Add profiling support, through the rustc -Z profile flag.

When -Z profile is passed, the GCDAProfiling LLVM pass is added
to the pipeline, which uses debug information to instrument the IR.
After compiling with -Z profile, the $(OUT_DIR)/$(CRATE_NAME).gcno
file is created, containing initial profiling information.
After running the program built, the $(OUT_DIR)/$(CRATE_NAME).gcda
file is created, containing branch counters.

The created *.gcno and *.gcda files can be processed using
the "llvm-cov gcov" and "lcov" tools. The profiling data LLVM
generates does not faithfully follow the GCC's format for *.gcno
and *.gcda files, and so it will probably not work with other tools
(such as gcov itself) that consume these files.

configure

@@ -452,6 +452,7 @@ opt vendor 0 "enable usage of vendored Rust crates"
 opt sanitizers 0 "build the sanitizer runtimes (asan, lsan, msan, tsan)"
 opt dist-src 1 "when building tarballs enables building a source tarball"
 opt cargo-openssl-static 0 "static openssl in cargo"
+opt profiler 0 "build the profiler runtime"
 
 # Optimization and debugging options. These may be overridden by the release channel, etc.
 opt_nosave optimize 1 "build optimized rust code"

src/Cargo.lock

@@ -355,6 +355,14 @@ dependencies = [
  "syntax_pos 0.0.0",
 ]
 
+[[package]]
+name = "profiler_builtins"
+version = "0.0.0"
+dependencies = [
+ "core 0.0.0",
+ "gcc 0.3.45 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [[package]]
 name = "pulldown-cmark"
 version = "0.0.8"
@@ -833,6 +841,7 @@ dependencies = [
  "libc 0.0.0",
  "panic_abort 0.0.0",
  "panic_unwind 0.0.0",
+ "profiler_builtins 0.0.0",
  "rand 0.0.0",
  "rustc_asan 0.0.0",
  "rustc_lsan 0.0.0",

src/bootstrap/check.rs

@@ -268,6 +268,10 @@ pub fn compiletest(build: &Build,
         cmd.env("SANITIZER_SUPPORT", "1");
     }
 
+    if build.config.profiler {
+        cmd.env("PROFILER_SUPPORT", "1");
+    }
+
     cmd.arg("--adb-path").arg("adb");
     cmd.arg("--adb-test-dir").arg(ADB_TEST_DIR);
     if target.contains("android") {

src/bootstrap/config.rs

@@ -50,6 +50,7 @@ pub struct Config {
     pub full_bootstrap: bool,
     pub extended: bool,
     pub sanitizers: bool,
+    pub profiler: bool,
 
     // llvm codegen options
     pub llvm_assertions: bool,
@@ -158,6 +159,7 @@ struct Build {
     extended: Option<bool>,
     verbose: Option<usize>,
     sanitizers: Option<bool>,
+    profiler: Option<bool>,
     openssl_static: Option<bool>,
 }
 
@@ -311,6 +313,7 @@ impl Config {
         set(&mut config.extended, build.extended);
         set(&mut config.verbose, build.verbose);
         set(&mut config.sanitizers, build.sanitizers);
+        set(&mut config.profiler, build.profiler);
         set(&mut config.openssl_static, build.openssl_static);
 
         if let Some(ref install) = toml.install {
@@ -462,6 +465,7 @@ impl Config {
                 ("FULL_BOOTSTRAP", self.full_bootstrap),
                 ("EXTENDED", self.extended),
                 ("SANITIZERS", self.sanitizers),
+                ("PROFILER", self.profiler),
                 ("DIST_SRC", self.rust_dist_src),
                 ("CARGO_OPENSSL_STATIC", self.openssl_static),
             }

src/bootstrap/config.toml.example

@@ -147,6 +147,9 @@
 # Build the sanitizer runtimes
 #sanitizers = false
 
+# Build the profiler runtime
+#profiler = false
+
 # Indicates whether the OpenSSL linked into Cargo will be statically linked or
 # not. If static linkage is specified then the build system will download a
 # known-good version of OpenSSL, compile it, and link it to Cargo.

