Rollup merge of #134760 - jieyouxu:enable-branch-protection-check-IBT, r=lqd

Migrate `branch-protection-check-IBT` to rmake.rs

- The Makefile version *never* ran because of Makefile syntax confusion because `ifeq ($(filter x86,$(LLVM_COMPONENTS)),x86_64)` [compares `x86` to `x86_64`, which always evaluates to false](https://github.com/rust-lang/rust/pull/126720#discussion_r1646808973).
- The test would've always failed because precompiled std is not built with `-Z cf-protection=branch`, but linkers require all input object files to indicate IBT support in order to enable IBT for the executable, which is not the case for std.
- Thus, the test input file is instead changed to a `no_std` program.
- The test is currently limited to only `x86_64-unknown-linux-gnu` host, there are various other problems when the test is cross-compiled that I didn't want to fix atm, and is left as an exercise for the `-Z cf-protection` implementers.

The GNU property note was added by #110304 in order to address #103001.

Partially supersedes #129156.
The rmake.rs port was initially authored by `@Rejyr` in #126720.
This PR is co-authored with `@Oneirical` and `@Rejyr.`

r? `@bjorn3` or reroll

try-job: x86_64-mingw-1
try-job: x86_64-mingw-2
try-job: x86_64-msvc
try-job: x86_64-apple-1
try-job: x86_64-apple-2

5 files changed, 58 insertions, 54 deletions

diff --git a/src/tools/tidy/src/allowed_run_make_makefiles.txt b/src/tools/tidy/src/allowed_run_make_makefiles.txt
index f7ecb485152..2f898187022 100644
--- a/src/tools/tidy/src/allowed_run_make_makefiles.txt
+++ b/src/tools/tidy/src/allowed_run_make_makefiles.txt
@@ -1,4 +1,3 @@
-run-make/branch-protection-check-IBT/Makefile
 run-make/cat-and-grep-sanity-check/Makefile
 run-make/extern-fn-reachable/Makefile
 run-make/jobserver-error/Makefile
diff --git a/tests/run-make/branch-protection-check-IBT/Makefile b/tests/run-make/branch-protection-check-IBT/Makefile
deleted file mode 100644
index ee0e034627f..00000000000
--- a/tests/run-make/branch-protection-check-IBT/Makefile
+++ /dev/null
@@ -1,21 +0,0 @@
-# Check for GNU Property Note
-
-include ../tools.mk
-
-# How to run this
-# python3 x.py test --target x86_64-unknown-linux-gnu  tests/run-make/branch-protection-check-IBT/
-
-# only-x86_64
-
-# ignore-test
-# FIXME(jieyouxu): This test never runs because the `ifeq` check on line 17
-# compares `x86` to `x86_64`, which always evaluates to false.
-# When the test does run, the compilation does not include `.note.gnu.property`.
-# See https://github.com/rust-lang/rust/pull/126720 for more information.
-
-all:
-ifeq ($(filter x86,$(LLVM_COMPONENTS)),x86_64)
-	$(RUSTC) --target x86_64-unknown-linux-gnu -Z cf-protection=branch -L$(TMPDIR) -C link-args='-nostartfiles'  -C save-temps  ./main.rs -o $(TMPDIR)/rsmain
-	 readelf -nW $(TMPDIR)/rsmain | $(CGREP) -e ".note.gnu.property"
-endif
-
diff --git a/tests/run-make/branch-protection-check-IBT/_rmake.rs b/tests/run-make/branch-protection-check-IBT/_rmake.rs
deleted file mode 100644
index 91151408785..00000000000
--- a/tests/run-make/branch-protection-check-IBT/_rmake.rs
+++ /dev/null
@@ -1,29 +0,0 @@
-// Check for GNU Property Note
-
-// How to run this
-// python3 x.py test --target x86_64-unknown-linux-gnu  tests/run-make/branch-protection-check-IBT/
-
-//@ only-x86_64
-
-//@ ignore-test
-// FIXME(jieyouxu): see the FIXME in the Makefile
-
-use run_make_support::{cwd, env_var, llvm_readobj, rustc};
-
-fn main() {
-    let llvm_components = env_var("LLVM_COMPONENTS");
-    if !format!(" {llvm_components} ").contains(" x86 ") {
-        return;
-    }
-
-    rustc()
-        .input("main.rs")
-        .target("x86_64-unknown-linux-gnu")
-        .arg("-Zcf-protection=branch")
-        .arg(format!("-L{}", cwd().display()))
-        .arg("-Clink-args=-nostartfiles")
-        .arg("-Csave-temps")
-        .run();
-
-    llvm_readobj().arg("-nW").input("main").run().assert_stdout_contains(".note.gnu.property");
-}
diff --git a/tests/run-make/branch-protection-check-IBT/main.rs b/tests/run-make/branch-protection-check-IBT/main.rs
index ad379d6ea43..445b8795134 100644
--- a/tests/run-make/branch-protection-check-IBT/main.rs
+++ b/tests/run-make/branch-protection-check-IBT/main.rs
@@ -1,3 +1,5 @@
-fn main() {
-    println!("hello world");
-}
+#![feature(no_core)]
+#![allow(internal_features)]
+#![no_core]
+#![no_std]
+#![no_main]
diff --git a/tests/run-make/branch-protection-check-IBT/rmake.rs b/tests/run-make/branch-protection-check-IBT/rmake.rs
new file mode 100644
index 00000000000..73109df12ae
--- /dev/null
+++ b/tests/run-make/branch-protection-check-IBT/rmake.rs
@@ -0,0 +1,53 @@
+// ignore-tidy-linelength
+//! A basic smoke test to check for GNU Property Note to see that for `x86_64` targets when [`-Z
+//! cf-protection=branch`][intel-cet-tracking-issue] is requested, that the
+//!
+//! ```text
+//! NT_GNU_PROPERTY_TYPE_0 Properties: x86 feature: IBT
+//! ```
+//!
+//! Intel Indirect Branch Tracking (IBT) property is emitted. This was generated in
+//! <https://github.com/rust-lang/rust/pull/110304> in order to address
+//! <https://github.com/rust-lang/rust/issues/103001>.
+//!
+//! Note that the precompiled std currently is not compiled with `-Z cf-protection=branch`!
+//!
+//! In particular, it is expected that:
+//!
+//! > IBT to only be enabled for the process if `.note.gnu.property` indicates that the executable
+//! > was compiled with IBT support and the linker to only tell that IBT is supported if all input
+//! > object files indicate that they support IBT, which in turn requires the standard library to be
+//! > compiled with IBT enabled.
+//!
+//! Note that Intel IBT (Indirect Branch Tracking) is not to be confused with Arm's BTI (Branch
+//! Target Identification). See below for link to Intel IBT docs.
+//!
+//! ## Related links
+//!
+//! - [Tracking Issue for Intel Control Enforcement Technology (CET)][intel-cet-tracking-issue]
+//! - Zulip question about this test:
+//! <https://rust-lang.zulipchat.com/#narrow/channel/182449-t-compiler.2Fhelp/topic/.E2.9C.94.20Branch.20protection.20and.20.60.2Enote.2Egnu.2Eproperty.60>
+//! - Intel IBT docs:
+//!   <https://edc.intel.com/content/www/us/en/design/ipla/software-development-platforms/client/platforms/alder-lake-desktop/12th-generation-intel-core-processors-datasheet-volume-1-of-2/006/indirect-branch-tracking/>
+//!
+//! [intel-cet-tracking-issue]: https://github.com/rust-lang/rust/issues/93754
+
+//@ needs-llvm-components: x86
+
+// FIXME(#93754): increase the test coverage of this test.
+//@ only-x86_64-unknown-linux-gnu
+//@ ignore-cross-compile
+
+use run_make_support::{bare_rustc, llvm_readobj};
+
+fn main() {
+    // `main.rs` is `#![no_std]` to not pull in the currently not-compiled-with-IBT precompiled std.
+    bare_rustc()
+        .input("main.rs")
+        .target("x86_64-unknown-linux-gnu")
+        .arg("-Zcf-protection=branch")
+        .arg("-Clink-args=-nostartfiles")
+        .run();
+
+    llvm_readobj().arg("-nW").input("main").run().assert_stdout_contains(".note.gnu.property");
+}