It is a simple debugger log in the transputer emulator (enabled by compilation option) which outputs each instruction executed so far, around 70 bytes per line displaying the 3 registers, the stack pointer, the instruction pointer, and the disassembled instruction.

The emulated C compiler processed a whole file ccvars.c before getting stuck in ccinter.c (this is the 5gb mark, approximately 78 millions of instructions executed). I stopped the process as soon as I saw it was stuck, but the emulator is fast, and I got extra 3 gb in the log. All this happened in less than two minutes.