src/bootstrap/lib.rs

@@ -667,6 +667,9 @@ impl Build {
         if self.config.backtrace {
             features.push_str(" backtrace");
         }
+        if self.config.profiler {
+            features.push_str(" profiler");
+        }
         return features
     }
 

src/doc/unstable-book/src/SUMMARY.md

@@ -2,6 +2,7 @@
 
 - [Compiler flags](compiler-flags.md)
     - [linker_flavor](compiler-flags/linker-flavor.md)
+    - [profile](compiler-flags/profile.md)
     - [remap_path_prefix](compiler-flags/remap-path-prefix.md)
 - [Language features](language-features.md)
     - [abi_msp430_interrupt](language-features/abi-msp430-interrupt.md)
@@ -71,6 +72,7 @@
     - [plugin_registrar](language-features/plugin-registrar.md)
     - [prelude_import](language-features/prelude-import.md)
     - [proc_macro](language-features/proc-macro.md)
+    - [profiler_runtime](language-features/profiler-runtime.md)
     - [quote](language-features/quote.md)
     - [relaxed_adts](language-features/relaxed-adts.md)
     - [repr_align](language-features/repr-align.md)
@@ -180,6 +182,7 @@
     - [print](library-features/print.md)
     - [proc_macro_internals](library-features/proc-macro-internals.md)
     - [process_try_wait](library-features/process-try-wait.md)
+    - [profiler_runtime_lib](library-features/sanitizer-runtime-lib.md)
     - [question_mark_carrier](library-features/question-mark-carrier.md)
     - [rand](library-features/rand.md)
     - [range_contains](library-features/range-contains.md)

src/doc/unstable-book/src/compiler-flags/profile.md

@@ -0,0 +1,5 @@
+# `profile`
+
+The tracking issue for this feature is: None
+
+------------------------

src/doc/unstable-book/src/language-features/profiler-runtime.md

@@ -0,0 +1,5 @@
+# `profiler_runtime`
+
+The tracking issue for this feature is: None.
+
+------------------------

src/doc/unstable-book/src/library-features/profiler-runtime-lib.md

@@ -0,0 +1,5 @@
+# `profiler_runtime_lib`
+
+This feature is internal to the Rust compiler and is not intended for general use.
+
+------------------------

src/libprofiler_builtins/Cargo.toml

@@ -0,0 +1,18 @@
+[package]
+authors = ["The Rust Project Developers"]
+build = "build.rs"
+name = "profiler_builtins"
+version = "0.0.0"
+
+[lib]
+name = "profiler_builtins"
+path = "lib.rs"
+test = false
+bench = false
+doc = false
+
+[dependencies]
+core = { path = "../libcore" }
+
+[build-dependencies]
+gcc = "0.3.27"

src/libprofiler_builtins/build.rs

@@ -0,0 +1,56 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+//! Compiles the profiler part of the `compiler-rt` library.
+//!
+//! See the build.rs for libcompiler_builtins crate for details.
+
+extern crate gcc;
+
+use std::env;
+use std::path::Path;
+
+fn main() {
+    let target = env::var("TARGET").expect("TARGET was not set");
+    let cfg = &mut gcc::Config::new();
+
+    if target.contains("msvc") {
+        // Don't pull in extra libraries on MSVC
+        cfg.flag("/Zl");
+    } else {
+        // Turn off various features of gcc and such, mostly copying
+        // compiler-rt's build system already
+        cfg.flag("-fno-builtin");
+        cfg.flag("-fvisibility=hidden");
+        cfg.flag("-fomit-frame-pointer");
+        cfg.flag("-ffreestanding");
+        cfg.define("VISIBILITY_HIDDEN", None);
+    }
+
+    let profile_sources = &["GCDAProfiling.c",
+                            "InstrProfiling.c",
+                            "InstrProfilingBuffer.c",
+                            "InstrProfilingFile.c",
+                            "InstrProfilingMerge.c",
+                            "InstrProfilingMergeFile.c",
+                            "InstrProfilingPlatformDarwin.c",
+                            "InstrProfilingPlatformLinux.c",
+                            "InstrProfilingPlatformOther.c",
+                            "InstrProfilingRuntime.cc",
+                            "InstrProfilingUtil.c",
+                            "InstrProfilingValue.c",
+                            "InstrProfilingWriter.c"];
+
+    for src in profile_sources {
+        cfg.file(Path::new("../compiler-rt/lib/profile").join(src));
+    }
+
+    cfg.compile("libprofiler-rt.a");
+}

