* EXECUTABLE FILE STRUCTURE
***************************

OFFSET	SIZE	DESCRIPTION
------	----	-----------
$00	WORD	$601A - MAGIC WORD TO MAKE IT EXECUTABLE
$02	LONG	SIZE OF TEXT SEGMENT
$06	LONG	SIZE OF DATA SEGMENT
$0A	LONG	SIZE OF BSS  SEGMENT
$0E	LONG	SIZE OF SYMBOL TABLE
$12	LONG	RESERVED
$16	LONG	PRGFLAGS was reserved before GEMDOS 0.15 
$1A	WORD	ABSFLAG  was reserved before GEMDOS 0.15
$1C		TEXT SEGMENT
$1C+($02)		DATA SEGMENT
$1C+($02)+($06)		OPTIONAL SYMBOL TABLE
$1C+($02)+($06)+($0E)	FIXUP OFFSET
		OPTIONAL FIXUP RECORDS (FIXUP OFFSET >0)
		 FIXUP RECORDS ENDS WITH ZERO BYTE

	PRGFLAGS
	========
Bit 0	If set, Zero only the programs BSS
	If Clear, Zero all memory from end of program to stack start
Bit 1	If Set, Load into Alternate (Fast) RAM if possible
	If Clear, Load into normal RAM only.
Bit 2	If Set, Malloc will try to use Alternative (Fast) RAM
	If Clear, Malloc will only use normal RAM
	
DO NOT USE ALTERNATIVE RAM FOR ANYTHING THAT HAS SCREENS IN OR FOR ANYTHING
THAT USES DMA IN THAT MEMORY (e.g. STE Sound)

Bits 28-31	Used with Pexec() modes 0,3
	mode 7 has you passing PRGFLAGS to child as 2nd argument
	i.e. does not use its own PRGFLAGS
	see PEXEC.TXT
	
STANDARD SYMBOL TABLE consists of a number of records of the format:
---------------------
symbol_name	8 BYTES
symbol_type	WORD
symbol_value	LONG

SYMBOL TYPEs are defined as follows:
Defined		$8000
Equated		$4000
Global		$2000
Equated Register	$1000
External Reference	$800
Data Based Relocatable	$400
Text Based Relocatable	$200
BSS Based Relocatable	$100

NOTE:
    Symbol tables are free format and may differ from above.
    Alcyon use Alcyon Format symbols (as above)
    Mark Williams 2 use an empty segment and put symbols after the fixup info
    Mark Williams 3 put id header and debug info into symbol table as well

FIXUP OFFSET IS OFFSET OF FIRST LONGWORD THAT NEEDS ALTERING.
IF ABSFLAG>0 and/OR FIXUP OFFSET=0 THEN NO FIXUP TABLE
It is altered by adding the text segment start address to each longword.
OPTIONAL FIXUP RECORDS consist of bytes:
	    0 marks the end of the fixup information
	    1 add 254 to offset and get next offset byte
	2-254 add to offset and fix longword at that address
	NB:   odd bytes should not be used as all longwords
	      should start on even boundary.

HOW TO RELOCATE A FILE LOADED INTO MEMORY!
==========================================
* need to clear BSS segment and make enough room etc.
relocate	move.l	#file_addr,a2	;start of file to relocate
	cmp.w	#$601a,(a2)	;magic number - executable
	bne	rel_fail	;otherwise not
	lea	$1c(a2),a1	;start of text segment
	move.l	a1,d1
	move.l	a1,a0
	add.l	2(a2),a1	;add text size
	add.l	6(a2),a1	;add data size
	add.l	$a(a2),a1	;add symbol size
	clr.l	d0	;zero if o.k.
	tst.l	(a1)	;fixup offset null?
	beq	rel_end	;finished fixup!
	add.l	(a1)+,a0	;first fixup pointer
rel_add	add.l	d1,(a0)	;fixup long
rel_lp1	move.b	(a1)+,d0
	beq	rel_end	;zero marks finish
	cmp.b	#1,d0
	bne	add_ptr	
	add.w	#$00fe,a0	;add 254 to pointer if 1
	bra	rel_lp1
add_ptr	add.w	d0,a0	;add offset
	bra	rel_add
rel_fail	move.l	#-1,d0	;fail
rel_end	rts		;d0=already at zero if o.k.