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The costs of the i386 to x86-64 upgrade

If you read my previous article on DOS memory models, you may have dismissed everything I wrote as “legacy cruft from the 1990s that nobody cares about any longer”.  It's time to see how any of that carried over through the 16-bit to 64-bit evolution.

Unfortunately, running a broader comparison than this is difficult: there is no full operating system I can find that ships both builds any longer, and ARM images can’t easily be compared. Consider this: we could have made the operating system kernel leverage 64 bits to gain access to a humongous address space, but we could have kept the user-space programming model as it was before—that is, we could have kept ILP32. Now, the main method of our hello-world program is really similar between the 64-bit and 32-bit builds, but pay close attention to the x32 version: it uses the same calling conventions as x86-64, but it contains a mixture of 32-bit and 64-bit registers, delivering a more compact binary size.

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