README.binfmt

8bit/some 16bit platforms

	magic XX YY		; magic is the CPU specific magic
				; XX and YY are any value
				; used to form a jump around the header
	FZX1			; format magic (general)
	loadpage.b		; 0 means 'relocatable'
	chmem.w			; chmem value (0 all, will change to stack)
	code.w			; size of code segment
	data.w			; size of data segment
	bss.w			; size of the BSS
	0.w			; reserved

Header is intentionally part of the code so that we load aligned blocks into
memory fast. The binary ends with the last block of data (and if need be
some zeros of the BSS but see below)

Address of code is deliberately passed into the crt0.S from kernel for
relocators to be possible

Proposed changes:
	One new magic for split I/D on relevant platforms
	chmem size will become stack size (only breaks stuff with it set)
	0 base will mean 'has relocations'
	BSS will start with relocation data

	0.w will become
		cpufeature.b
		cpuspecific.b

	6502/68HC11 will use cpuspecific.b for ZP space needed

	The CPUfeature bit is bits for features not CPU subtypes as
	o65 does it so

	6502 bits
	0:	NMOS illegals		6502 only
	1:	65C02			65C02 and friends
	2:	65C02 bitops		Rockwell and later WDC C02
	3:	65CE02	(Z)		65CE02
	4:	BCD			All but 2A03
	5:	65C802/816
	6-7 spare for 740 family etc
	[don't need to cover kernel only bits]

	This way means we can just do an and and a compare to check
	compatibility

	Z80 bits
	0:	Z80 illegals
	1:	Z180
	2:	Z280
	3:	R800

	6809 bits
	0:	6309

	8086 bits
	0:	8087
	1:	801C86 instructions (push immediate etc)
	2:	80286
	3:	80287

	68000 bits
	0:	68010
	1:	68020
	2:	68030
	3:	68040
	4:	68060
	5:	FPU	(might need 2 bits of FPU info)

	68HC11
	None needed I believe

	PDP/11	TBD



Proposed Relocation Format:
	
	1-255	skip 1-255 bytes and then add the high byte of the base
		to this address.
	0 0	end
	0 1-255	skip 1-255 bytes

6502/HC11 has a second set of entries that relocate ZP shifting the ZP offsets
by the ZP base of the platform

65C816 if we disallow swapping and support large mode will also need a 3rd
pass that updates banks from 0..n to the ones assigned



32bit

Uses binfmt_flat with tiny tweaks to avoid loading Linux binaries


Entry Conditions & System Calls

6502/65C816:
	C stack configured in zero page (unrelocated 0/1)
	6502 stack set to end of 6502 stack space (may not be $1FF)
	X holds high byte of load address
	A holds first zero page value allocated
	Y undefined

	Execution begins at first byte of loaded binary
	Signal vector helper code must be present at offset 20

	Need to sort out syscall vector and relocations for it (maybe
	pass it in Y ?)

	System calls via jmp ($00fe) [to be fixed for relocation etc]
	Arguments on C stack (ZP:0 + base)
	X holds the syscall number
	Y holds the number of arguments

	Behaves like a cc65 non fast call, so the syscall unstacks the
	passed arguments

	Returns in YX with error code in A and Z clear if no error

68000:
	A7 is set to the C stack
	Code is always relocated
	Other registers are undefined

	System calls:

	32bit pointer / 32bit int unlike smaller ports

	trap 15 causes a SIGTRAP

	trap14 (currently - may relocate this)
	d0 = syscall
	d1 = arg1
	a0 = arg2
	a1 = arg3
	a2 = arg4

	The only register we guarantee to save is A5, thus anything using
	base relative addressing needs to use A5 as the base because signal
	handling at the wrong moment may mean all other registers are
	undefined. This might seem a pain but it saves us a load of clocks!

	return value is in d0.l and a0.l (for convenience)
	error code is in d1.w

6809:
	S is set to the C stack
	X holds the load address
	other registers undefined

	Execution begins at first byte of loaded binary
	No signal vector helper required

	System calls are via swi
	Arguments on the caller stack, call number in D when swi
	Caller unstacks

	Returns error code in D, return in X

Z80:
	SP is set to the C stack
	IY holds the base address (load for relocatables)
	HL holds the load address

	System calls:
	Alternate registers are saved

	On entry userspace stack holds the syscall arguments
	On return HL holds the return value and carry is clear
	On error return HL holds the error and carry is set