Cpu: modify instructions' offset relative encoding

The assembler will automatically use instruction len in offset computation

In the following instruction:
0x10: EB 02   JMP 0x14

If we assemble this instruction, the requested instruction send to the assembler
engine will be:
JMP +0x4

And will be encoded to:
EB 02

Previously, the assembly of:
JMP +0x4
was:
EB 04

1 files changed, 16 insertions, 5 deletions

diff --git a/miasm2/arch/msp430/arch.py b/miasm2/arch/msp430/arch.py
index 07a11ae8..2cac7260 100644
--- a/miasm2/arch/msp430/arch.py
+++ b/miasm2/arch/msp430/arch.py
@@ -144,7 +144,7 @@ class instruction_msp430(instruction):
         if self.name == "call":
             ad = e.arg
         else:
-            ad = e.arg + int(self.offset) + self.l
+            ad = e.arg + int(self.offset)
 
         l = symbol_pool.getby_offset_create(ad)
         s = ExprId(l, e.size)
@@ -188,7 +188,11 @@ class instruction_msp430(instruction):
             # raise ValueError('dst must be int or label')
             log.warning('dynamic dst %r', e)
             return
-        self.args[0] = ExprInt_fromsize(16, (e.arg - (self.offset + self.l))/2)
+
+        # Call argument is an absolute offset
+        # Other offsets are relative to instruction offset
+        if self.name != "call":
+            self.args[0] =  ExprInt_fromsize(16, e.arg - self.offset)
 
     def get_info(self, c):
         pass
@@ -522,9 +526,16 @@ class msp430_offs(imm_noarg, m_arg):
         return ExprInt_fromsize(16, v)
 
     def decodeval(self, v):
-        return v << 1
+        v <<= 1
+        v += self.parent.l
+        return v
 
     def encodeval(self, v):
+        plen = self.parent.l + self.l
+        assert(plen % 8 == 0)
+        v -= plen / 8
+        if v % 2 != 0:
+            return False
         return v >> 1
 
     def decode(self, v):
@@ -574,8 +585,8 @@ bs_f2_nobw = bs_name(l=3, name={'swpb': 1, 'sxt': 3,
                                 'call': 5})
 addop("f2_2", [bs('000100'), bs_f2_nobw, bs('0'), a_s, sreg, off_s])
 
-
-offimm = bs(l=10, cls=(msp430_offs,), fname="offs")
+# Offset must be decoded in last position to have final instruction len
+offimm = bs(l=10, cls=(msp430_offs,), fname="offs", order=-1)
 
 bs_f2_jcc = bs_name(l=3, name={'jnz': 0, 'jz': 1, 'jnc': 2, 'jc': 3, 'jn': 4,
                                'jge': 5, 'jl': 6, 'jmp': 7})