Trap guestOS to run SDL-oriented applications

[ChinYikMing]

To trap the guest OS SDL applications, virtual memory translation should be handled when accessing the bidirectional event queues in syscall_sdl.c. Additionally, when using the guest OS, the SDL application might be launched and terminated multiple times. To enhance the user experience, it is heuristic to properly handle three main types of exits:
1, SDL application built-in exit: The source code of the SDL application should be modified to call the syscall_exit(syscall number: 93) somewhere when executing cleanup routine before exit().
2. Ctrl-c (SIGINT) exit: Detect the ctrl-c keycode.
3. SDL window Quit event: The source code of the SDL application should be modified to call the syscall_exit(syscall number: 93) when receiving SDL window Quit event.

The main reason for handling these three types of exits is that SDL2_Mixer may malfunction if not properly initialized and destroyed, as it runs on the host side not on the guest side. Additionally, when terminating an SDL application in the guest OS, the previous SDL window should be closed.

Moreover, the default audio backend of SDL2_Mixer(downloadable from brew or Linux distro pkg managers), FluidSynth, occasionally generates the warning: "fluidsynth: warning: Ringbuffer full, try increasing synth.polyphony!" This issue causes the audio to hang, leading to an unstable playback experience. Thus, dropping FluidSynth in favor of the Timidity backend, which provides a stable audio playback experience.

Known issue: Calling SDL_DestroyWindow() on macOS does not close the previous SDL window.

Close: #510

Note that the following steps are conducted on Ubuntu 22.04 x86-64 machine

Build SDL2_Mixer from source

1. Download https://github.com/libsdl-org/SDL_mixer and checkout to commit de7b2f4d2a7e78db363cb26a66df4da1f9524e25

2. Disable FluidSynth

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -110,7 +110,7 @@ endif()
 
 option(SDL2MIXER_MIDI "Enable MIDI music" ON)
 
-cmake_dependent_option(SDL2MIXER_MIDI_FLUIDSYNTH "Support FluidSynth MIDI output" ON "SDL2MIXER_MIDI;NOT SDL2MIXER_VENDORED" OFF)
+cmake_dependent_option(SDL2MIXER_MIDI_FLUIDSYNTH "Support FluidSynth MIDI output" OFF "SDL2MIXER_MIDI;NOT SDL2MIXER_VENDORED" OFF)
 cmake_dependent_option(SDL2MIXER_MIDI_FLUIDSYNTH_SHARED "Dynamically load libfluidsynth" "${SDL2MIXER_DEPS_SHARED}" SDL2MIXER_MIDI_FLUIDSYNTH OFF)
 
 if(WIN32 OR APPLE OR HAIKU)

3. Build (note that this will override the pre-installed SDL2_Mixer)
   Might need to install some dependency library(see the error logs if it shows)

$ mkdir -p build && cd build && cmake .. -DCMAKE_INSTALL_PREFIX=/usr -DCMAKE_INSTALL_INCLUDEDIR=include && make -j$(nproc) && sudo make install 

4. Download timidity's GUS patches which from the README of SDL2_Mixer.
5. Extract timidity/* into /etc/ directory.

Testing procedure

1. Unzip Image.zip and rootfs.cpio.zip to desired path.
   Image.zip
   rootfs.cpio.zip

2. Build rv32emu

$ make INITRD_SIZE=64 ENABLE_SYSTEM=1 ENABLE_SDL=1 -j$(nproc)

3. Run rv32emu with provided Image and rootfs.cpio

$ build/rv32emu -k <kernel_img_path> -i <rootfs_img_path>

4. Run SDL-oriented application in guestOS (doom-riscv or quake or smolnes)

# doom-riscv

Expectation

Three SDL-oriented applications should be runable and can be exited with all three types of exits without any crash.

Update: (SDL2_mixer build from source on macOS/arm64)

The 1, 2, 4, 5 steps are same to Linux host, but a tiny change to step 3:
3. Build (note that this will override the pre-installed SDL2_Mixer)
Might need to install some dependency library(see the error logs if it shows)

$ mkdir -p build && cd build && cmake .. -DCMAKE_INSTALL_PREFIX=/opt/homebrew -DCMAKE_INSTALL_INCLUDEDIR=include && make -j$(sysctl -n hw.logicalcpu) && sudo make install 

[jserv]

Benchmarks

Benchmark suite	Current: f20b959	Previous: 515e011	Ratio
Dhrystone	1324 Average DMIPS over 10 runs	1306 Average DMIPS over 10 runs	0.99
Coremark	961.974 Average iterations/sec over 10 runs	963.25 Average iterations/sec over 10 runs	1.00

This comment was automatically generated by workflow using github-action-benchmark.

[ChinYikMing]

Once this merged, I will upload more compact rootfs.cpio to rv32emu-prebuilt.

[jserv]

Thank @ChinYikMing for contributing!