Module rustc_target::spec
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Flexible target specification.
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.
Using custom targets
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.
Projects defining their own targets should use
--target=path/to/my-awesome-platform.json instead of adding to
RUST_TARGET_PATH.
Defining a new target
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
llvm-target, target-endian, target-pointer-width, data-layout,
arch, and os. In general, options passed to rustc with -C override
the target’s settings, though target-feature and link-args will add
to the list specified by the target, rather than replace.
Modules
a32 code by default.t32 code by default.wasm32-wasi target is a new and still (as of April 2019) an
experimental target. The definition in this file is likely to be tweaked
over time and shouldn’t be relied on too much.Macros
Structs
rustc knows about how to compile for a specific target.json.