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Merge pull request #8315 from fricklerhandwerk/doc-system
add information on the system type string
This commit is contained in:
Robert Hensing
GitHub
commit
eca07b2a47
3 changed files with 89 additions and 43 deletions
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@ -5,7 +5,14 @@ AC_CONFIG_AUX_DIR(config)
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AC_PROG_SED
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# Construct a Nix system name (like "i686-linux").
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# Construct a Nix system name (like "i686-linux"):
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# https://www.gnu.org/software/autoconf/manual/html_node/Canonicalizing.html#index-AC_005fCANONICAL_005fHOST-1
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# The inital value is produced by the `config/config.guess` script:
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# upstream: https://git.savannah.gnu.org/cgit/config.git/tree/config.guess
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# It has the following form, which is not documented anywhere:
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# <cpu>-<vendor>-<os>[<version>][-<abi>]
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# If `./configure` is passed any of the `--host`, `--build`, `--target` options, the value comes from `config/config.sub` instead:
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# upstream: https://git.savannah.gnu.org/cgit/config.git/tree/config.sub
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AC_CANONICAL_HOST
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AC_MSG_CHECKING([for the canonical Nix system name])
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@ -110,41 +110,72 @@ You can also build Nix for one of the [supported platforms](#platforms).
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## Platforms
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As specified in [`flake.nix`], Nix can be built for various platforms:
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- `aarch64-linux`
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- `i686-linux`
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- `x86_64-darwin`
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- `x86_64-linux`
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Nix can be built for various platforms, as specified in [`flake.nix`]:
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[`flake.nix`]: https://github.com/nixos/nix/blob/master/flake.nix
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- `x86_64-linux`
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- `x86_64-darwin`
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- `i686-linux`
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- `aarch64-linux`
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- `aarch64-darwin`
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- `armv6l-linux`
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- `armv7l-linux`
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In order to build Nix for a different platform than the one you're currently
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on, you need to have some way for your system Nix to build code for that
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platform. Common solutions include [remote builders] and [binfmt emulation]
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on, you need a way for your current Nix installation to build code for that
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platform. Common solutions include [remote builders] and [binary format emulation]
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(only supported on NixOS).
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[remote builders]: ../advanced-topics/distributed-builds.md
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[binfmt emulation]: https://nixos.org/manual/nixos/stable/options.html#opt-boot.binfmt.emulatedSystems
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These solutions let Nix perform builds as if you're on the native platform, so
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executing the build is as simple as
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```console
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$ nix build .#packages.aarch64-linux.default
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```
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for flake-enabled Nix, or
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Given such a setup, executing the build only requires selecting the respective attribute.
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For example, to compile for `aarch64-linux`:
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```console
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$ nix-build --attr packages.aarch64-linux.default
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```
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for classic Nix.
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or for Nix with the [`flakes`] and [`nix-command`] experimental features enabled:
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You can use any of the other supported platforms in place of `aarch64-linux`.
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```console
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$ nix build .#packages.aarch64-linux.default
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```
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Cross-compiled builds are available for ARMv6 and ARMv7, and Nix on unsupported platforms can be bootstrapped by adding more `crossSystems` in `flake.nix`.
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Cross-compiled builds are available for ARMv6 (`armv6l-linux`) and ARMv7 (`armv7l-linux`).
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Add more [system types](#system-type) to `crossSystems` in `flake.nix` to bootstrap Nix on unsupported platforms.
