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SubjectRe: [IDEA+RFC] Possible solution for min()/max() war
Hi,

On Fri, 31 Aug 2001, Peter T. Breuer wrote:

> > What bug are you trying to fix here?
>
> Wake up!

I'm trying.

> Try reading the last 10 days kernel messages. The last 48 hours are
> particularly rewarding.

I have, but I only get the feeling, we're hunting here for imaginary bugs.
Real bugs could be found with -Wsign-compare, but nobody wants to use it
because our master doesn't want it...
Please define the bugs first, you're trying to fix! If you don't like
-Wsign-compare, consider defining rules for the Stanford checker. This way
you can check all compares and not just the few uses of min.

> C silently transforms signed int to unsigned int in cross-signed
> comparisons. This results in 1U < -2, and gives rise to all kinds
> of error paths from min/max codes (in particular, but they're not
> all) of the form

Care to give an example? For the cases I tried gcc gave a warning.

> Linus wants possible mistakes flagged. He specifically does not want
> -Wsign-compare because it apparently gives false positives.

diff -u -r1.1.1.23 Makefile
--- Makefile 16 Aug 2001 20:50:22 -0000 1.1.1.23
+++ Makefile 31 Aug 2001 11:15:21 -0000
@@ -87,7 +87,11 @@

CPPFLAGS := -D__KERNEL__ -I$(HPATH)

-CFLAGS := $(CPPFLAGS) -Wall -Wstrict-prototypes -Wno-trigraphs -O2 \
+WFLAGS := -Wall -Wstrict-prototypes -Wno-trigraphs
+ifdef CONFIG_EXTRA_WARNINGS
+WFLAGS := $(WFLAGS) -Wsign-compare
+endif
+CFLAGS := $(CPPFLAGS) $(WFLAGS) -O2 \
-fomit-frame-pointer -fno-strict-aliasing -fno-common
AFLAGS := -D__ASSEMBLY__ $(CPPFLAGS)

diff -u -r1.1.1.15 config.in
--- arch/i386/config.in 21 Jul 2001 12:48:20 -0000 1.1.1.15
+++ arch/i386/config.in 31 Aug 2001 11:12:56 -0000
@@ -390,4 +390,5 @@

#bool 'Debug kmalloc/kfree' CONFIG_DEBUG_MALLOC
bool 'Magic SysRq key' CONFIG_MAGIC_SYSRQ
+bool 'Extra compile warnings' CONFIG_EXTRA_WARNINGS
endmenu
diff -u -r1.1.1.23 Configure.help
--- Documentation/Configure.help 16 Aug 2001 20:55:53 -0000 1.1.1.23
+++ Documentation/Configure.help 31 Aug 2001 11:21:10 -0000
@@ -15766,6 +15766,15 @@
keys are documented in Documentation/sysrq.txt. Don't say Y unless
you really know what this hack does.

+Extra compile warnings
+CONFIG_EXTRA_WARNINGS
+ If you say Y here, the compilation will generate lots of extra
+ warnings. Some of them warn about constructions that users generally
+ do not consider questionable, but which occasionally you might wish
+ to check for; others warn about constructions that are necessary or
+ hard to avoid in some cases, and there is no simple way to modify the
+ code to suppress the warning. Unless you look for bugs, say N.
+
ISDN subsystem
CONFIG_ISDN
ISDN ("Integrated Services Digital Networks", called RNIS in France)
bye, Roman




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