Big-Endian Testing with QEMU

I wrote a similar post [1] some 16 years ago. My solution back then was to install Debian for PowerPC on QEMU using qemu-system-ppc.

But Hans's post uses user-mode emulation with qemu-mips, which avoids having to set up a whole big-endian system in QEMU. It is a very interesting approach I was unaware of. I'm pretty sure qemu-mips was available back in 2010, but I'm not sure if the gcc-mips-linux-gnu cross-compiler was readily available back then. I suspect my PPC-based solution might have been the only convenient way to solve this problem at the time.

Thanks for sharing it here. It was nice to go down memory lane and also learn a new way to solve the same problem.

[1] https://susam.net/big-endian-on-little-endian.html

What I really want is memory order emulation. X86 as strong memory order guarantees, ARM has much weaker guarantees. Which means the multi-threaded queue I'm working on works all the time on development x86 machine even if I forget to put in the correct memory-order schematics, but it might or might not work on ARM (which is what my of my users have). (I am in the habit of running all my stress tests 1000 times before I'm willing to send them out, but that doesn't mean the code is correct, it means it works on x86 and passed my review which might miss something)

> When programming, it is still important to write code that runs correctly on systems with either byte order

What you should do instead is write all your code so it is little-endian only, as the only relevant big-endian architecture is s390x, and if someone wants to run your code on s390x, they can afford a support contract.

If you're using Go on GitHub (and doing stuff where this actually matters) adding this to your CI can be as simple as this: https://github.com/ncruces/wasm2go/blob/v0.3.0/.github/workf...

On Linux it's really as simple as installing QEMU binfmt and doing:

   GOARCH=s390x go test

> When programming, it is still important to write code that runs correctly on systems with either byte order

I contend it's almost never important and almost nobody writing user software should bother with this. Certainly, people who didn't already know they needed big-endian should not start caring now because they read an article online. There are countless rare machines that your code doesn't run on--what's so special about big endian? The world is little endian now. Big endian chips aren't coming back. You are spending your own time on an effort that will never pay off. If big endian is really needed, IBM will pay you to write the s390x port and they will provide the machine.

For most code it doesn't matter. It matters when you are writing files to be read by something else, or when sending data over a network. So make sure the places where those happen are thin shims that are easy to fix if it doesn't work. (that is done write data from everywhere, put a layer in place for this).

I did that many years back, but with MIPS and MIPSel: https://youtu.be/BGzJp1ybpHo?si=eY_Br8BalYzKPJMG&t=1130

presented at Embedded Linux Conf

Is there any benefit in edge cases to using big-endian these days?

It's all fun and games until you have to figure out if the endianness bug is in your code or in QEMU's s390x emulation.