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## System type
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Nix uses a string with he following format to identify the *system type* or *platform* it runs on:
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```
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<cpu>-<os>[-<abi>]
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```
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It is set when Nix is compiled for the given system, and based on the output of [`config.guess`](https://github.com/nixos/nix/blob/master/config/config.guess) ([upstream](https://git.savannah.gnu.org/cgit/config.git/tree/config.guess)):
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```
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<cpu>-<vendor>-<os>[<version>][-<abi>]
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```
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When Nix is built such that `./configure` is passed any of the `--host`, `--build`, `--target` options, the value is based on the output of [`config.sub`](https://github.com/nixos/nix/blob/master/config/config.sub) ([upstream](https://git.savannah.gnu.org/cgit/config.git/tree/config.sub)):
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```
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<cpu>-<vendor>[-<kernel>]-<os>
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```
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For historic reasons and backward-compatibility, some CPU and OS identifiers are translated from the GNU Autotools naming convention in [`configure.ac`](https://github.com/nixos/nix/blob/master/config/config.sub) as follows:
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| `config.guess` | Nix |
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|----------------------------|---------------------|
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| `amd64` | `x86_64` |
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| `i*86` | `i686` |
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| `arm6` | `arm6l` |
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| `arm7` | `arm7l` |
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| `linux-gnu*` | `linux` |
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| `linux-musl*` | `linux` |
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## Compilation environments
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@ -193,18 +193,24 @@ public:
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Setting<std::string> thisSystem{
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this, SYSTEM, "system",
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R"(
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This option specifies the canonical Nix system name of the current
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installation, such as `i686-linux` or `x86_64-darwin`. Nix can only
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build derivations whose `system` attribute equals the value
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specified here. In general, it never makes sense to modify this
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value from its default, since you can use it to ‘lie’ about the
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platform you are building on (e.g., perform a Mac OS build on a
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Linux machine; the result would obviously be wrong). It only makes
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sense if the Nix binaries can run on multiple platforms, e.g.,
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‘universal binaries’ that run on `x86_64-linux` and `i686-linux`.
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The system type of the current Nix installation.
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Nix will only build a given [derivation](@docroot@/language/derivations.md) locally when its `system` attribute equals any of the values specified here or in [`extra-platforms`](#conf-extra-platforms).
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It defaults to the canonical Nix system name detected by `configure`
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at build time.
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The default value is set when Nix itself is compiled for the system it will run on.
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The following system types are widely used, as [Nix is actively supported on these platforms](@docroot@/contributing/hacking.md#platforms):
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- `x86_64-linux`
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- `x86_64-darwin`
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- `i686-linux`
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- `aarch64-linux`
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- `aarch64-darwin`
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- `armv6l-linux`
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- `armv7l-linux`
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In general, you do not have to modify this setting.
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While you can force Nix to run a Darwin-specific `builder` executable on a Linux machine, the result would obviously be wrong.
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This value is available in the Nix language as [`builtins.currentSystem`](@docroot@/language/builtin-constants.md#builtins-currentSystem).
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)"};
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Setting<time_t> maxSilentTime{
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@ -670,18 +676,20 @@ public:
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getDefaultExtraPlatforms(),
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"extra-platforms",
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R"(
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Platforms other than the native one which this machine is capable of
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building for. This can be useful for supporting additional
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architectures on compatible machines: i686-linux can be built on
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x86\_64-linux machines (and the default for this setting reflects
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this); armv7 is backwards-compatible with armv6 and armv5tel; some
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aarch64 machines can also natively run 32-bit ARM code; and
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qemu-user may be used to support non-native platforms (though this
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may be slow and buggy). Most values for this are not enabled by
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default because build systems will often misdetect the target
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platform and generate incompatible code, so you may wish to
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cross-check the results of using this option against proper
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natively-built versions of your derivations.
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System types of executables that can be run on this machine.
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Nix will only build a given [derivation](@docroot@/language/derivations.md) locally when its `system` attribute equals any of the values specified here or in the [`system` option](#conf-system).
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Setting this can be useful to build derivations locally on compatible machines:
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- `i686-linux` executables can be run on `x86_64-linux` machines (set by default)
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- `x86_64-darwin` executables can be run on macOS `aarch64-darwin` with Rosetta 2 (set by default where applicable)
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- `armv6` and `armv5tel` executables can be run on `armv7`
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- some `aarch64` machines can also natively run 32-bit ARM code
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- `qemu-user` may be used to support non-native platforms (though this
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may be slow and buggy)
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Build systems will usually detect the target platform to be the current physical system and therefore produce machine code incompatible with what may be intended in the derivation.
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You should design your derivation's `builder` accordingly and cross-check the results when using this option against natively-built versions of your derivation.
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)", {}, false};
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Setting<StringSet> systemFeatures{
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