Actually in this specific case there is a simple solution. Compare how is it done in examples/x86/include/8086.inc:
macro x86.short_jump opcode,dest
x86.parse_jump_operand @dest,dest
if @dest.type = 'imm' & ( @dest.jump_type = 'short' | ~ @dest.jump_type )
if @dest.imm relativeto 0 & (@dest.imm < 0 | @dest.imm >= 10000h)
err 'value out of range'
end if
db opcode
if @dest.imm-($+1)<80h & @dest.imm-($+1)>=-80h
db @dest.imm-($+1)
else
err 'relative jump out of range'
db ?
end if
else
err 'invalid operand'
end if
end macro All that you need is to ensure that the offsets remain stable no matter if condition is fulfilled, so even in case of error generate the fields of appropriate length:
macro jz? dest*
local addr
addr = dest - $ - 2
db 01110100b
if addr >= -128 & addr < 128
db addr
else
err asmerr_jmp__outof_range
db ?
end if
end macro
NNN = 128
lbl_a:
db 6
jz lbl_a
jz lbl_b
db NNN dup 0
lbl_b: Your problem was caused originally by the fact that when the relative offset was out of range, no bytes for instruction opcode were generated and therefore the relative offset shortened, leading to contradiction. You could read that statement as "if this block of code is longer than X, this instruction is not generated". When not generating an instruction causes the block to be shorter than X, that statement becomes contradictory.
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> Compiler Internals > [fasmg] Cannot generate code for jz macro
01 Mar 2017, 16:42