say we don't care. Plus the
intel_pm one can probably be solved by using an unsigned int, I don't
see why/how ia_freq could be negative (negative frequency anyone?) And
for mceusb it can be solved easily by changing "1" to "1U".
For hwmon drivers, we typically only use DIV_ROUND_CLOSEST when the
user changes a setting, this isn't a frequent event. Plus, this is
exactly the case we are fixing here, as temperature limits, and to a
lesser extent voltage limits, can be negative.
> I'll add it to my tree for testing - please merge this via your tree.
--
Jean Delvare
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
2012-09-01 17:02 ` Jean Delvare
@ 2012-09-02 2:14 ` Guenter Roeck
0 siblings, 0 replies; 9+ messages in thread
From: Guenter Roeck @ 2012-09-02 2:14 UTC (permalink / raw)
To: Jean Delvare
Cc: Andrew Morton, linux-kernel, Pekka Enberg, Ingo Molnar,
H. Peter Anvin, lm-sensors
On Sat, Sep 01, 2012 at 07:02:54PM +0200, Jean Delvare wrote:
> Hi Andrew, Guenter,
>
> On Fri, 31 Aug 2012 12:38:12 -0700, Andrew Morton wrote:
> > On Fri, 31 Aug 2012 08:02:19 -0700
> > Guenter Roeck <linux@roeck-us.net> wrote:
> >
> > > DIV_ROUND_CLOSEST returns a bad result for negative dividends:
> > > DIV_ROUND_CLOSEST(-2, 2) = 0
> > >
> > > Most of the time this does not matter. However, in the hardware monitoring
> > > subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
> > > negative (such as temperatures).
> > >
> > > ...
> > >
> > > +
> > > +/*
> > > + * Divide positive or negative dividend by positive divisor and round
> > > + * to closest integer. Result is undefined for negative divisors.
> > > + */
> > > #define DIV_ROUND_CLOSEST(x, divisor)( \
> > > { \
> > > - typeof(divisor) __divisor = divisor; \
> > > - (((x) + ((__divisor) / 2)) / (__divisor)); \
> > > + typeof(x) __x = x; \
> > > + typeof(divisor) __d = divisor; \
> > > + (((typeof(x))-1) >= 0 || (__x) >= 0) ? \
> > > + (((__x) + ((__d) / 2)) / (__d)) : \
> > > + (((__x) - ((__d) / 2)) / (__d)); \
> > > } \
> >
> > Looks good to me.
>
> My testing looks good too.
>
> Acked-by: Jean Delvare <khali@linux-fr.org>
>
Thanks a lot!
> > The patch causes no change in text size for
> > kernel/sched/fair.o and drivers/cpuidle/governors/menu.o, so it seems
> > that the cc trickery is working.
>
> Indeed. I looked for test size increase, and for my config, besides
> hwmon, I only spotted the following ones:
>
> drivers/media/rc/mceusb.o
> drivers/gpu/drm/i915/intel_pm.o
> drivers/tty/serial/pch_uart.o
>
> These don't look like hot paths, so I'd say we don't care. Plus the
> intel_pm one can probably be solved by using an unsigned int, I don't
> see why/how ia_freq could be negative (negative frequency anyone?) And
> for mceusb it can be solved easily by changing "1" to "1U".
>
Yes, it helps a lot that the C trickery optimizes the changes away most of the time.
I'll let the patch rest in -next for a few more days before I send it to Linus.
Guenter
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
2012-08-31 15:02 [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends Guenter Roeck
2012-08-31 19:38 ` Andrew Morton
@ 2012-09-09 14:57 ` Geert Uytterhoeven
2012-09-09 16:17 ` Guenter Roeck
1 sibling, 1 reply; 9+ messages in thread
From: Geert Uytterhoeven @ 2012-09-09 14:57 UTC (permalink / raw)
To: Guenter Roeck
Cc: linux-kernel, Andrew Morton, Pekka Enberg, Ingo Molnar,
H. Peter Anvin, Jean Delvare, lm-sensors
On Fri, Aug 31, 2012 at 5:02 PM, Guenter Roeck <linux@roeck-us.net> wrote:
> DIV_ROUND_CLOSEST returns a bad result for negative dividends:
> DIV_ROUND_CLOSEST(-2, 2) = 0
>
> Most of the time this does not matter. However, in the hardware monitoring
> subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
> negative (such as temperatures).
