gn的编译需要使用clang编译器，并且gn使用了C++17的语法，所以需要使用较高版本的clang。

编译 gn

zircon下载

https://hexang.org/mirrors/fuchsia/-/tree/7eb369f72ffa9f505f56a9168a3b4d6a3ac86de2/zircon

下载完成之后, 在 $ZIRCON 目录下多出来了一个 prebuilt 目录,
从目录中可以看出, 上面的命令下载了以下几个文件.

修改项目工程对clang，gcc的链接路径

Zircon Getting Started

Quick Start Recipes

Checking out the Zircon source code

Note: The Fuchsia source includes Zircon. See Fuchsia's Getting Started doc. Follow this doc to work on only Zircon.

The Zircon Git repository is located at: fuchsia.googlesource.com/zircon

To clone the repository, assuming you setup the $SRC variable in your environment:

git clone https://fuchsia.googlesource.com/zircon $SRC/zircon
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For the purpose of this document, we will assume that Zircon is checked out in $SRC/zircon and that we will build toolchains, QEMU, etc alongside that. Various ninja invocations are presented with a "-j32" option for parallelization. If that's excessive for the machine you're building on, try -j16 or -j8.

Preparing the build environment

Ubuntu

On Ubuntu this should obtain the necessary pre-reqs:

sudo apt-get install texinfo libglib2.0-dev autoconf libtool bison libsdl-dev build-essential
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macOS

Install the Xcode Command Line Tools:

xcode-select --install
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Install the other pre-reqs:

Using Homebrew:

brew install wget pkg-config glib autoconf automake libtool
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Using MacPorts:

port install autoconf automake libtool libpixman pkgconfig glib2
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Install Toolchains and Prebuilts

If you're developing on Linux or macOS, there are prebuilt toolchain binaries available. Just run this script from your Zircon working directory:

./scripts/download-prebuilt
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If you would like to build the toolchains yourself, follow the instructions later in the document.

Build Zircon

Build results will be in $SRC/zircon/build-zircon.

cd $SRC/zircon
gn gen build-zircon

# for both aarch64 and x64
ninja -C build-zircon

# for aarch64
ninja -C build-zircon arm64

# for x64
ninja -C build-zircon x64
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Using Clang

To build Zircon using Clang as the target toolchain, set the variants = [ "clang" ] build argument when invoking GN.

cd $SRC/zircon
gn gen build-zircon --args='variants = [ "clang" ]'

# for both aarch64 and x64
ninja -C build-zircon

# for aarch64
ninja -C build-zircon arm64

# for x64
ninja -C build-zircon x64
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Building Zircon for all targets

# The -r enables release builds as well
./scripts/buildall -r
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Please build for all targets before submitting to ensure builds work on all architectures.

QEMU

You can skip this if you're only testing on actual hardware, but the emulator is handy for quick local tests and generally worth having around.

See QEMU for information on building and using QEMU with zircon.

Build Toolchains (Optional)

If the prebuilt toolchain binaries do not work for you, you can build your own from vanilla upstream sources.

The GCC toolchain is used to build Zircon by default.
The Clang toolchain is used to build Zircon if you build with variants = [ "clang" ] or variants = [ "asan" ].
The Clang toolchain is also used by default to build host-side code, but any C++14-capable toolchain for your build host should work fine.

Build one or the other or both, as needed for how you want build Zircon.

GCC Toolchain

We use GNU binutils 2.30(*) and GCC 8.2(**), configured with --enable-initfini-array --enable-gold, and with --target=x86_64-elf --enable-targets=x86_64-pep for x86-64 or --target=aarch64-elf for ARM64.

For binutils, we recommend --enable-deterministic-archives but that switch is not necessary to get a working build.

For GCC, it's necessary to pass MAKEOVERRIDES=USE_GCC_STDINT=provide on the make command line. This should ensure that the stdint.h GCC installs is one that works standalone (stdint-gcc.h in the source) rather than one that uses #include_next and expects another stdint.h file installed elsewhere.

Only the C and C++ language support is required and no target libraries other than libgcc are required, so you can use various configure switches to disable other things and make your build of GCC itself go more quickly and use less storage, e.g. --enable-languages=c,c++ --disable-libstdcxx --disable-libssp --disable-libquadmath. See the GCC installation documentation for more details.

You may need various other configure switches or other prerequisites to build on your particular host system. See the GNU documentation.

