I have two computers, the value of environment variable on different computer is not the same. For example, TMP is set to "C:\tmp" on compute 1, and TMP is set to "D:\Temp_Dir" on computer 2.
UD2 is a 2-byte undefined instruction. INT3 is interrupt 3 - trap to debugger. It is a single byte, 0xcc.
For indirect branches, Intel recommends: