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move docs of the current system to the system setting

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add information what happens when Nix itself is cross-compiled
This commit is contained in:
Valentin Gagarin 2023-05-31 03:48:05 +02:00
parent 0751c1bfc6
commit c8a42039ea
2 changed files with 43 additions and 4 deletions
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2
configure.ac
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@ -11,6 +11,8 @@ AC_PROG_SED
# 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.sub` instead:
# https://git.savannah.gnu.org/cgit/config.git/tree/config.sub
AC_CANONICAL_HOST
AC_MSG_CHECKING([for the canonical Nix system name])

45
src/libstore/globals.hh
View file

@ -193,12 +193,49 @@ 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).
The system type of the current Nix installation.
Nix can only build [derivations](@docroot@/language/derivations.md) whose `system` attribute equals the value specified here.
In general, it never makes sense to modify this value, since you can use it to ‘lie’ about the system you are building on (e.g., perform a macOS 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 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:
- `x86_64-linux`
- `x86_64-darwin`
- `i686-linux`
- `aarch64-linux`
- `aarch64-darwin`
The concrete value is based on the output of [`config.guess`](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://git.savannah.gnu.org/cgit/config.git/tree/config.sub):
```
<cpu>-<vendor>[-<kernel>]-<os>
```
Nix only uses the CPU and OS identifiers:
```
<cpu>-<os>[-<abi>]
```
For historic reasons and backwards-compatibility, some CPU and OS identifiers are transformed as follows:
| `config.guess` | Nix |
|----------------------------|---------------------|
| `amd64` | `x86_64` |
| `i*86` | `i686` |
| `arm6` | `arm6l` |
| `arm7` | `arm7l` |
| `linux-gnu*` | `linux` |
| `linux-musl*` | `linux` |
)"};
Setting<time_t> maxSilentTime{