Compiling

In order to get the x264 encoder to build with CUDA, it was necessary to modify Makefile.

These changes include:

• • list of .cu files to be built

  • link in the object files generated by nvcc (I called them .cuo)

  • Include cuda.mk

cuda.mk is likely overly complicated. It can be cleaned up. In order to do so we understand the compiler flags that are passed to nvcc.

• • use_fast_math?

Structs with long long

When compiling with GCC, special care must be taken for structs that contain 64-bit integers. This is because GCC aligns long longs to a 4 byte boundary by default, while NVCC aligns long longs to an 8 byte boundary by default. Thus, when using GCC to compile a file that has a struct/union, users must give the -malign-double option to GCC. When using NVCC, this option is automatically passed to GCC. (http://developer.download.nvidia.com/compute/cuda/2_0/docs/CUDA_Toolkit_Release_Notes_linux_2.0_08.pdf).

In other words we can solve the problem by passing -malign-double option to the GCC compiler.

I solved this problem by passing the following to the NVCC compiler:

TODOs:

• • Figure out if CUDA requires PIC. If so then figure out how this should be set (flag for linker, compiler, etc.; which flag -fPIC or -bSymbolic)

  • Eventually handle CUDA as an option in the configure script so that the Makefile will build the non-CUDA version. This is not important at this time but will be important if we are to merge our changes into the trunk.