Rather than require a makeoptions DEBUG to get debug correct,

add it in kern.mk, but only if we're using clang. While this
option is supported by both clang and gcc, in the future there
may be changes to clang which change the defaults that require
a tweak to build our kernel such that other tools in our tree
will work. Set a good example by forcing -gdwarf-2 only for
clang builds, and only if the user hasn't specified another
dwarf level already. Update UPDATING to reflect the changed
state of affairs. This also keeps us from having to update
all the ARM kernels to add this, and also keeps us from
in the future having to update all the MIPS kernels and is
one less place the user will have to know to do something
special for clang and one less thing developers will need
to do when moving an architecture to clang.

Reviewed by:	ian@
MFC after:	1 week

UPDATING

@@ -31,6 +31,13 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 11.x IS SLOW:
 	disable the most expensive debugging functionality run
 	"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20140325:
+	It is no longer necessary to include the dwarf version in your DEBUG
+	options in your kernel config file. The bug that required it to be
+	placed in the config file has bene fixed. DEBUG should now just
+	contain -g. The build system will automatically update things
+	to do the right thing. Ignore the entry from 20140216.
+
 20140306:
 	Support for libwrap (TCP wrappers) in rpcbind was disabled by default
 	to improve performance.  To re-enable it, if needed, run rpcbind
@@ -44,16 +51,18 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 11.x IS SLOW:
 	to do so. Set WITHOUT_GPL_DTC if you require the BSDL compiler.
 
 20140216:
-	Clang and llvm have been upgraded to 3.4 release.  Please note that
-	clang 3.4 now defaults to DWARF4 debug information format when you
-	specify -g.  Since kgdb(1) only supports DWARF2, you should update any
-	customized kernel configurations which include debug information to
-	explicitly use -gdwarf-2, e.g:
+	Clang and llvm have been upgraded to 3.4 release.
+
+	Please note that clang 3.4 now defaults to DWARF4 debug information
+	format when you specify -g.  Since kgdb(1) only supports DWARF2, you
+	should update any customized kernel configurations which include debug
+	information to explicitly use -gdwarf-2, e.g:
 
 	  makeoptions	DEBUG=-gdwarf-2
 
 	This has already been applied to the appropriate GENERIC configuration
 	files, so if you inherit from those, no changes are required.
+	Please note: this bug has been fixed, please see 20140325.
 
 20140216:
 	The nve(4) driver has been removed.  Please use the nfe(4) driver

sys/amd64/conf/GENERIC

@@ -21,7 +21,7 @@
 cpu		HAMMER
 ident		GENERIC
 
-makeoptions	DEBUG=-gdwarf-2		# Build kernel with gdb(1) debug symbols
+makeoptions	DEBUG=-g
 makeoptions	WITH_CTF=1		# Run ctfconvert(1) for DTrace support
 
 options 	SCHED_ULE		# ULE scheduler

sys/conf/kern.mk

@@ -162,3 +162,10 @@ CFLAGS+=	-ffreestanding
     ${MACHINE_CPUARCH} != "arm" && ${MACHINE_CPUARCH} != "mips"
 CFLAGS+=	-fstack-protector
 .endif
+
+#
+# Add -gdwarf-2 when compiling -g
+#
+.if ${COMPILER_TYPE} == "clang" && ${CFLAGS:M-g} != "" && ${CFLAGS:M-gdwarf} == ""
+CFLAGS+=	-gdwarf-2
+.endif

sys/i386/conf/GENERIC

@@ -23,7 +23,7 @@ cpu		I586_CPU
 cpu		I686_CPU
 ident		GENERIC
 
-makeoptions	DEBUG=-gdwarf-2		# Build kernel with gdb(1) debug symbols
+makeoptions	DEBUG=-g
 makeoptions	WITH_CTF=1		# Run ctfconvert(1) for DTrace support
 
 options 	SCHED_ULE		# ULE scheduler

sys/i386/conf/XEN

@@ -6,7 +6,7 @@
 cpu		I686_CPU
 ident		XEN
 
-makeoptions	DEBUG=-gdwarf-2		# Build kernel with gdb(1) debug symbols
+makeoptions	DEBUG=-g
 makeoptions	WITHOUT_MODULES="aha ahb amd ctl cxgb dpt drm drm2 hptnr hptmv ida malo mps mwl rdma sound sym trm xfs"
 
 options 	SCHED_ULE		# ULE scheduler

sys/sparc64/conf/GENERIC

@@ -21,7 +21,7 @@
 cpu		SUN4U
 ident		GENERIC
 
-makeoptions	DEBUG=-gdwarf-2		# Build kernel with gdb(1) debug symbols
+makeoptions	DEBUG=-g
 
 # Platforms supported
 #	At this time all platforms are supported, as-is.