4.1.3 Maximize Warning Levels

To catch possible issues with assigning or comparing values of different sizes, UEFI drivers should always be compiled with the highest warning level possible. For example, the Microsoft* compilers support the /WX and /W3 or /W4 compiler flags. The /WX flag causes any compile time warnings to generate an error, so the build stops when a warning is generated. The /W3 and /W4 flags set the warning level to 3 and 4 respectively. At these warning levels, any size mismatches in assignments and comparisons generate a warning. With the /WX flag, the compile stops when such size mismatches are detected.
If a UEFI Driver is being developed for a 32-bit architecture and is expected to be ported to a 64-bit architecture, it is a good idea to compile the UEFI driver with a 64bit compiler during the development process. This helps ensure the code is clean when validation on the 64-bit processor is begun. By using the /WX and /W3 or /W4 compiler flags, any size mismatches that are generated by only 64-bit code are detected.
TIP: As the warning levels are increased, a compiler may produce more error messages. This helps develop more robust, portable code.