===================================================================
@@ -59,6 +59,14 @@ these include the autoconfigured headers
machine.
@item
@file{tm_p.h}, which includes the header @file{@var{machine}-protos.h}
-that contains prototypes for functions in the target @file{.c} file.
-FIXME: why is such a separate header necessary?
+that contains prototypes for functions in the target
+@file{@var{machine}.c} file. The header @file{@var{machine}-protos.h}
+can include prototypes of functions that use rtl and tree data
+structures inside appropriate @code{#ifdef RTX_CODE} and @code{#ifdef
+TREE_CODE} conditional code segements. The
+@file{@var{machine}-protos.h} is included after the @file{rtl.h}
+and/or @file{tree.h} would have been included. The @file{tm_p.h} also
+includes the header @file{tm-preds.h} which is generated by
+@file{genpreds} program during the build to define the declarations
+and inline functions for the predicate functions.
@end itemize