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+# `cf-protection`
+
+This option enables control-flow enforcement technology (CET) on x86; a more detailed description of
+CET is available [here]. Similar to `clang`, this flag takes one of the following values:
+
+- `none` - Disable CET completely (this is the default).
+- `branch` - Enable indirect branch tracking (`IBT`).
+- `return` - Enable shadow stack (`SHSTK`).
+- `full` - Enable both `branch` and `return`.
+
+[here]: https://www.intel.com/content/www/us/en/develop/articles/technical-look-control-flow-enforcement-technology.html
+
+This flag only applies to the LLVM backend: it sets the `cf-protection-branch` and
+`cf-protection-return` flags on LLVM modules. Note, however, that all compiled modules linked
+together must have the flags set for the compiled output to be CET-enabled. Currently, Rust's
+standard library does not ship with CET enabled by default, so you may need to rebuild all standard
+modules with a `cargo` command like:
+
+```sh
+$ RUSTFLAGS="-Z cf-protection=full" RUSTC="rustc-custom" cargo +nightly build -Z build-std --target x86_64-unknown-linux-gnu
+```
+
+### Detection
+
+An ELF binary is CET-enabled if it has the `IBT` and `SHSTK` tags, e.g.:
+
+```sh
+$ readelf -a target/x86_64-unknown-linux-gnu/debug/example | grep feature:
+      Properties: x86 feature: IBT, SHSTK
+```
+
+### Troubleshooting
+
+To display modules that are not CET enabled, examine the linker errors available when `cet-report` is enabled:
+
+```sh
+$ RUSTC_LOG=rustc_codegen_ssa::back::link=info rustc-custom -v -Z cf-protection=full -C link-arg="-Wl,-z,cet-report=warning" -o example example.rs
+...
+/usr/bin/ld: /.../build/x86_64-unknown-linux-gnu/stage1/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-d73f7266be14cb8b.rlib(std-d73f7266be14cb8b.std.f7443020-cgu.12.rcgu.o): warning: missing IBT and SHSTK properties
+```