Auto merge of #102963 - ilammy:xray-basic, r=estebank

Add `-Z instrument-xray` flag

Implement MCP https://github.com/rust-lang/compiler-team/issues/561, adding `-Z instrument-xray` flag which enables XRay instrumentation in LLVM.

4 files changed, 55 insertions, 1 deletions

diff --git a/src/doc/unstable-book/src/compiler-flags/instrument-xray.md b/src/doc/unstable-book/src/compiler-flags/instrument-xray.md
new file mode 100644
index 00000000000..7fb33cd68b4
--- /dev/null
+++ b/src/doc/unstable-book/src/compiler-flags/instrument-xray.md
@@ -0,0 +1,39 @@
+# `instrument-xray`
+
+The tracking issue for this feature is: [#102921](https://github.com/rust-lang/rust/issues/102921).
+
+------------------------
+
+Enable generation of NOP sleds for XRay function tracing instrumentation.
+For more information on XRay,
+read [LLVM documentation](https://llvm.org/docs/XRay.html),
+and/or the [XRay whitepaper](http://research.google.com/pubs/pub45287.html).
+
+Set the `-Z instrument-xray` compiler flag in order to enable XRay instrumentation.
+
+  - `-Z instrument-xray` – use the default settings
+  - `-Z instrument-xray=skip-exit` – configure a custom setting
+  - `-Z instrument-xray=ignore-loops,instruction-threshold=300` –
+    multiple settings separated by commas
+
+Supported options:
+
+  - `always` – force instrumentation of all functions
+  - `never` – do no instrument any functions
+  - `ignore-loops` – ignore presence of loops,
+    instrument functions based only on instruction count
+  - `instruction-threshold=10` – set a different instruction threshold for instrumentation
+  - `skip-entry` – do no instrument function entry
+  - `skip-exit` – do no instrument function exit
+
+The default settings are:
+
+  - instrument both entry & exit from functions
+  - instrument functions with at least 200 instructions,
+    or containing a non-trivial loop
+
+Note that `-Z instrument-xray` only enables generation of NOP sleds
+which on their own don't do anything useful.
+In order to actually trace the functions,
+you will need to link a separate runtime library of your choice,
+such as Clang's [XRay Runtime Library](https://www.llvm.org/docs/XRay.html#xray-runtime-library).
diff --git a/src/tools/compiletest/src/header.rs b/src/tools/compiletest/src/header.rs
index 45fd87bea9b..e11ebca6ea9 100644
--- a/src/tools/compiletest/src/header.rs
+++ b/src/tools/compiletest/src/header.rs
@@ -941,6 +941,7 @@ pub fn make_test_description<R: Read>(
     let has_hwasan = util::HWASAN_SUPPORTED_TARGETS.contains(&&*config.target);
     let has_memtag = util::MEMTAG_SUPPORTED_TARGETS.contains(&&*config.target);
     let has_shadow_call_stack = util::SHADOWCALLSTACK_SUPPORTED_TARGETS.contains(&&*config.target);
+    let has_xray = util::XRAY_SUPPORTED_TARGETS.contains(&&*config.target);
 
     // For tests using the `needs-rust-lld` directive (e.g. for `-Zgcc-ld=lld`), we need to find
     // whether `rust-lld` is present in the compiler under test.
@@ -1019,6 +1020,7 @@ pub fn make_test_description<R: Read>(
                 && config.parse_name_directive(ln, "needs-sanitizer-shadow-call-stack")
         );
         reason!(!config.can_unwind() && config.parse_name_directive(ln, "needs-unwind"));
+        reason!(!has_xray && config.parse_name_directive(ln, "needs-xray"));
         reason!(
             config.target == "wasm32-unknown-unknown"
                 && config.parse_name_directive(ln, directives::CHECK_RUN_RESULTS)
diff --git a/src/tools/compiletest/src/util.rs b/src/tools/compiletest/src/util.rs
index ff7e8df9878..67f49bb6397 100644
--- a/src/tools/compiletest/src/util.rs
+++ b/src/tools/compiletest/src/util.rs
@@ -78,6 +78,19 @@ pub const MEMTAG_SUPPORTED_TARGETS: &[&str] =
 
 pub const SHADOWCALLSTACK_SUPPORTED_TARGETS: &[&str] = &["aarch64-linux-android"];
 
+pub const XRAY_SUPPORTED_TARGETS: &[&str] = &[
+    "aarch64-linux-android",
+    "aarch64-unknown-linux-gnu",
+    "aarch64-unknown-linux-musl",
+    "x86_64-linux-android",
+    "x86_64-unknown-freebsd",
+    "x86_64-unknown-linux-gnu",
+    "x86_64-unknown-linux-musl",
+    "x86_64-unknown-netbsd",
+    "x86_64-unknown-none-linuxkernel",
+    "x86_64-unknown-openbsd",
+];
+
 pub fn make_new_path(path: &str) -> String {
     assert!(cfg!(windows));
     // Windows just uses PATH as the library search path, so we have to
diff --git a/src/tools/tidy/src/ui_tests.rs b/src/tools/tidy/src/ui_tests.rs
index 83551a1d820..ef3abb9514f 100644
--- a/src/tools/tidy/src/ui_tests.rs
+++ b/src/tools/tidy/src/ui_tests.rs
@@ -9,7 +9,7 @@ use std::path::Path;
 
 const ENTRY_LIMIT: usize = 1000;
 // FIXME: The following limits should be reduced eventually.
-const ROOT_ENTRY_LIMIT: usize = 939;
+const ROOT_ENTRY_LIMIT: usize = 940;
 const ISSUES_ENTRY_LIMIT: usize = 2001;
 
 fn check_entries(path: &Path, bad: &mut bool) {