This seems to cause 3 new warnings in my m68k builds of v3.6-rc5:
drivers/hwmon/mcp3021.c:76: warning: comparison is always true due to
limited range of data type
drivers/ide/ide-cd.c:1158: warning: comparison is always true due to
limited range of data type
drivers/ide/ide-cd.c:1159: warning: comparison is always true due to
limited range of data type
$ m68k-linux-gnu-gcc -v
Using built-in specs.
Target: m68k-linux-gnu
Configured with: ../src/configure -v --enable-languages=c,c++
--prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib
--without-included-gettext --enable-threads=posix --enable-nls
--with-gxx-include-dir=/usr/m68k-linux-gnu/include/c++/4.1.2
--program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
--enable-libstdcxx-debug --disable-libssp --disable-werror
--enable-checking=release --program-prefix=m68k-linux-gnu-
--includedir=/usr/m68k-linux-gnu/include --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=m68k-linux-gnu
Thread model: posix
gcc version 4.1.2 20061115 (prerelease) (Ubuntu 4.1.1-21)
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
2012-09-09 14:57 ` Geert Uytterhoeven
@ 2012-09-09 16:17 ` Guenter Roeck
2012-09-09 20:38 ` Geert Uytterhoeven
0 siblings, 1 reply; 9+ messages in thread
From: Guenter Roeck @ 2012-09-09 16:17 UTC (permalink / raw)
To: Geert Uytterhoeven
Cc: linux-kernel, Andrew Morton, Pekka Enberg, Ingo Molnar,
H. Peter Anvin, Jean Delvare, lm-sensors
On Sun, Sep 09, 2012 at 04:57:34PM +0200, Geert Uytterhoeven wrote:
> On Fri, Aug 31, 2012 at 5:02 PM, Guenter Roeck <linux@roeck-us.net> wrote:
> > DIV_ROUND_CLOSEST returns a bad result for negative dividends:
> > DIV_ROUND_CLOSEST(-2, 2) = 0
> >
> > Most of the time this does not matter. However, in the hardware monitoring
> > subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
> > negative (such as temperatures).
>
> This seems to cause 3 new warnings in my m68k builds of v3.6-rc5:
>
> drivers/hwmon/mcp3021.c:76: warning: comparison is always true due to
> limited range of data type
> drivers/ide/ide-cd.c:1158: warning: comparison is always true due to
> limited range of data type
> drivers/ide/ide-cd.c:1159: warning: comparison is always true due to
> limited range of data type
>
> $ m68k-linux-gnu-gcc -v
> Using built-in specs.
> Target: m68k-linux-gnu
> Configured with: ../src/configure -v --enable-languages=c,c++
> --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib
> --without-included-gettext --enable-threads=posix --enable-nls
> --with-gxx-include-dir=/usr/m68k-linux-gnu/include/c++/4.1.2
> --program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
> --enable-libstdcxx-debug --disable-libssp --disable-werror
> --enable-checking=release --program-prefix=m68k-linux-gnu-
> --includedir=/usr/m68k-linux-gnu/include --build=x86_64-linux-gnu
> --host=x86_64-linux-gnu --target=m68k-linux-gnu
> Thread model: posix
> gcc version 4.1.2 20061115 (prerelease) (Ubuntu 4.1.1-21)
>
Hi Gert,
The "always true" condition is on purpose to cause the compiler to optimize the
expression away. I don't see the warnings myself, on none of the targets I am
building (x86, ppc, arm, mips), but then I am using much more recent compiler
versions. Odd is that you only see the warnings on "u16" and not elsewhere.
I don't immediately see the warnings with a more recent m68k compiler (4.6.3),
nor with any other target (x86, ppc, arm, mips) in my nightly builds.
Can you send me your configuration ?
Also, do you know where I can find the Ubuntu/Debian package for your compiler
version, by any chance ?
