Zircon can run under emulation using QEMU. QEMU can either be installed via prebuilt binaries, or built locally.
QEMU is downloaded by jiri
as part of jiri update
or jiri run-hooks
.
QEMU is fetched into //prebuilt/third_party/qemu
. You can run it most conveniently using fx qemu
(see below).
Building QEMU on macOS requires a few packages. As of macOS 10.12.1:
# Using http://brew.sh brew install pkg-config glib automake libtool # Or use http://macports.org ("port install ...") or build manually
cd $SRC git clone --recursive https://fuchsia.googlesource.com/third_party/qemu cd qemu ./configure --target-list=aarch64-softmmu,x86_64-softmmu make -j32 sudo make install
If you don‘t want to install in /usr/local (the default), which will require you to be root, add --prefix=/path/to/install (perhaps $HOME/qemu). Then you’ll either need to add /path/to/install/bin to your PATH or use -q /path/to/install when invoking run-zircon-{arch}.
# for aarch64 fx set bringup.arm64 fx build fx qemu # for x86 fx set bringup.x64 fx build fx qemu
If QEMU is not on your path, use -q to specify its location.
The -h flag will list a number of options, including things like -b to rebuild first if necessary and -g to run with a graphical framebuffer.
To exit qemu, enter Ctrl-a x. Use Ctrl-a h to see other commands.
The run-zircon script, when given the -N argument will attempt to create a network interface using the Linux tun/tap network device named “qemu”. QEMU does not need to be run with any special privileges for this, but you need to create a persistent tun/tap device ahead of time (which does require you be root):
On Linux:
sudo ip tuntap add dev qemu mode tap user $USER sudo ip link set qemu up
This is sufficient to enable link local IPv6 (as the loglistener tool uses).
On macOS:
macOS does not support tun/tap devices out of the box; however, there is a widely used set of kernel extensions called tuntaposx, which can be downloaded here. Once the installer completes, the extensions will create up to 16 tun/tap devices. The run-zircon-x64 script uses /dev/tap0.
sudo chown $USER /dev/tap0 # Run zircon in QEMU, which will open /dev/tap0 fx qemu -N # (In a different window) bring up tap0 with a link local IPv6 address sudo ip addr add dev tap0 fc00::/7 sudo ip link set tap0 up
Using builds based on core (really any product above bringup) will automatically imply a disk that is provided to serve the fvm
partition that includes a minfs partition for mutable storage, and a blobfs partition for package data storage.
You can attach additional images using flags as follows:
fx qemu -d [-D <disk_image_path (default: "blk.bin")>]
Here is a sample session to get you started.
In the shell you're running QEMU in:
shell1$ fx qemu -- -s -S [... some QEMU start up text ...]
This will start QEMU but freeze the system at startup, waiting for you to resume it with “continue” in GDB. If you want to run QEMU without GDB, but be able to attach with GDB later then start QEMU without “-S” in the above example:
shell1$ fx qemu -- -s [... some QEMU start up text ...]
You will then need to locate zircon.elf
in the out
directory.
And then in the shell you're running GDB in:
shell2$ gdb path-to-zircon.elf -x ${FUCHSIA_DIR}/zircon/kernel/scripts/zircon.elf-gdb.py Reading symbols from /fuchsia/out/default/kernel_x64-clang/zircon.elf... Loading zircon.elf-gdb.py ... Zircon extensions installed for /fuchsia/out/default/kernel_x64-clang/zircon.elf (gdb) target extended-remote :1234 Remote debugging using :1234 0x000000000000fff0 in ?? () Thread 1 hit Breakpoint -1, 0x0000000000100050 in ?? () Watchpoint set on KASLR relocated base variable Thread 1 hit Hardware read watchpoint -2: *0x767ca0 Value = 0 0x00000000001000ef in ?? () Update symbols and breakpoints for KASLR KASLR: Correctly reloaded kernel at 0xffffffff00000000 (gdb) # Don't try to do too much at this point. (gdb) # GDB can't handle architecture switching in one session, (gdb) # and at this point the architecture is 16-bit x86. (gdb) break lk_main Breakpoint 1 at 0xfffffffff010cb58: file kernel/top/main.c, line 59. (gdb) continue Continuing. Breakpoint 1, lk_main (arg0=1, arg1=18446744071568293116, arg2=0, arg3=0) at kernel/top/main.c:59 59 { (gdb) continue
At this point Zircon boots and back in shell1 you'll be at the Zircon prompt.
