[Bug 1882123] Re: ARM cpu emulation regression on QEMU 4.2.0

[Hajin Jang]

I pinpointed the exact commits which affected the regression.

[QEMU 4.2.0-rc0 : illegal hardware instruction]
- Introduced in commit af28822
https://github.com/qemu/qemu/commit/af2882289951e58363d714afd16f80050685fa29
The commit affected LDREX/STREX translation, and broke dotnet command from .NET 
Core SDK.

[QEMU 4.2.0-rc2 : .NET SEHException]
- Introduced in commit 655b026
https://github.com/qemu/qemu/commit/655b02646dc175dc10666459b0a1e4346fc8d46a
The commit fixes STREX a bit. As a result, dotnet command is now executable 
except JIT compiling. 


I also tested lastest HEAD from the master, and it still has the SEHException 
regression.
(Tested commit is 66234fee9c2d37bfbc523aa8d0ae5300a14cc10e)

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https://bugs.launchpad.net/bugs/1882123

Title:
  ARM cpu emulation regression on QEMU 4.2.0

Status in QEMU:
  New

Bug description:
  [*] Summary

  Latest QEMU has an ARM CPU emulation regression.
  Regression is reproducible by building any C# project with .NET Core SDK 
3.1.300 on Debian 10 armhf guest OS.

  Releases affected: QEMU 4.2.0, 5.0.0
  Releases not affected: QEMU 4.1.0, QEMU 4.1.1

  [*] Detail

  .NET Core SDK 3.1 fails to run on Debian 10 emulated by qemu-system-
  arm.

  I occasionally test my C# projects on the virtual armhf/arm64 system
  emulated by QEMU. MSBuild, a build engine of the .NET Core SDK,
  crashes on QEMU 4.2.0 or later. The crash only happens when MSBuild
  tries to do any JIT compiling (dotnet build / dotnet test).

  I attached the MSBuild crash logs. MSBuild always crashes with
  SEHException, which means it tried to call C binary from .NET binary.

  I think the ARM CPU emulation regression happened between QEMU 4.1.1 ~
  4.2.0. The issue affects QEMU 4.2.0 and 5.0.0. QEMU 4.1.0, 4.1.1, and
  real Raspberry Pi 2 are not affected by this issue, and .NET Core SDK
  works completely fine.

  [*] Environment

  [Host OS]
  Distribution: Linux Mint 19.3 amd64
  CPU: AMD Ryzen 5 3600
  Kernel: Ubuntu 5.3.0-51-generic

  [QEMU Guest OS]
  Distribution: Debian 10 Buster armhf
  Kernel: Debian 4.19.0-9-armmp-lpae
  .NET Core SDK: 3.1.300

  [Raspberry Pi 2]
  Distribution: Raspberry Pi OS Buster armhf
  Kernel: 4.19.118-v7+

  [Tested C# Projects]
  This is a list of C# projects I have tested on QEMU and RPI2.
  - https://github.com/ied206/Joveler.DynLoader
  - https://github.com/ied206/Joveler.Compression
  - https://github.com/ied206/ManagedWimLib

  [QEMU Launch Arguments]
  qemu-system-arm \
      -smp 3 -M virt -m 4096 \
      -kernel vmlinuz-4.19.0-9-armmp-lpae \
      -initrd initrd.img-4.19.0-9-armmp-lpae \
      -append "root=/dev/vda2" \
      -drive if=none,file=debian_arm.qcow2,format=qcow2,id=hd \
      -device virtio-blk-device,drive=hd \
      -netdev user,id=mynet,hostfwd=tcp::<PORT>-:22 \
      -device virtio-net-device,netdev=mynet \
      -device virtio-rng-device

  [QEMU Configure Arguments]
  ./configure --enable-spice --enable-gtk --enable-vnc-jpeg --enable-vnc-png 
--enable-avx2 --enable-libusb --enable-opengl --enable-virglrenderer 
--enable-kvm --enable-system --enable-modules --audio-drv-list=pa

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