Thanks,
Guenter
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
2012-09-09 16:17 ` Guenter Roeck
@ 2012-09-09 20:38 ` Geert Uytterhoeven
2012-09-09 21:30 ` Guenter Roeck
0 siblings, 1 reply; 9+ messages in thread
From: Geert Uytterhoeven @ 2012-09-09 20:38 UTC (permalink / raw)
To: Guenter Roeck
Cc: linux-kernel, Andrew Morton, Pekka Enberg, Ingo Molnar,
H. Peter Anvin, Jean Delvare, lm-sensors
Hi Günter,
On Sun, Sep 9, 2012 at 6:17 PM, Guenter Roeck <linux@roeck-us.net> wrote:
> On Sun, Sep 09, 2012 at 04:57:34PM +0200, Geert Uytterhoeven wrote:
>> On Fri, Aug 31, 2012 at 5:02 PM, Guenter Roeck <linux@roeck-us.net> wrote:
>> > DIV_ROUND_CLOSEST returns a bad result for negative dividends:
>> > DIV_ROUND_CLOSEST(-2, 2) = 0
>> >
>> > Most of the time this does not matter. However, in the hardware monitoring
>> > subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
>> > negative (such as temperatures).
>>
>> This seems to cause 3 new warnings in my m68k builds of v3.6-rc5:
>>
>> drivers/hwmon/mcp3021.c:76: warning: comparison is always true due to
>> limited range of data type
>> drivers/ide/ide-cd.c:1158: warning: comparison is always true due to
>> limited range of data type
>> drivers/ide/ide-cd.c:1159: warning: comparison is always true due to
>> limited range of data type
>>
>> $ m68k-linux-gnu-gcc -v
>> Using built-in specs.
>> Target: m68k-linux-gnu
>> Configured with: ../src/configure -v --enable-languages=c,c++
>> --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib
>> --without-included-gettext --enable-threads=posix --enable-nls
>> --with-gxx-include-dir=/usr/m68k-linux-gnu/include/c++/4.1.2
>> --program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
>> --enable-libstdcxx-debug --disable-libssp --disable-werror
>> --enable-checking=release --program-prefix=m68k-linux-gnu-
>> --includedir=/usr/m68k-linux-gnu/include --build=x86_64-linux-gnu
>> --host=x86_64-linux-gnu --target=m68k-linux-gnu
>> Thread model: posix
>> gcc version 4.1.2 20061115 (prerelease) (Ubuntu 4.1.1-21)
>>
> The "always true" condition is on purpose to cause the compiler to optimize the
> expression away. I don't see the warnings myself, on none of the targets I am
> building (x86, ppc, arm, mips), but then I am using much more recent compiler
> versions. Odd is that you only see the warnings on "u16" and not elsewhere.
>
> I don't immediately see the warnings with a more recent m68k compiler (4.6.3),
> nor with any other target (x86, ppc, arm, mips) in my nightly builds.
I also don't see it in any of the linux-next builds of v3.6-rc5. So
probably it's just
a gcc 4.1.2 issue...
> Can you send me your configuration ?
The ide-cd one shows up in any config that enables ide-cd, incl. defconfig and
allmodconfig.
The mcp3021 one I only see in allmodconfig.
> Also, do you know where I can find the Ubuntu/Debian package for your compiler
> version, by any chance ?
It's not from an official binary package. I built the cross-compiler
from the then
current gcc 4.1.1-21 sources in Ubuntu.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends
2012-09-09 20:38 ` Geert Uytterhoeven
@ 2012-09-09 21:30 ` Guenter Roeck
0 siblings, 0 replies; 9+ messages in thread
From: Guenter Roeck @ 2012-09-09 21:30 UTC (permalink / raw)
To: Geert Uytterhoeven
Cc: linux-kernel, Andrew Morton, Pekka Enberg, Ingo Molnar,
H. Peter Anvin, Jean Delvare, lm-sensors
On Sun, Sep 09, 2012 at 10:38:41PM +0200, Geert Uytterhoeven wrote:
> Hi Günter,
>
> On Sun, Sep 9, 2012 at 6:17 PM, Guenter Roeck <linux@roeck-us.net> wrote:
> > On Sun, Sep 09, 2012 at 04:57:34PM +0200, Geert Uytterhoeven wrote:
> >> On Fri, Aug 31, 2012 at 5:02 PM, Guenter Roeck <linux@roeck-us.net> wrote:
> >> > DIV_ROUND_CLOSEST returns a bad result for negative dividends:
> >> > DIV_ROUND_CLOSEST(-2, 2) = 0
> >> >
> >> > Most of the time this does not matter. However, in the hardware monitoring
> >> > subsystem, DIV_ROUND_CLOSEST is sometimes used on integers which can be
> >> > negative (such as temperatures).
