What is all the TBEMD stuff

I've been getting questions about what TBEMD means in my commits to FreeBSD head.

First, I'll tell you the name. TBE stands for TARGET_BIG_ENDIAN. For the MIPS and ARM ports, it is an environment variable that you have to set to build these targets for big endian (otherwise they default to little endian). MD is Must Die. A few years ago, there was an action movie whose title was more memorable than the file "Romeo Must Die." So I just stole the name for this branch.

So why must TARGET_BIG_ENDIAN die? It breaks things. For all the other platforms that FreeBSD supports, you just set TARGET and/or TARGET_ARCH to do cross builds. You know everything you need to know from the MACHINE and MACHINE_ARCH in the resulting image. In addition, the build system segregates things so you can build all the targets in one tree..But for mips and arm, you don't know what endian a binary is, the obj tree will collide if you try to build both little endian and big endian binaries at the same time. There's also other, more subtle issues. For example, TARGET_BIG_ENDIAN isn't set on big endian mips, so a native biuldworld tries to build little endian binaries (oops).

So, mips will be moving to mipsel (for little endian) and mipseb (for big endian). Arm will move to arm (for little endian) and armeb (for big endian). You could fill an entire email archive with all the possible other names and why they are better or worse than these names. History, however, trumps all those arguments: these are the names used elsewhere and we're just following convention.

Once tbemd is completely merged, you'll be able to build both endians of MIPS in the same object tree, for example, and all the other issues I've discovered. It also helps with new architectures as we move into powerpc64 (already merged) and mips64 (to be done after tbemd is collapsed). It will also mean we can have different packages for the different endians now.