--- /Users/gwright/tmp/ghc-7-branch-Linker-patched/ghc/rts/ghc.mk	2010-12-19 13:32:23.000000000 -0500
+++ /Users/gwright/tmp/ghc-7-branch/ghc/rts/ghc.mk	2010-12-20 08:39:41.000000000 -0500
@@ -441,6 +441,11 @@
 rts_CC_OPTS		+= -DDTRACE
 rts_HC_OPTS		+= -DDTRACE
 
+# Apple's dtrace (the only one supported by ghc at the moment) uses
+# gcc as its preprocessor. If gcc isn't at /usr/bin/gcc, or we need
+# to force it to use a different gcc, we need to give the path in
+# the option cpppath.
+
 DTRACEPROBES_SRC = rts/RtsProbes.d
 $(DTRACEPROBES_H): $(DTRACEPROBES_SRC) includes/ghcplatform.h | $(dir $@)/.
 	"$(DTRACE)" $(filter -I%,$(rts_CC_OPTS)) -C -x cpppath=$(WhatGccIsCalled) -h -o $@ -s $<