(*) The binutils 2.30 release has some harmless make check failures in the aarch64-elf and x86_64-elf configurations. These are fixed on the upstream binutils-2_30-branch git branch, which is what we actually build. But the 2.30 release version works fine for building Zircon; it just has some spurious failures in its own test suite.

(**) As of 2008-6-15, GCC 8.2 has not been released yet. There is no released version of GCC that works for building Zircon without backporting some fixes. What we actually use is the upstream gcc-8-branch git branch.

Clang/LLVM Toolchain

We use a trunk snapshot of Clang and update to new snapshots frequently. Any build of recent-enough Clang with support for x86_64 and aarch64 compiled in should work. You'll need a toolchain that also includes the runtime libraries. We normally also use the same build of Clang for the host as well as for the *-fuchsia targets. See here for details on how we build Clang.

Set up build arguments for toolchains

If you're using the prebuilt toolchains, you can skip this step, since the build will find them automatically.

Set the build argument that points to where you installed the toolchains:

# in args.gn or passed to --args
clang_tool_dir = "<absolute path to>/clang-install/bin/"
gcc_tool_dir = "<absolute path to>/gcc-install/bin/"
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Note that *_tool_dir should have a trailing slash. If the clang or gcc in your PATH works for Zircon, you can just use empty prefixes.

Copying files to and from Zircon

With local link IPv6 configured, the host tool ./build-ARCH/tools/netcp can be used to copy files.

# Copy the file myprogram to Zircon
netcp myprogram :/tmp/myprogram

# Copy the file myprogram back to the host
netcp :/tmp/myprogram myprogram
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Including Additional Userspace Files

The Zircon build creates a bootfs image containing necessary userspace components for the system to boot (the device manager, some device drivers, etc). The kernel is capable of including a second bootfs image which is provided by QEMU or the bootloader as a ramdisk image.

To create such a bootfs image, use the zbi tool that's generated as part of the build. It can assemble a bootfs image for either source directories (in which case every file in the specified directory and its subdirectories are included) or via a manifest file which specifies on a file-by-file basis which files to include.

$BUILDDIR/tools/zbi -o extra.bootfs @/path/to/directory

echo "issue.txt=/etc/issue" > manifest
echo "etc/hosts=/etc/hosts" >> manifest
$BUILDDIR/tools/zbi -o extra.bootfs manifest
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On the booted Zircon system, the files in the bootfs will appear under /boot, so in the above manifest example, the "hosts" file would appear at /boot/etc/hosts.

Network Booting

Network booting is supported via two mechanisms: Gigaboot and Zirconboot. Gigaboot is an EFI based bootloader whereas zirconboot is a mechanism that allows a minimal zircon system to serve as a bootloader for zircon.

On systems that boot via EFI (such as Acer and NUC), either option is viable. On other systems, zirconboot may be the only option for network booting.

Via Gigaboot

The GigaBoot20x6 bootloader speaks a simple network boot protocol (over IPV6 UDP) which does not require any special host configuration or privileged access to use.

It does this by taking advantage of IPV6 Link Local Addressing and Multicast, allowing the device being booted to advertise its bootability and the host to find it and send a system image to it.

If you have a device (for example a Broadwell or Skylake Intel NUC) running GigaBoot20x6, first create a USB drive.

$BUILDDIR/tools/bootserver $BUILDDIR/zircon.bin

# if you have an extra bootfs image (see above):
$BUILDDIR/tools/bootserver $BUILDDIR/zircon.bin /path/to/extra.bootfs
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By default bootserver will continue to run and every time it observes a netboot beacon it will send the kernel (and bootfs if provided) to that device. If you pass the -1 option, bootserver will exit after a successful boot instead.

Via Zirconboot

Zirconboot is a mechanism that allows a zircon system to serve as the bootloader for zircon itself. Zirconboot speaks the same boot protocol as Gigaboot described above.

To use zirconboot, pass the netsvc.netboot=true argument to zircon via the kernel command line. When zirconboot starts, it will attempt to fetch and boot into a zircon system from a bootserver running on the attached host.

Network Log Viewing

The default build of Zircon includes a network log service that multicasts the system log over the link local IPv6 UDP. Please note that this is a quick hack and the protocol will certainly change at some point.

For now, if you're running Zircon on QEMU with the -N flag or running on hardware with a supported ethernet interface (ASIX USB Dongle or Intel Ethernet on NUC), the loglistener tool will observe logs broadcast over the local link:

$BUILDDIR/tools/loglistener
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Debugging

For random tips on debugging in the zircon environment see debugging.

Contribute changes

See contributing.md.