src/libprofiler_builtins/lib.rs

@@ -0,0 +1,20 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![no_std]
+#![cfg_attr(not(stage0), feature(profiler_runtime))]
+#![cfg_attr(not(stage0), profiler_runtime)]
+#![unstable(feature = "profiler_runtime_lib",
+            reason = "internal implementation detail of rustc right now",
+            issue = "0")]
+#![crate_name = "profiler_builtins"]
+#![crate_type = "rlib"]
+#![allow(unused_features)]
+#![feature(staged_api)]

src/librustc/middle/cstore.rs

@@ -220,6 +220,7 @@ pub trait CrateStore {
     fn is_panic_runtime(&self, cnum: CrateNum) -> bool;
     fn is_compiler_builtins(&self, cnum: CrateNum) -> bool;
     fn is_sanitizer_runtime(&self, cnum: CrateNum) -> bool;
+    fn is_profiler_runtime(&self, cnum: CrateNum) -> bool;
     fn panic_strategy(&self, cnum: CrateNum) -> PanicStrategy;
     fn extern_crate(&self, cnum: CrateNum) -> Option<ExternCrate>;
     /// The name of the crate as it is referred to in source code of the current
@@ -356,6 +357,7 @@ impl CrateStore for DummyCrateStore {
     fn is_allocator(&self, cnum: CrateNum) -> bool { bug!("is_allocator") }
     fn is_panic_runtime(&self, cnum: CrateNum) -> bool { bug!("is_panic_runtime") }
     fn is_compiler_builtins(&self, cnum: CrateNum) -> bool { bug!("is_compiler_builtins") }
+    fn is_profiler_runtime(&self, cnum: CrateNum) -> bool { bug!("is_profiler_runtime") }
     fn is_sanitizer_runtime(&self, cnum: CrateNum) -> bool { bug!("is_sanitizer_runtime") }
     fn panic_strategy(&self, cnum: CrateNum) -> PanicStrategy {
         bug!("panic_strategy")

src/librustc/session/config.rs

@@ -1025,6 +1025,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "add a source pattern to the file path remapping config"),
     remap_path_prefix_to: Vec<String> = (vec![], parse_string_push, [TRACKED],
         "add a mapping target to the file path remapping config"),
+    profile: bool = (false, parse_bool, [TRACKED],
+                     "insert profiling code"),
 }
 
 pub fn default_lib_output() -> CrateType {

src/librustc_driver/driver.rs

@@ -203,7 +203,8 @@ pub fn compile_input(sess: &Session,
                 println!("Pre-trans");
                 tcx.print_debug_stats();
             }
-            let trans = phase_4_translate_to_llvm(tcx, analysis, &incremental_hashes_map);
+            let trans = phase_4_translate_to_llvm(tcx, analysis, &incremental_hashes_map,
+                                                  &outputs);
 
             if log_enabled!(::log::LogLevel::Info) {
                 println!("Post-trans");
@@ -1029,7 +1030,8 @@ pub fn phase_3_run_analysis_passes<'tcx, F, R>(sess: &'tcx Session,
 /// be discarded.
 pub fn phase_4_translate_to_llvm<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                                            analysis: ty::CrateAnalysis,
-                                           incremental_hashes_map: &IncrementalHashesMap)
+                                           incremental_hashes_map: &IncrementalHashesMap,
+                                           output_filenames: &OutputFilenames)
                                            -> trans::CrateTranslation {
     let time_passes = tcx.sess.time_passes();
 
