IDA API: obtain operand size prefix (x64)

Question

I am trying to tell apart the following two instructions:

8D 02      lea     eax, [rdx]  // auxfix = 0x1810
67 8D 02   lea     eax, [edx]  // auxfix = 0x810

The only difference is in the insn_t.auxfix field, which seems to hold some operand size flag related to modr/m.

As you can see bit 1 << 12 seems to tell me something ... but how exactly can I interpret this field for x86 and x64?

Answer 1

Open up intel.hpp that ships with the SDK. The aux prefix flags are defined at the top; the one you're interested in is as follows:

#define aux_natad       0x00001000  // addressing mode is not overridden by prefix