Disassembly with variable instruction size

[Ronald Hecht <ronald dot hecht at uni-rostock dot de>]

Hello,

I'm porting a very simple architecture for educational purposes. I got 
gas working, but the dissasemble with objdump not. It is an 8 bit 
processor with variable instruction size. The first byte is the opcode 
the second an 8 bit immediate or together with the third byte an 16 bit 
immediate. The disassemble of the "make gas-test" looks very strange, 
whereas the object file is correct.

I played with "lsb0". As I saw in the mailing list there are problems 
with #t. So I decided to use #f.

Attached is the cpu file, the assemble, disasemble, and the object file.

Thanks in advance
Ronald


; Simple 8 Bit Processor -*- Scheme -*-

(include "simplify.inc")

; FIXME: Delete sign extension of accumulator results.
; Sign extension is done when accumulator is read.

; define-arch must appear first

(define-arch
  (name proc) ; name of cpu family
  (comment "8 Bit Processor")
  (insn-lsb0? #f)
  (machs proc)
  (isas proc)
)

(define-isa
  (name proc)
  (default-insn-bitsize 8)
  (base-insn-bitsize 8)
  (default-insn-word-bitsize 8)
)

(define-cpu
  (name proc)
  (comment "8 Bit Processor Family")
  (endian big)
  (word-bitsize 8)
)

(define-mach
  (name proc)
  (comment "8 Bit FPGA Processor")
  (cpu proc)
)

(define-model
  (name proc)
  (comment "8 Bit Processor Model")
  (attrs)
  (mach proc)
  (unit u-exec "Execution Unit" () 1 1
	() () () ())
)

(dnf f-op        "op"                        ()   0  8)
(dnf f-uimm8     "unsigned 8 bit immediate"  ()   8  8)
(dnf f-uimm16    "unsigned 16 bit immediate" ()   8 16)

(define-normal-insn-enum
  insn-op "insn format enums" () OP_ f-op
  (.map .str (.iota 256))
)

(dnh h-pc "program counter" (PC PROFILE) (pc) () () ())

(define-hardware
  (name h-accu)
  (comment "Accumulator")
  (attrs PROFILE );CACHE-ADDR)
  (type register DI )
)

(define-attr
  (for operand)
  (type boolean)
  (name HASH-PREFIX)
  (comment "immediates have an optional '#' prefix")
)

(dnop accu     "accumulator"               () h-accu   f-nil)
(dnop uimm8    "unsigned 8 bit immediate"  () h-uint   f-uimm8)
(dnop uimm16   "unsigned 16 bit immediate" () h-uint   f-uimm16)


(dni nop "nop"
     ()
     "nop"
     (+ OP_0)
     (nop)
     ()
)

(dni lda "lda"
     ()
     "lda $uimm16"
     (+ OP_1 uimm16)
     (set accu (mem WI uimm16))
     ()
)

(dni ldc "ldc"
     ()
     "ldc $uimm8"
     (+ OP_2 uimm8)
     (set accu uimm8)
     ()
)

(dni decx "decx"
     ()
     "decx"
     (+ OP_100)
     (nop)
     ()
)

(dni decy "decy"
     ()
     "decy"
     (+ OP_101)
     (nop)
     ()
)

#as:
#objdump: -dr
#name: allinsn

*: +file format .*

Disassembly of section \.text:

00000000 <nop>:
	\.\.\.

00000001 <lda>:
   1:	01 00       	 -> lda 0x100
   3:	00 01       	 -> nop
   5:	ff ff       	 || \*unknown\*
   7:	01 80       	 -> lda 0xffff
   9:	00 01       	 -> nop
   b:	7f ff       	 -> \*unknown\*
   d:	01 00       	 -> lda 0x100
   f:	01 01       	 -> lda 0x100
  11:	c5 bd       	 || \*unknown\*
  13:	01 fa       	 -> lda 0xc5bd
  15:	6d 01       	 -> \*unknown\*
  17:	5e 51       	 -> \*unknown\*

00000019 <ldc>:
  19:	02 00       	 -> ldc 0x2
  1b:	02 ff       	 -> ldc 0x2
  1d:	02 80       	 -> ldc 0x2
  1f:	02 7f       	 -> ldc 0x2
  21:	02 01       	 -> ldc 0x2
  23:	02 f7       	 -> ldc 0x2
  25:	02 54       	 -> ldc 0x2
  27:	02 ea       	 -> ldc 0x2

00000029 <decx>:
  29:	64 65       	 -> decx

0000002a <decy>:
  2a:	65 00       	 -> decy

 .data
foodata: .word 42
 .text
footext:
	.text
	.global nop
nop:
	nop
	.text
	.global lda
lda:
	lda 0
	lda 65535
	lda 32768
	lda 32767
	lda 1
	lda 50621
	lda 64109
	lda 24145
	.text
	.global ldc
ldc:
	ldc 0
	ldc 255
	ldc 128
	ldc 127
	ldc 1
	ldc 247
	ldc 84
	ldc 234
	.text
	.global decx
decx:
	decx
	.text
	.global decy
decy:
	decy

Attachment: a.out
Description: Binary data