QEMU issues with 32-bit applications and floating math

[arekkusu42]

As discussed in #5371 and #4990 QEMU 7.2 introduced a TCG regression which:

• causes some guest OS (macOS El Capitan, at least) to crash during login
• causes some guest applications (any 32-bit GUI app in macOS Mavericks or later) to crash
• potentially crashes ANY macOS application using float math

Until this is resolved, I suggest rolling UTM's QEMU back to 7.1.

I can not find an open QEMU bug tracking this, so possibly they are unaware. The root cause is probably this commit, but I have not debugged it to confirm. It also looks like the TCG i386 emulator has seen many changes after 7.2, so before filing a new bug someone needs to reproduce the problem with a current QEMU release or TOT.

Minimal reproducers are here.

[osy]

We plan to update QEMU to the latest version in the next release. Do you know if it's fixed upstream?

[arekkusu42]

I do not know; QEMU does not provide Mac binaries, and I do not currently have a build environment to build/test/debug it.

Reviewing the TCG commits I do not see any obvious fix, so I suspect the problem is still there, but as I mentioned, someone needs to reproduce with QEMU TOT. If a new UTM beta with updated QEMU is released before I set up a build environment, I can test it that way.

(updating QEMU should fix this annoying assertion though, so that'd be nice.)

[osy]

You can use brew install qemu if you need macOS binaries

[arekkusu42]

If you come from Linux, this may seem normal, but brew is... very far from what I would call "providing Mac binaries". On a Mac, downloading a .dmg and double-clicking the app does not require:

• installing anything (/opt/local, the Xcode dev tools, etc)
• installing anything (thousands of redundant-but-slightly-different dependancies)
• installing anything (the app itself can run from the compressed .dmg)
• giving sudo permission to install anything
• opting in to analytics by default

Anyhow... I did set up homebrew (in a Sonoma VM, thank you UTM!) and it installed qemu 8.2.1 (so I can't speak to the 9.0rc or TOT). Then, after copying VMs around and cobbling together invocations, I verified that the three minimal reproducers do NOT crash, in Mavericks or Sierra. I was able to run my ancient (compiled as i386) emulators, inside the qemu-system-x86_64 emulator, inside the UTM arm64-virtualized-on-arm64 Sonoma. Woot.

So, that means that TCG looks fixed, circa QEMU 8.2.1? I guess you should go ahead and update in the next release, and we'll see if anything else in the UTM build causes problems.