@@ -1077,7 +1079,7 @@ pub fn phase_4_translate_to_llvm<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
     let translation =
         time(time_passes,
              "translation",
-             move || trans::trans_crate(tcx, analysis, &incremental_hashes_map));
+             move || trans::trans_crate(tcx, analysis, &incremental_hashes_map, output_filenames));
 
     time(time_passes,
          "assert dep graph",

src/librustc_llvm/ffi.rs

@@ -587,7 +587,9 @@ extern "C" {
     pub fn LLVMIsUndef(Val: ValueRef) -> Bool;
 
     // Operations on metadata
+    pub fn LLVMMDStringInContext(C: ContextRef, Str: *const c_char, SLen: c_uint) -> ValueRef;
     pub fn LLVMMDNodeInContext(C: ContextRef, Vals: *const ValueRef, Count: c_uint) -> ValueRef;
+    pub fn LLVMAddNamedMetadataOperand(M: ModuleRef, Name: *const c_char, Val: ValueRef);
 
     // Operations on scalar constants
     pub fn LLVMConstInt(IntTy: TypeRef, N: c_ulonglong, SignExtend: Bool) -> ValueRef;
@@ -1328,6 +1330,8 @@ extern "C" {
 
     pub fn LLVMRustAddModuleFlag(M: ModuleRef, name: *const c_char, value: u32);
 
+    pub fn LLVMRustMetadataAsValue(C: ContextRef, MD: MetadataRef) -> ValueRef;
+
     pub fn LLVMRustDIBuilderCreate(M: ModuleRef) -> DIBuilderRef;
 
     pub fn LLVMRustDIBuilderDispose(Builder: DIBuilderRef);

src/librustc_metadata/creader.rs

@@ -870,6 +870,33 @@ impl<'a> CrateLoader<'a> {
         }
     }
 
+    fn inject_profiler_runtime(&mut self) {
+        if self.sess.opts.debugging_opts.profile {
+            let mut uses_std = false;
+            self.cstore.iter_crate_data(|_, data| {
+                if data.name == "std" {
+                    uses_std = true;
+                }
+            });
+
+            if uses_std {
+                info!("loading profiler");
+
+                let symbol = Symbol::intern("profiler_builtins");
+                let dep_kind = DepKind::Implicit;
+                let (_, data) =
+                    self.resolve_crate(&None, symbol, symbol, None, DUMMY_SP,
+                                       PathKind::Crate, dep_kind);
+
+                // Sanity check the loaded crate to ensure it is indeed a profiler runtime
+                if !data.is_profiler_runtime() {
+                    self.sess.err(&format!("the crate `profiler_builtins` is not \
+                                            a profiler runtime"));
+                }
+            }
+        }
+    }
+
     fn inject_allocator_crate(&mut self) {
         // Make sure that we actually need an allocator, if none of our
         // dependencies need one then we definitely don't!
@@ -1071,6 +1098,7 @@ impl<'a> middle::cstore::CrateLoader for CrateLoader<'a> {
         // inject the sanitizer runtime before the allocator runtime because all
         // sanitizers force the use of the `alloc_system` allocator
         self.inject_sanitizer_runtime();
+        self.inject_profiler_runtime();
         self.inject_allocator_crate();
         self.inject_panic_runtime(krate);
 

src/librustc_metadata/cstore.rs

@@ -308,6 +308,11 @@ impl CrateMetadata {
         attr::contains_name(&attrs, "sanitizer_runtime")
     }
 
+    pub fn is_profiler_runtime(&self) -> bool {
+        let attrs = self.get_item_attrs(CRATE_DEF_INDEX);
+        attr::contains_name(&attrs, "profiler_runtime")
+    }
+
     pub fn is_no_builtins(&self) -> bool {
         let attrs = self.get_item_attrs(CRATE_DEF_INDEX);
         attr::contains_name(&attrs, "no_builtins")

src/librustc_metadata/cstore_impl.rs

@@ -275,6 +275,10 @@ impl CrateStore for cstore::CStore {
         self.get_crate_data(cnum).is_sanitizer_runtime()
     }
 
