4.4BSD/usr/src/contrib/gas-1.38/subsegs.h

/* subsegs.h -> subsegs.c
   Copyright (C) 1987 Free Software Foundation, Inc.

This file is part of GAS, the GNU Assembler.

GAS is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 1, or (at your option)
any later version.

GAS is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GAS; see the file COPYING.  If not, write to
the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.  */

/*
 * For every sub-segment the user mentions in the ASsembler program,
 * we make one struct frchain. Each sub-segment has exactly one struct frchain
 * and vice versa.
 *
 * Struct frchain's are forward chained (in ascending order of sub-segment
 * code number). The chain runs through frch_next of each subsegment.
 * This makes it hard to find a subsegment's frags
 * if programmer uses a lot of them. Most programs only use text0 and
 * data0, so they don't suffer. At least this way:
 * (1)	There are no "arbitrary" restrictions on how many subsegments
 *	can be programmed;
 * (2)	Subsegments' frchain-s are (later) chained together in the order in
 *	which they are emitted for object file viz text then data.
 *
 * From each struct frchain dangles a chain of struct frags. The frags
 * represent code fragments, for that sub-segment, forward chained.
 */

struct frchain			/* control building of a frag chain */
{				/* FRCH = FRagment CHain control */
  struct frag *	frch_root;	/* 1st struct frag in chain, or NULL */
  struct frag *	frch_last;	/* last struct frag in chain, or NULL */
  struct frchain * frch_next;	/* next in chain of struct frchain-s */
  segT		frch_seg;	/* SEG_TEXT or SEG_DATA. */
  subsegT	frch_subseg;	/* subsegment number of this chain */
};

typedef struct frchain frchainS;

extern frchainS * frchain_root;	/* NULL means no frchains yet. */
				/* all subsegments' chains hang off here */

extern frchainS * frchain_now;
				/* Frchain we are assembling into now */
				/* That is, the current segment's frag */
				/* chain, even if it contains no (complete) */
				/* frags. */

extern frchainS * data0_frchainP;
				/* Sentinel for frchain crawling. */
				/* Points to the 1st data-segment frchain. */
				/* (Which is pointed to by the last text- */
				/* segment frchain.) */

/* end: subsegs.h */