In code example, the hexdump starts with B9 90 00 00 08, but in the disassembly is listed as 80 00 00 90. I don't think endianness can change 08 to 80.

there is no such predefined thing as STDOUT.

you are probably thinking of STDOUT_FILENO. can you just put "1" there?

also, reordering the "mov"s (so they appear in actual call order: edx, ecx, ebx) will simplify the diagram somewhat.