svn commit: r228822 - head/sys/conf

[Alexander Best]

On Fri Dec 23 11, Dimitry Andric wrote:
> Author: dim
> Date: Fri Dec 23 00:23:37 2011
> New Revision: 228822
> URL: http://svn.freebsd.org/changeset/base/228822
> 
> Log:
>   When building the kernel with clang, it produces several warnings which
>   might be useful in some cases, but which are not severe enough to error
>   out the whole kernel build.  Display them anyway, so there is at least
>   some incentive to fix them eventually.
>   
>   Start with -Wtautological-compare warnings.  These usually occur when
>   people check if unsigned quantities are negative, or similar cases.  To
>   clean these up would be painful, and might give problems if the base
>   type which is compared against changes to signed later on.

... or is signed on one arch, but unsigned on another. ;)

any reason you add -Wno-error-tautological-compare to CWARNFLAGS seperately
and not in the upper CWARNFLAGS?= definition? the way you implemented it here
makes it impossible to specify custom CWARNFLAGS, where users might want to
keep -Wtautological-compare as an error and not turn it into a warning.

i already sent you the following patch, which takes a different approach
towards the issue you're trying to solve.

of course it's debatable, whether -Wno-error-tautological-compare should be
mandatory, or not. -fno-strict-aliasing e.g. is a flag which also gets appended
(only to COPTFLAGS) even when users set custom COPTFLAGS

cheers.
alex

>   
>   MFC after:	1 week
> 
> Modified:
>   head/sys/conf/kern.mk
> 
> Modified: head/sys/conf/kern.mk
> ==============================================================================
> --- head/sys/conf/kern.mk	Fri Dec 23 00:19:17 2011	(r228821)
> +++ head/sys/conf/kern.mk	Fri Dec 23 00:23:37 2011	(r228822)
> @@ -19,6 +19,10 @@ NO_WCONSTANT_CONVERSION=	-Wno-constant-c
>  NO_WARRAY_BOUNDS=		-Wno-array-bounds
>  NO_WSHIFT_COUNT_NEGATIVE=	-Wno-shift-count-negative
>  NO_WSHIFT_COUNT_OVERFLOW=	-Wno-shift-count-overflow
> +# Several other warnings which might be useful in some cases, but not severe
> +# enough to error out the whole kernel build.  Display them anyway, so there is
> +# some incentive to fix them eventually.
> +CWARNFLAGS+=	-Wno-error-tautological-compare
>  .endif
>  
>  #
-------------- next part --------------
Index: conf/kern.mk
===================================================================
--- conf/kern.mk	(revision 228556)
+++ conf/kern.mk	(working copy)
@@ -1,12 +1,24 @@
 # $FreeBSD$
 
 #
+# Clang implies -Wtautological-compare when -Wall was specified.  Since this
+# will produce errors for valid code, we need to disable -Wtautological-compare.
+# GCC doesn't recognize this warning, nor does it have a similar warning flag.
+# However specifying -Wextra implies -Wtautological-compare semantics.
+#
+.if ${CC:T:Mclang} == "clang"
+NO_TAUTCOMP=	-Wno-tautological-compare
+.else
+NO_TAUTCOMP=
+.endif
+
+#
 # Warning flags for compiling the kernel and components of the kernel:
 #
 CWARNFLAGS?=	-Wall -Wredundant-decls -Wnested-externs -Wstrict-prototypes \
 		-Wmissing-prototypes -Wpointer-arith -Winline -Wcast-qual \
 		-Wundef -Wno-pointer-sign -fformat-extensions \
-		-Wmissing-include-dirs -fdiagnostics-show-option
+		-Wmissing-include-dirs -fdiagnostics-show-option ${NO_TAUTCOMP}
 #
 # The following flags are next up for working on:
 #	-Wextra