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Move builder execution to store layer

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It is not a language topic.
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John Ericson 2025-01-19 15:16:42 -05:00
parent 87c559e4aa
commit 96a46f9995
3 changed files with 75 additions and 76 deletions
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3
doc/manual/redirects.js
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@ -346,6 +346,9 @@ const redirects = {
"scoping-rules": "scoping.html",
"string-literal": "string-literals.html",
},
"language/derivations.md": {
"builder-execution": "store/drv/building.md#building"
},
"installation/installing-binary.html": {
"linux": "uninstall.html#linux",
"macos": "uninstall.html#macos",

74
doc/manual/source/language/derivations.md
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@ -235,77 +235,3 @@ It outputs an attribute set, and produces a [derivation] as a side effect of eva
passed as an empty string.
<!-- FIXME: add a section on output attributes -->
## Builder execution
The [`builder`](#attr-builder) is executed as follows:
- A temporary directory is created under the directory specified by
`TMPDIR` (default `/tmp`) where the build will take place. The
current directory is changed to this directory.
- The environment is cleared and set to the derivation attributes, as
specified above.
- In addition, the following variables are set:
- `NIX_BUILD_TOP` contains the path of the temporary directory for
this build.
- Also, `TMPDIR`, `TEMPDIR`, `TMP`, `TEMP` are set to point to the
temporary directory. This is to prevent the builder from
accidentally writing temporary files anywhere else. Doing so
might cause interference by other processes.
- `PATH` is set to `/path-not-set` to prevent shells from
initialising it to their built-in default value.
- `HOME` is set to `/homeless-shelter` to prevent programs from
using `/etc/passwd` or the like to find the user's home
directory, which could cause impurity. Usually, when `HOME` is
set, it is used as the location of the home directory, even if
it points to a non-existent path.
- `NIX_STORE` is set to the path of the top-level Nix store
directory (typically, `/nix/store`).
- `NIX_ATTRS_JSON_FILE` & `NIX_ATTRS_SH_FILE` if `__structuredAttrs`
is set to `true` for the derivation. A detailed explanation of this
behavior can be found in the
[section about structured attrs](./advanced-attributes.md#adv-attr-structuredAttrs).
- For each output declared in `outputs`, the corresponding
environment variable is set to point to the intended path in the
Nix store for that output. Each output path is a concatenation
of the cryptographic hash of all build inputs, the `name`
attribute and the output name. (The output name is omitted if
it’s `out`.)
- If an output path already exists, it is removed. Also, locks are
acquired to prevent multiple Nix instances from performing the same
build at the same time.
- A log of the combined standard output and error is written to
`/nix/var/log/nix`.
- The builder is executed with the arguments specified by the
attribute `args`. If it exits with exit code 0, it is considered to
have succeeded.
- The temporary directory is removed (unless the `-K` option was
specified).
- If the build was successful, Nix scans each output path for
references to input paths by looking for the hash parts of the input
paths. Since these are potential runtime dependencies, Nix registers
them as dependencies of the output paths.
- After the build, Nix sets the last-modified timestamp on all files
in the build result to 1 (00:00:01 1/1/1970 UTC), sets the group to
the default group, and sets the mode of the file to 0444 or 0555
(i.e., read-only, with execute permission enabled if the file was
originally executable). Note that possible `setuid` and `setgid`
bits are cleared. Setuid and setgid programs are not currently
supported by Nix. This is because the Nix archives used in
deployment have no concept of ownership information, and because it
makes the build result dependent on the user performing the build.

74
doc/manual/source/store/drv/building.md
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@ -9,9 +9,79 @@ TODO
Each input must be [realised] prior to building the derivation in question.
At that point, the derivation can be *normalized*, by replacing each input deriving path with its store path --- which we now know since we've realised it.
## Building
## Builder Execution
TODO
The [`builder`](../drv.md#builder) is executed as follows:
- A temporary directory is created under the directory specified by
`TMPDIR` (default `/tmp`) where the build will take place. The
current directory is changed to this directory.
- The environment is cleared and set to the derivation attributes, as
specified above.
- In addition, the following variables are set:
- `NIX_BUILD_TOP` contains the path of the temporary directory for
this build.
- Also, `TMPDIR`, `TEMPDIR`, `TMP`, `TEMP` are set to point to the
temporary directory. This is to prevent the builder from
accidentally writing temporary files anywhere else. Doing so
might cause interference by other processes.
- `PATH` is set to `/path-not-set` to prevent shells from
initialising it to their built-in default value.
- `HOME` is set to `/homeless-shelter` to prevent programs from
using `/etc/passwd` or the like to find the user's home
directory, which could cause impurity. Usually, when `HOME` is
set, it is used as the location of the home directory, even if
it points to a non-existent path.
- `NIX_STORE` is set to the path of the top-level Nix store
directory (typically, `/nix/store`).
- `NIX_ATTRS_JSON_FILE` & `NIX_ATTRS_SH_FILE` if `__structuredAttrs`
is set to `true` for the derivation. A detailed explanation of this
behavior can be found in the
[section about structured attrs](@docroot@/language/advanced-attributes.md#adv-attr-structuredAttrs).
- For each output declared in `outputs`, the corresponding
environment variable is set to point to the intended path in the
Nix store for that output. Each output path is a concatenation
of the cryptographic hash of all build inputs, the `name`
attribute and the output name. (The output name is omitted if
it’s `out`.)
- If an output path already exists, it is removed. Also, locks are
acquired to prevent multiple Nix instances from performing the same
build at the same time.
- A log of the combined standard output and error is written to
`/nix/var/log/nix`.
- The builder is executed with the arguments specified by the
attribute `args`. If it exits with exit code 0, it is considered to
have succeeded.
- The temporary directory is removed (unless the `-K` option was
specified).
- If the build was successful, Nix scans each output path for
references to input paths by looking for the hash parts of the input
paths. Since these are potential runtime dependencies, Nix registers
them as dependencies of the output paths.
- After the build, Nix sets the last-modified timestamp on all files
in the build result to 1 (00:00:01 1/1/1970 UTC), sets the group to
the default group, and sets the mode of the file to 0444 or 0555
(i.e., read-only, with execute permission enabled if the file was
originally executable). Note that possible `setuid` and `setgid`
bits are cleared. Setuid and setgid programs are not currently
supported by Nix. This is because the Nix archives used in
deployment have no concept of ownership information, and because it
makes the build result dependent on the user performing the build.
## Processing outputs and Reference scanning