+    fn is_profiler_runtime(&self, cnum: CrateNum) -> bool {
+        self.get_crate_data(cnum).is_profiler_runtime()
+    }
+
     fn panic_strategy(&self, cnum: CrateNum) -> PanicStrategy {
         self.get_crate_data(cnum).panic_strategy()
     }

src/librustc_trans/back/link.rs

@@ -1074,6 +1074,9 @@ fn add_upstream_rust_crates(cmd: &mut Linker,
         // symbols from the dylib.
         let src = sess.cstore.used_crate_source(cnum);
         match data[cnum.as_usize() - 1] {
+            _ if sess.cstore.is_profiler_runtime(cnum) => {
+                add_static_crate(cmd, sess, tmpdir, crate_type, cnum);
+            }
             _ if sess.cstore.is_sanitizer_runtime(cnum) => {
                 link_sanitizer_runtime(cmd, sess, tmpdir, cnum);
             }

src/librustc_trans/back/write.rs

@@ -699,6 +699,10 @@ pub fn run_passes(sess: &Session,
         }
     }
 
+    if sess.opts.debugging_opts.profile {
+        modules_config.passes.push("insert-gcov-profiling".to_owned())
+    }
+
     modules_config.opt_level = Some(get_llvm_opt_level(sess.opts.optimize));
     modules_config.opt_size = Some(get_llvm_opt_size(sess.opts.optimize));
 

src/librustc_trans/base.rs

@@ -42,7 +42,7 @@ use rustc::dep_graph::AssertDepGraphSafe;
 use rustc::middle::cstore::LinkMeta;
 use rustc::hir::map as hir_map;
 use rustc::util::common::time;
-use session::config::{self, NoDebugInfo};
+use session::config::{self, NoDebugInfo, OutputFilenames};
 use rustc_incremental::IncrementalHashesMap;
 use session::{self, DataTypeKind, Session};
 use abi;
@@ -1053,7 +1053,8 @@ pub fn find_exported_symbols(tcx: TyCtxt, reachable: &NodeSet) -> NodeSet {
 
 pub fn trans_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
                              analysis: ty::CrateAnalysis,
-                             incremental_hashes_map: &IncrementalHashesMap)
+                             incremental_hashes_map: &IncrementalHashesMap,
+                             output_filenames: &OutputFilenames)
                              -> CrateTranslation {
     // Be careful with this krate: obviously it gives access to the
     // entire contents of the krate. So if you push any subtasks of
@@ -1070,7 +1071,8 @@ pub fn trans_crate<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 
     let shared_ccx = SharedCrateContext::new(tcx,
                                              exported_symbols,
-                                             check_overflow);
+                                             check_overflow,
+                                             output_filenames);
     // Translate the metadata.
     let (metadata_llcx, metadata_llmod, metadata) =
         time(tcx.sess.time_passes(), "write metadata", || {

src/librustc_trans/context.rs

@@ -27,6 +27,7 @@ use rustc::ty::subst::Substs;
 use rustc::ty::{self, Ty, TyCtxt};
 use rustc::ty::layout::{LayoutTyper, TyLayout};
 use session::config::NoDebugInfo;
+use session::config::OutputFilenames;
 use session::Session;
 use session::config;
 use util::nodemap::{NodeSet, DefIdMap, FxHashMap};
@@ -83,6 +84,8 @@ pub struct SharedCrateContext<'a, 'tcx: 'a> {
     check_overflow: bool,
 
     use_dll_storage_attrs: bool,
+
+    output_filenames: &'a OutputFilenames,
 }
 
 /// The local portion of a `CrateContext`.  There is one `LocalCrateContext`
@@ -266,7 +269,8 @@ pub unsafe fn create_context_and_module(sess: &Session, mod_name: &str) -> (Cont
 impl<'b, 'tcx> SharedCrateContext<'b, 'tcx> {
     pub fn new(tcx: TyCtxt<'b, 'tcx, 'tcx>,
                exported_symbols: NodeSet,
-               check_overflow: bool)
+               check_overflow: bool,
+               output_filenames: &'b OutputFilenames)
                -> SharedCrateContext<'b, 'tcx> {
         // An interesting part of Windows which MSVC forces our hand on (and
         // apparently MinGW didn't) is the usage of `dllimport` and `dllexport`
@@ -319,6 +323,7 @@ impl<'b, 'tcx> SharedCrateContext<'b, 'tcx> {
             tcx: tcx,
             check_overflow: check_overflow,
             use_dll_storage_attrs: use_dll_storage_attrs,
+            output_filenames: output_filenames,
         }
     }
 
