On 2020-11-10 at 13:58:21, Johannes Schindelin wrote: > The biggest question now is: are we certain that `_M_ARM64` implies > little-endian? For Windows? Yes. I'm almost certain Windows has only supported little-endian architectures, possibly with the exception of gaming consoles. > I remember that ARM (the 32-bit variety, that is) has support for > switching endianness on the fly. Happily, MSVC talks specifically about > _not_ supporting that: > https://docs.microsoft.com/en-us/cpp/build/overview-of-arm-abi-conventions > > Likewise, it says the same about ARM64 (mentioning that it would be much > harder to switch endianness there to begin with): > https://docs.microsoft.com/en-us/cpp/build/arm64-windows-abi-conventions > > So does that make us confident that we can just add that `_M_ARM64` part? > Yes. Does it make me confident that we can just drop all of the > architecture-dependent conditions? No, it does not. There _were_ versions > of MSVC that could compile code for PowerPC, for example, which _is_ > big-endian. PowerPC can actually be either. Most 64-bit PowerPC machines these days are run as little endian, and Windows has always run it in little-endian mode. Macs ran it in big-endian mode. > > As far as I know, Windows has always run on little-endian hardware. > > I think that depends on your point of view... IIRC an early version of > Windows NT (or was it still VMS Plus?) ran on DEC Alpha, which I seem to > _vaguely_ remember was big-endian. Alpha appears to have supported both, but as far as I know, both Windows and Linux used it in little-endian mode. > > [0] Wikipedia does not specify the endiannesses supported by the MIPS > > edition. > > I have another vague memory about MIPS (a wonderful SGI machine I had the > pleasure of banging my head against, for lack of Python support and Git > requiring Python back then) being big-endian, too. Another architecture that supports both endiannesses. Debian supports both, but I believe Windows only supported the little-endian version. I have a small MIPS board that uses the little endian port for Debian. > Short version: while I managed to convince myself that _currently_ there > are no big-endian platforms that we can support via MSVC, I would like to > stay within the boundaries of caution and _not_ drop those `defined(_M_*)` > parts. While I'm confident in my statements, you're the relevant subsystem maintainer here, so I'm happy to defer to your judgment. I think Junio can just pick up the earlier patch version and we should be good to go, since that patch seemed to meet everyone's needs. -- brian m. carlson (he/him or they/them) Houston, Texas, US
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