Rust targets a wide variety of usecases, and in the interest of flexibility, allows new target triples to be defined in configuration files. Most users will not need to care about these, but this is invaluable when porting Rust to a new platform, and allows for an unprecedented level of control over how the compiler works.
A target triple, as passed via
rustc --target=TRIPLE, will first be
compared against the list of built-in targets. This is to ease distributing
rustc (no need for configuration files) and also to hold these built-in
targets as immutable and sacred. If
TRIPLE is not one of the built-in
targets, rustc will check if a file named
TRIPLE exists. If it does, it
will be loaded as the target configuration. If the file does not exist,
rustc will search each directory in the environment variable
RUST_TARGET_PATH for a file named
TRIPLE.json. The first one found will
be loaded. If no file is found in any of those directories, a fatal error
will be given.
/etc/rustc as its last entry,
to be searched by default.
Projects defining their own targets should use
--target=path/to/my-awesome-platform.json instead of adding to
Targets are defined using JSON. The
Target struct in
this module defines the format the JSON file should take, though each
underscore in the field names should be replaced with a hyphen (
-) in the
JSON file. Some fields are required in every target specification, such as
arch. In general, options passed to rustc with
-C override the target's
link-args will add to the list
specified by the target, rather than replace.
Optional aspects of a target specification.