@@ -353,6 +358,10 @@ impl<'b, 'tcx> SharedCrateContext<'b, 'tcx> {
     pub fn use_dll_storage_attrs(&self) -> bool {
         self.use_dll_storage_attrs
     }
+
+    pub fn output_filenames(&self) -> &OutputFilenames {
+        self.output_filenames
+    }
 }
 
 impl<'a, 'tcx> LocalCrateContext<'a, 'tcx> {

src/librustc_trans/debuginfo/metadata.rs

@@ -39,10 +39,12 @@ use rustc::ty::{self, AdtKind, Ty};
 use rustc::ty::layout::{self, LayoutTyper};
 use session::config;
 use util::nodemap::FxHashMap;
+use rustc::util::common::path2cstr;
 
 use libc::{c_uint, c_longlong};
 use std::ffi::CString;
 use std::ptr;
+use std::path::Path;
 use syntax::ast;
 use syntax::symbol::{Interner, InternedString, Symbol};
 use syntax_pos::{self, Span};
@@ -788,7 +790,7 @@ pub fn compile_unit_metadata(scc: &SharedCrateContext,
         let file_metadata = llvm::LLVMRustDIBuilderCreateFile(
             debug_context.builder, compile_unit_name, work_dir.as_ptr());
 
-        return llvm::LLVMRustDIBuilderCreateCompileUnit(
+        let unit_metadata = llvm::LLVMRustDIBuilderCreateCompileUnit(
             debug_context.builder,
             DW_LANG_RUST,
             file_metadata,
@@ -796,12 +798,46 @@ pub fn compile_unit_metadata(scc: &SharedCrateContext,
             sess.opts.optimize != config::OptLevel::No,
             flags.as_ptr() as *const _,
             0,
-            split_name.as_ptr() as *const _)
+            split_name.as_ptr() as *const _);
+
+        let cu_desc_metadata = llvm::LLVMRustMetadataAsValue(debug_context.llcontext,
+                                                             unit_metadata);
+
+        let gcov_cu_info = [
+            // Ideally we would be using the three-element form of !llvm.gcov metadata,
+            // which allows us to specify gcno/gcda files explicitly, but that's only
+            // available in LLVM 3.9+; so we rely on LLVM chopping off the extension
+            // and replacing it with gcno/gcda, instead.
+            path_to_mdstring(debug_context.llcontext,
+                             &scc.output_filenames().with_extension("gcno")),
+            // path_to_mdstring(debug_context.llcontext,
+            //                  &scc.output_filenames().with_extension("gcda")),
+            cu_desc_metadata,
+        ];
+        let gcov_metadata = llvm::LLVMMDNodeInContext(debug_context.llcontext,
+                                                      gcov_cu_info.as_ptr(),
+                                                      gcov_cu_info.len() as c_uint);
+
+        let llvm_gcov_ident = CString::new("llvm.gcov").unwrap();
+        llvm::LLVMAddNamedMetadataOperand(debug_context.llmod,
+                                          llvm_gcov_ident.as_ptr(),
+                                          gcov_metadata);
+
+        return unit_metadata;
     };
 
     fn fallback_path(scc: &SharedCrateContext) -> CString {
         CString::new(scc.tcx().crate_name(LOCAL_CRATE).to_string()).unwrap()
     }
+
+    fn path_to_mdstring(llcx: llvm::ContextRef, path: &Path) -> llvm::ValueRef {
+        let path_str = path2cstr(path);
+        unsafe {
+            llvm::LLVMMDStringInContext(llcx,
+                                        path_str.as_ptr(),
+                                        path_str.as_bytes().len() as c_uint)
+        }
+    }
 }
 