> >>
> >> This seems to cause 3 new warnings in my m68k builds of v3.6-rc5:
> >>
> >> drivers/hwmon/mcp3021.c:76: warning: comparison is always true due to
> >> limited range of data type
> >> drivers/ide/ide-cd.c:1158: warning: comparison is always true due to
> >> limited range of data type
> >> drivers/ide/ide-cd.c:1159: warning: comparison is always true due to
> >> limited range of data type
> >>
> >> $ m68k-linux-gnu-gcc -v
> >> Using built-in specs.
> >> Target: m68k-linux-gnu
> >> Configured with: ../src/configure -v --enable-languages=c,c++
> >> --prefix=/usr --enable-shared --with-system-zlib --libexecdir=/usr/lib
> >> --without-included-gettext --enable-threads=posix --enable-nls
> >> --with-gxx-include-dir=/usr/m68k-linux-gnu/include/c++/4.1.2
> >> --program-suffix=-4.1 --enable-__cxa_atexit --enable-clocale=gnu
> >> --enable-libstdcxx-debug --disable-libssp --disable-werror
> >> --enable-checking=release --program-prefix=m68k-linux-gnu-
> >> --includedir=/usr/m68k-linux-gnu/include --build=x86_64-linux-gnu
> >> --host=x86_64-linux-gnu --target=m68k-linux-gnu
> >> Thread model: posix
> >> gcc version 4.1.2 20061115 (prerelease) (Ubuntu 4.1.1-21)
> >>
> > The "always true" condition is on purpose to cause the compiler to optimize the
> > expression away. I don't see the warnings myself, on none of the targets I am
> > building (x86, ppc, arm, mips), but then I am using much more recent compiler
> > versions. Odd is that you only see the warnings on "u16" and not elsewhere.
> >
> > I don't immediately see the warnings with a more recent m68k compiler (4.6.3),
> > nor with any other target (x86, ppc, arm, mips) in my nightly builds.
>
> I also don't see it in any of the linux-next builds of v3.6-rc5. So
> probably it's just
> a gcc 4.1.2 issue...
>
> > Can you send me your configuration ?
>
> The ide-cd one shows up in any config that enables ide-cd, incl. defconfig and
> allmodconfig.
> The mcp3021 one I only see in allmodconfig.
>
I tried both and did not see the problem. I agree, it does look like a compiler
version problem.
> > Also, do you know where I can find the Ubuntu/Debian package for your compiler
> > version, by any chance ?
>
> It's not from an official binary package. I built the cross-compiler
> from the then
> current gcc 4.1.1-21 sources in Ubuntu.
>
Ok.
Just in case you are interested, I installed the m68k cross-compiler from
deb http://www.freewrt.org/~tg/debs68k/ cross main
For my other targets, I use Yocto builds.
I think I'll let this go as false positive for now, unless there are problems
with more recent compilers.
Thanks,
Guenter
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2012-09-09 21:30 UTC | newest]
Thread overview: 9+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2012-08-31 15:02 [PATCH v4] linux/kernel.h: Fix DIV_ROUND_CLOSEST to support negative dividends Guenter Roeck
2012-08-31 19:38 ` Andrew Morton
2012-08-31 21:05 ` Guenter Roeck
2012-09-01 17:02 ` Jean Delvare
2012-09-02 2:14 ` Guenter Roeck
2012-09-09 14:57 ` Geert Uytterhoeven
2012-09-09 16:17 ` Guenter Roeck
2012-09-09 20:38 ` Geert Uytterhoeven
2012-09-09 21:30 ` Guenter Roeck
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