* doc/internals.texi (Relaxing with a table) <after relaxation>:

Point out caveats with generating fixups for the opcode in a frag.

gas/ChangeLog

@@ -1,3 +1,8 @@
+2000-12-31  Hans-Peter Nilsson  <hp@bitrange.com>
+
+	* doc/internals.texi (Relaxing with a table) <after relaxation>:
+	Point out caveats with generating fixups for the opcode in a frag.
+
 Sat Dec 30 19:02:48 MET 2000  Jan Hubicka  <jh@suse.cz>
 
 	* configure.in: Add support for x86_64 and x86_64-*-linux-gnu*

gas/doc/internals.texi

@@ -1601,6 +1601,16 @@ called to convert the frag to an @code{rs_fill} frag with no variant part.
 Sometimes changing addressing modes may also require rewriting the instruction.
 It can be accessed via @code{fr_opcode} or @code{fr_fix}.
 
+If you generate frags separately for the basic insn opcode and any relaxable
+operands, do not call @code{fix_new} thinking you can emit fixups for the
+opcode field from the relaxable frag.  It is not garanteed to be the same frag.
+If you need to emit fixups for the opcode field from inspection of the
+relaxable frag, then you need to generate a common frag for both the basic
+opcode and relaxable fields, or you need to provide the frag for the opcode to
+pass to @code{fix_new}.  The latter can be done for example by defining
+@code{TC_FRAG_TYPE} to include a pointer to it and defining @code{TC_FRAG_INIT}
+to set the pointer.
+
 Sometimes @code{fr_var} is increased instead, and @code{frag_wane} is not
 called.  I'm not sure, but I think this is to keep @code{fr_fix} referring to
 an earlier byte, and @code{fr_subtype} set to @code{rs_machine_dependent} so