Cherry-pick standalone Fuchsia/Zircon Emulator/QEMU from the Fuchsia build environment

[elliott10]

A Standalone Fuchsia Emulator

After compiling a complete Fuchsia OS, we can execute the following commands to run the native emulator FEMU :
cd $FUCHSIA_DIR
fx emu -N
But this way we don't know what FEMU is actually doing, and we can't run FEMU outside the Fuchsia build environment.

So I picked out these files and directories FEMU needs. And organized into LIST A below.
Copy the Fuchsia files and directories in LIST A to LinuxOS without Fuchsia build environment. Keep the directory structure.

Setup network:
sudo ip tuntap add dev qemu mode tap user $USER
sudo ifconfig qemu up

Then run Fuchsia Emulator(FEMU) with ssh access:

tools/devshell/emu -N

You can also add parameters to accelerate graphic:
--host-gpu , using the host GPU
--software-gpu ,software rendering using SwiftShader

prebuilt/third_party/aemu/linux-x64/emulator will be called. See the detailed operating parameters:

fuchsia/prebuilt/third_party/aemu/linux-x64/emulator -feature VirtioInput,GLDirectMem,KVM,Vulkan -window-size 1280x800 -gpu auto -fuchsia -kernel fuchsia/out/default/multiboot.bin -initrd /tmp/tmp.eu8Jd9nVUm/fuchsia-ssh.zbi -m 8192 -serial stdio -vga none -device virtio-keyboard-pci -device virtio_input_multi_touch_pci_1 -smp 4,threads=2 -machine q35 -device isa-debug-exit,iobase=0xf4,iosize=0x04 -enable-kvm -cpu host,migratable=no,+invtsc -netdev type=tap,ifname=qemu,id=net0,script=no -device e1000,netdev=net0,mac=52:54:00:63:5e:7a -drive file=/tmp/tmp.eu8Jd9nVUm/fvm.blk,format=raw,if=none,id=vdisk -device virtio-blk-pci,drive=vdisk -append 'TERM=xterm-256color kernel.serial=legacy kernel.entropy-mixin=14260cdcbbc4515f507ec9f9a6294b81ea2b331365e06d764daa7ff48cdcf0c7 kernel.halt-on-panic=true '

Run&Debug Zircon under QEMU

Normally, the following command can run the Fuchsia QEMU:
fx qemu -- -s

Alternatively, We can construct a QEMU excution environment for Zircon.
Add these files and directories in LIST B below. Keep the directory structure.
Run the following command to be able to attach with GDB later:

tools/devshell/qemu -- -s

fuchsia/prebuilt/third_party/qemu/linux-x64/bin/qemu-system-x86_64 will be called.
The detailed QEMU operating parameters:

fuchsia/prebuilt/third_party/qemu/linux-x64/bin/qemu-system-x86_64 -kernel fuchsia/out/default/multiboot.bin -initrd fuchsia/out/default/tmp.8yN/fuchsia-ssh.zbi -m 8192 -nographic -drive file=fuchsia/out/default/tmp.8yN/fvm.blk,format=raw,if=none,id=mydisk -device ich9-ahci,id=ahci -device ide-drive,drive=mydisk,bus=ahci.0 -nic none -smp 4,threads=2 -machine q35 -device isa-debug-exit,iobase=0xf4,iosize=0x04 -fw_cfg name=etc/sercon-port,string=0 -cpu Haswell,+smap,-check,-fsgsbase -append 'TERM=xterm-256color kernel.serial=legacy kernel.entropy-mixin=cb8755a857c99d8ac8308220fe065a0904d6b660a8dcbfacdb7870cf91115abb kernel.halt-on-panic=true ' -s

According to the detailed QEMU operating parameters, we can manually generate the required files.
Generate initrd file and drive file:
fuchsia/out/default.zircon/tools/zbi --compressed=zstd -o ./fuchsia-ssh.zbi fuchsia/out/default/fuchsia.zbi --entry data/ssh/authorized_keys=fuchsia/.ssh/authorized_keys

source fuchsia/tools/devshell/lib/fvm.sh HOST_OUT_DIR=$PWD/fuchsia/out/default/host_x64 fx-fvm-extend-image fuchsia/out/default/obj/build/images/fvm.blk ./fvm.blk

At this time we can manually modify the QEMU parameters. For example, to replace kernel or file system.
fuchsia/prebuilt/third_party/qemu/linux-x64/bin/qemu-system-x86_64 -kernel fuchsia/out/default.zircon/multiboot.bin -initrd ./fuchsia-ssh.zbi -m 2G -display none -drive file=./fvm.blk,format=raw,if=none,id=mydisk -device ich9-ahci,id=ahci -device ide-drive,drive=mydisk,bus=ahci.0 -serial stdio -append 'kernel.serial=legacy kernel.halt-on-panic=true ' -s

Now we can debug the kernel with "-s" parameter.

gdb out/default.zircon/kernel-x64-clang/obj/kernel/zircon.elf -x ./out/default.zircon/kernel-x64-clang/obj/kernel/zircon.elf-gdb.py
(gdb) target extended-remote :1234
(gdb) break lk_main
(gdb) continue
^C
(gdb) info threads

zircon.elf-gdb.py is gdb's Zircon debugging script.

---

LIST A for FEMU

tools/devshell/
./.fx-build-dir
./.config
./.ssh/authorized_keys
prebuilt/third_party/aemu/linux-x64/
prebuilt/third_party/grpcwebproxy/linux-x64/

out/default/rust-project.json
out/default/fx.config
out/default/args.gn

out/default/fuchsia.zbi
out/default/fuchsia.zbi
out/default/zedboot.zbi
out/default/zedboot.zbi
out/default/fuchsia.esp.blk
out/default/obj/build/images/blob.blk
out/default/obj/build/images/data.blk
out/default/obj/build/images/fvm.blk
out/default/obj/build/images/fvm.sparse.blk
out/default/obj/build/images/fvm.blob.sparse.blk
out/default/multiboot.bin
out/default/zedboot.esp.blk
out/default/netboot.zbi
out/default/netboot.zbi

out/default/host-tools/device-finder
out/default/host_x64/fvm

out/default.zircon/tools/

LIST B for Zircon using QEMU

/zircon/scripts/
prebuilt/third_party/qemu/linux-x64/
out/default.zircon/multiboot.bin
out/default.zircon/kernel-x64-clang/obj/kernel/zircon.elf
out/default.zircon/kernel-x64-clang/obj/kernel/zircon.elf-gdb.py