diff options
| -rw-r--r-- | configure.ac | 9 | ||||
| -rw-r--r-- | doc/manual/src/contributing/hacking.md | 63 | ||||
| -rw-r--r-- | src/libstore/globals.hh | 56 |
3 files changed, 87 insertions, 41 deletions
diff --git a/configure.ac b/configure.ac index bb3f92e4d..6d78237f0 100644 --- a/configure.ac +++ b/configure.ac @@ -5,7 +5,14 @@ AC_CONFIG_AUX_DIR(config) AC_PROG_SED -# Construct a Nix system name (like "i686-linux"). +# Construct a Nix system name (like "i686-linux"): +# https://www.gnu.org/software/autoconf/manual/html_node/Canonicalizing.html#index-AC_005fCANONICAL_005fHOST-1 +# The inital value is produced by the `config/config.guess` script: +# upstream: https://git.savannah.gnu.org/cgit/config.git/tree/config.guess +# It has the following form, which is not documented anywhere: +# <cpu>-<vendor>-<os>[<version>][-<abi>] +# If `./configure` is passed any of the `--host`, `--build`, `--target` options, the value comes from `config/config.sub` instead: +# upstream: https://git.savannah.gnu.org/cgit/config.git/tree/config.sub AC_CANONICAL_HOST AC_MSG_CHECKING([for the canonical Nix system name]) diff --git a/doc/manual/src/contributing/hacking.md b/doc/manual/src/contributing/hacking.md index 7b2440971..b8ea977d7 100644 --- a/doc/manual/src/contributing/hacking.md +++ b/doc/manual/src/contributing/hacking.md @@ -110,41 +110,72 @@ You can also build Nix for one of the [supported platforms](#platforms). ## Platforms -As specified in [`flake.nix`], Nix can be built for various platforms: - -- `aarch64-linux` -- `i686-linux` -- `x86_64-darwin` -- `x86_64-linux` +Nix can be built for various platforms, as specified in [`flake.nix`]: [`flake.nix`]: https://github.com/nixos/nix/blob/master/flake.nix +- `x86_64-linux` +- `x86_64-darwin` +- `i686-linux` +- `aarch64-linux` +- `aarch64-darwin` +- `armv6l-linux` +- `armv7l-linux` + In order to build Nix for a different platform than the one you're currently -on, you need to have some way for your system Nix to build code for that -platform. Common solutions include [remote builders] and [binfmt emulation] +on, you need a way for your current Nix installation to build code for that +platform. Common solutions include [remote builders] and [binary format emulation] (only supported on NixOS). [remote builders]: ../advanced-topics/distributed-builds.md [binfmt emulation]: https://nixos.org/manual/nixos/stable/options.html#opt-boot.binfmt.emulatedSystems -These solutions let Nix perform builds as if you're on the native platform, so -executing the build is as simple as +Given such a setup, executing the build only requires selecting the respective attribute. +For example, to compile for `aarch64-linux`: ```console -$ nix build .#packages.aarch64-linux.default +$ nix-build --attr packages.aarch64-linux.default ``` -for flake-enabled Nix, or +or for Nix with the [`flakes`] and [`nix-command`] experimental features enabled: ```console -$ nix-build --attr packages.aarch64-linux.default +$ nix build .#packages.aarch64-linux.default ``` -for classic Nix. +Cross-compiled builds are available for ARMv6 (`armv6l-linux`) and ARMv7 (`armv7l-linux`). +Add more [system types](#system-type) to `crossSystems` in `flake.nix` to bootstrap Nix on unsupported platforms. + +## System type + +Nix uses a string with he following format to identify the *system type* or *platform* it runs on: + +``` +<cpu>-<os>[-<abi>] +``` + +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)): + +``` +<cpu>-<vendor>-<os>[<version>][-<abi>] +``` + +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)): + +``` +<cpu>-<vendor>[-<kernel>]-<os> +``` -You can use any of the other supported platforms in place of `aarch64-linux`. +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: -Cross-compiled builds are available for ARMv6 and ARMv7, and Nix on unsupported platforms can be bootstrapped by adding more `crossSystems` in `flake.nix`. +| `config.guess` | Nix | +|----------------------------|---------------------| +| `amd64` | `x86_64` | +| `i*86` | `i686` | +| `arm6` | `arm6l` | +| `arm7` | `arm7l` | +| `linux-gnu*` | `linux` | +| `linux-musl*` | `linux` | ## Compilation environments diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh index d4b8fb1f9..723d18d74 100644 --- a/src/libstore/globals.hh +++ b/src/libstore/globals.hh @@ -193,18 +193,24 @@ public: Setting<std::string> thisSystem{ this, SYSTEM, "system", R"( - This option specifies the canonical Nix system name of the current - installation, such as `i686-linux` or `x86_64-darwin`. Nix can only - build derivations whose `system` attribute equals the value - specified here. In general, it never makes sense to modify this - value from its default, since you can use it to ‘lie’ about the - platform you are building on (e.g., perform a Mac OS build on a - Linux machine; the result would obviously be wrong). It only makes - sense if the Nix binaries can run on multiple platforms, e.g., - ‘universal binaries’ that run on `x86_64-linux` and `i686-linux`. - - It defaults to the canonical Nix system name detected by `configure` - at build time. + The system type of the current Nix installation. + 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). + + The default value is set when Nix itself is compiled for the system it will run on. + The following system types are widely used, as [Nix is actively supported on these platforms](@docroot@/contributing/hacking.md#platforms): + + - `x86_64-linux` + - `x86_64-darwin` + - `i686-linux` + - `aarch64-linux` + - `aarch64-darwin` + - `armv6l-linux` + - `armv7l-linux` + + In general, you do not have to modify this setting. + While you can force Nix to run a Darwin-specific `builder` executable on a Linux machine, the result would obviously be wrong. + + This value is available in the Nix language as [`builtins.currentSystem`](@docroot@/language/builtin-constants.md#builtins-currentSystem). )"}; Setting<time_t> maxSilentTime{ @@ -670,18 +676,20 @@ public: getDefaultExtraPlatforms(), "extra-platforms", R"( - Platforms other than the native one which this machine is capable of - building for. This can be useful for supporting additional - architectures on compatible machines: i686-linux can be built on - x86\_64-linux machines (and the default for this setting reflects - this); armv7 is backwards-compatible with armv6 and armv5tel; some - aarch64 machines can also natively run 32-bit ARM code; and - qemu-user may be used to support non-native platforms (though this - may be slow and buggy). Most values for this are not enabled by - default because build systems will often misdetect the target - platform and generate incompatible code, so you may wish to - cross-check the results of using this option against proper - natively-built versions of your derivations. + System types of executables that can be run on this machine. + + 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). + + Setting this can be useful to build derivations locally on compatible machines: + - `i686-linux` executables can be run on `x86_64-linux` machines (set by default) + - `x86_64-darwin` executables can be run on macOS `aarch64-darwin` with Rosetta 2 (set by default where applicable) + - `armv6` and `armv5tel` executables can be run on `armv7` + - some `aarch64` machines can also natively run 32-bit ARM code + - `qemu-user` may be used to support non-native platforms (though this + may be slow and buggy) + + 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. + You should design your derivation's `builder` accordingly and cross-check the results when using this option against natively-built versions of your derivation. )", {}, false}; Setting<StringSet> systemFeatures{ |