(rephrased to better match sleigh terminology)

I'm working on a processor description for VAX and would need to get the address of an instruction operand.

VAX has one-byte opcodes followed by operands with variable (1 to 5 bytes) length.

Examples (not exact mnemonics)

1. one-byte opcode, two one-byte operands

00000000: 90 01 50 - MOVE.B S^1, R0

2. one-byte opcode, one two-byte operand, one four-byte operand

00000000: 90 CF 34 12 E0 78 56 34 12 - MOVE.B (PC+0x1234), (R0 + 0x12345678)

Example 2 is the problem. The first operand ("CF 34 12") is PC-relative, it computes PC+0x1234, where PC is right after the final "12" value. In the example above, that would result in 0x1238.

Problem

To compute PC-relative offsets correctly, I need to know the operands memory address. However, neither inst_start, nor inst_next are usable here:

• I can't use inst_start because the operand might be second and I don't know the size of the first operand.

• I can't use inst_next because the operand might be first and I don't know the size of the second operand.

Are there any other options ?