mxsh>
If you Ctrl-C in shell2 at this point you can get back to GDB.
(gdb) # Having just done "continue" ^C Program received signal SIGINT, Interrupt. arch_idle () at kernel/arch/x86/64/ops.S:32 32 ret (gdb) info threads Id Target Id Frame 4 Thread 4 (CPU#3 [halted ]) arch_idle () at kernel/arch/x86/64/ops.S:32 3 Thread 3 (CPU#2 [halted ]) arch_idle () at kernel/arch/x86/64/ops.S:32 2 Thread 2 (CPU#1 [halted ]) arch_idle () at kernel/arch/x86/64/ops.S:32 * 1 Thread 1 (CPU#0 [halted ]) arch_idle () at kernel/arch/x86/64/ops.S:32
QEMU reports one thread to GDB for each CPU.
The zircon/kernel/scripts/zircon.elf-gdb.py
script should be automatically loaded by gdb. If it‘s not loaded automatically, you might need to add its path to gdb’s auto-load-safe-path. Alternatively, you can add manually set it in gdb's command line flag:
$ gdb path-to-zircon.elf -x ${FUCHSIA_DIR}/zircon/kernel/scripts/zircon.elf-gdb.py
It provides several things:
KASLR relocation for gdb, allowing you to correctly set breakpoints in functions.
Pretty-printers for zircon objects (alas none at the moment).
Several zircon specific commands, all with a “zircon” prefix. To see them:
(gdb) help info zircon (gdb) help set zircon (gdb) help show zircon
Heads up: This script isn't always updated as zircon changes.
NOTE: due to bug 67893, the KASLR part might not work if using qemu with kvm. As a workaround, you can execute the following in gdb:
(gdb) # before attaching to qemu (gdb) mem 0 0xffffffffffffffff ro (gdb) target extended-remote :1234 (gdb) ... (gdb) # after the script performed the kaslr relocations (gdb) mem auto
To terminate QEMU you can send commands to QEMU from GDB:
(gdb) monitor quit (gdb) quit
To see the list of QEMU commands you can execute from GDB:
(gdb) monitor help
If you have a crash that is difficult to debug, or that you need help with debugging, it's possible to save system state akin to a core dump.
bash$ qemu-img create -f qcow2 /tmp/my_snapshots.qcow2 32M
will create a “32M” block storage device. Next launch QEMU and tell it about the device, but don‘t tell it to attach the device to the guest system. This is OK; we don’t plan on using it to back up the disk state, we just want a core dump. Note: all of this can be skipped if you are already emulating a block device and it is using the qcow2 format.
bash$ qemu <normal_launch_args> -drive if=none,format=qcow2,file=/tmp/my_snapshots.qcow2
When you get to a point where you want to save the core state, drop to the QEMU console using . You should get the (qemu) prompt at this point. From here, just say:
(qemu) savevm my_backup_tag_name
Later on, from an identical machine (one launched with the same args as before), you can drop to the console and run:
(qemu) loadvm my_backup_tag_name
to restore the state. Alternatively, you can do it from the cmd line with:
bash$ qemu <normal_launch_args> -drive if=none,format=qcow2,file=/tmp/my_snapshots.qcow2 -loadvm my_backup_tag_name
In theory, you could package up the qcow2 image along with your build output directory and anyone should be able to restore your state and start to poke at stuff from the QEMU console.