From: Yuki Okushi <huyuumi.dev@gmail.com>
Date: Wed, 14 Oct 2020 22:32:36 +0000 (+0900)
Subject: Rollup merge of #77934 - XAMPPRocky:codegen-backend-docs, r=jonas-schievink
X-Git-Url: https://git.lizzy.rs/?a=commitdiff_plain;h=0cf86c2e8a5d5ac653ded607611b424bbd3f571e;hp=b3f95124900a2d94e7f1eb5f8302d9c9d0858be2;p=rust.git

Rollup merge of #77934 - XAMPPRocky:codegen-backend-docs, r=jonas-schievink

Document -Z codegen-backend in the unstable book

### [Rendered](https://github.com/XAMPPRocky/rust/blob/codegen-backend-docs/src/doc/unstable-book/src/compiler-flags/codegen-backend.md)

Companion PR to #77933 tracking issue.

cc @bjorn3
---

diff --git a/src/doc/unstable-book/src/compiler-flags/codegen-backend.md b/src/doc/unstable-book/src/compiler-flags/codegen-backend.md
new file mode 100644
index 00000000000..878c894a6ca
--- /dev/null
+++ b/src/doc/unstable-book/src/compiler-flags/codegen-backend.md
@@ -0,0 +1,31 @@
+# `codegen-backend`
+
+The tracking issue for this feature is: [#77933](https://github.com/rust-lang/rust/issues/77933).
+
+------------------------
+
+This feature allows you to specify a path to a dynamic library to use as rustc's
+code generation backend at runtime.
+
+Set the `-Zcodegen-backend=<path>` compiler flag to specify the location of the
+backend. The library must be of crate type `dylib` and must contain a function
+named `__rustc_codegen_backend` with a signature of `fn() -> Box<dyn rustc_codegen_ssa::traits::CodegenBackend>`.
+
+## Example
+See also the [`hotplug_codegen_backend`](https://github.com/rust-lang/rust/tree/master/src/test/run-make-fulldeps/hotplug_codegen_backend) test
+for a full example.
+
+```rust,ignore
+use rustc_codegen_ssa::traits::CodegenBackend;
+
+struct MyBackend;
+
+impl CodegenBackend for MyBackend {
+   // Implement codegen methods
+}
+
+#[no_mangle]
+pub fn __rustc_codegen_backend() -> Box<dyn CodegenBackend> {
+    Box::new(MyBackend)
+}
+```