Visual Studio .NET 2005 Training Tutorial 64 Bit vs 32 Bit: When targeting x64 platforms in Visual Studio .NET 2005, programmers are no longer able to use inline assembly code as they did for 32-bit code. This forces the programmer to either rely on C/C++ code using intrinsics, or to tediously create a 64-bit MASM (.asm) version of the function.

---

by Eric Palmer

When targeting x64 platforms in Visual Studio .NET* 2005, programmers are no longer able to use inline assembly code as they did for 32-bit code. This forces the programmer to either rely on C/C++ code using intrinsics, or to tediously create a 64-bit MASM (.asm) version of the function. Unfortunately, the VS .Net 2005 implementation of the intrinsic for CPUID (__cpuid) recognizes only input arguments in the register eax, and not the more recently defined inputs in ecx, which are required for queries regarding cache parameters and certain multi-core characteristics. Thus, a 64-bit .asm listing is required for full use of the CPUID instruction.

The following code samples demonstrate how to use the CPUID and RDTSC instructions with VS .Net 2005 for 64-bit (x64) platforms. The CPUID instruction is commonly used to obtain detailed information about the system’s CPU(s), and RDTSC is used to read the CPU’s internal time-stamp counter for timing and performance-measurement purposes. The RDTSC intrinsic (__rdtsc) does work as expected and can be used to replace inline assembly.