 struct MetadataCreationResult {

src/librustc_trans/debuginfo/mod.rs

@@ -67,6 +67,7 @@ const DW_TAG_arg_variable: c_uint = 0x101;
 /// A context object for maintaining all state needed by the debuginfo module.
 pub struct CrateDebugContext<'tcx> {
     llcontext: ContextRef,
+    llmod: ModuleRef,
     builder: DIBuilderRef,
     created_files: RefCell<FxHashMap<(Symbol, Symbol), DIFile>>,
     created_enum_disr_types: RefCell<FxHashMap<(DefId, layout::Integer), DIType>>,
@@ -87,6 +88,7 @@ impl<'tcx> CrateDebugContext<'tcx> {
         let llcontext = unsafe { llvm::LLVMGetModuleContext(llmod) };
         CrateDebugContext {
             llcontext: llcontext,
+            llmod: llmod,
             builder: builder,
             created_files: RefCell::new(FxHashMap()),
             created_enum_disr_types: RefCell::new(FxHashMap()),

src/libstd/Cargo.toml

@@ -20,6 +20,7 @@ core = { path = "../libcore" }
 libc = { path = "../rustc/libc_shim" }
 rand = { path = "../librand" }
 compiler_builtins = { path = "../libcompiler_builtins" }
+profiler_builtins = { path = "../libprofiler_builtins", optional = true }
 std_unicode = { path = "../libstd_unicode" }
 unwind = { path = "../libunwind" }
 
@@ -43,3 +44,4 @@ debug-jemalloc = ["alloc_jemalloc/debug"]
 jemalloc = ["alloc_jemalloc"]
 force_alloc_system = []
 panic-unwind = ["panic_unwind"]
+profiler = ["profiler_builtins"]

src/libsyntax/feature_gate.rs

@@ -331,6 +331,10 @@ declare_features! (
     // rustc internal
     (active, sanitizer_runtime, "1.17.0", None),
 
+    // Used to identify crates that contain the profiler runtime
+    // rustc internal
+    (active, profiler_runtime, "1.18.0", None),
+
     // `extern "x86-interrupt" fn()`
     (active, abi_x86_interrupt, "1.17.0", Some(40180)),
 
@@ -693,6 +697,13 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                               identify crates that contain the runtime of a \
                                               sanitizer and will never be stable",
                                              cfg_fn!(sanitizer_runtime))),
+    ("profiler_runtime", Whitelisted, Gated(Stability::Unstable,
+                                             "profiler_runtime",
+                                             "the `#[profiler_runtime]` attribute is used to \
+                                              identify the `profiler_builtins` crate which \
+                                              contains the profiler runtime and will never be \
+                                              stable",
+                                             cfg_fn!(profiler_runtime))),
 
     ("allow_internal_unstable", Normal, Gated(Stability::Unstable,
                                               "allow_internal_unstable",

src/rustllvm/RustWrapper.cpp

@@ -466,6 +466,10 @@ extern "C" void LLVMRustAddModuleFlag(LLVMModuleRef M, const char *Name,
   unwrap(M)->addModuleFlag(Module::Warning, Name, Value);
 }
 
+extern "C" void LLVMRustMetadataAsValue(LLVMContextRef C, LLVMRustMetadataRef MD) {
+  wrap(MetadataAsValue::get(*unwrap(C), unwrap(MD)));
+}
+
 extern "C" LLVMRustDIBuilderRef LLVMRustDIBuilderCreate(LLVMModuleRef M) {
   return new DIBuilder(*unwrap(M));
 }

src/test/compile-fail/feature-gate-profiler-runtime.rs

@@ -0,0 +1,13 @@
+// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+#![profiler_runtime] //~ ERROR the `#[profiler_runtime]` attribute is
+
+fn main() {}

src/test/run-make/profile/Makefile

@@ -0,0 +1,7 @@
+-include ../tools.mk
+
+all:
+	$(RUSTC) -g -Z profile test.rs
+	$(call RUN,test) || exit 1
+	[ -e "$(TMPDIR)/test.gcno" ] || (echo "No .gcno file"; exit 1)
+	[ -e "$(TMPDIR)/test.gcda" ] || (echo "No .gcda file"; exit 1)

src/test/run-make/profile/test.rs

@@ -0,0 +1,11 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn main() {}