Add support for test suites emulated in QEMU

This commit adds support to the build system to execute test suites that cannot
run natively but can instead run inside of a QEMU emulator. A proof-of-concept
builder was added for the `arm-unknown-linux-gnueabihf` target to show off how
this might work.

In general the architecture is to have a server running inside of the emulator
which a local client connects to. The protocol between the server/client
supports compiling tests on the host and running them on the target inside the
emulator.

Closes #33114

src/tools/compiletest/src/common.rs

@@ -185,6 +185,9 @@ pub struct Config {
     // Print one character per test instead of one line
     pub quiet: bool,
 
+    // where to find the qemu test client process, if we're using it
+    pub qemu_test_client: Option<PathBuf>,
+
     // Configuration for various run-make tests frobbing things like C compilers
     // or querying about various LLVM component information.
     pub cc: String,

src/tools/compiletest/src/main.rs

@@ -116,6 +116,7 @@ pub fn parse_config(args: Vec<String> ) -> Config {
           reqopt("", "llvm-components", "list of LLVM components built in", "LIST"),
           reqopt("", "llvm-cxxflags", "C++ flags for LLVM", "FLAGS"),
           optopt("", "nodejs", "the name of nodejs", "PATH"),
+          optopt("", "qemu-test-client", "path to the qemu test client", "PATH"),
           optflag("h", "help", "show this message")];
 
     let (argv0, args_) = args.split_first().unwrap();
@@ -196,6 +197,7 @@ pub fn parse_config(args: Vec<String> ) -> Config {
         lldb_python_dir: matches.opt_str("lldb-python-dir"),
         verbose: matches.opt_present("verbose"),
         quiet: matches.opt_present("quiet"),
+        qemu_test_client: matches.opt_str("qemu-test-client").map(PathBuf::from),
 
         cc: matches.opt_str("cc").unwrap(),
         cxx: matches.opt_str("cxx").unwrap(),
@@ -302,6 +304,14 @@ pub fn run_tests(config: &Config) {
             // time.
             env::set_var("RUST_TEST_THREADS", "1");
         }
+
+        DebugInfoGdb => {
+            if config.qemu_test_client.is_some() {
+                println!("WARNING: debuginfo tests are not available when \
+                          testing with QEMU");
+                return
+            }
+        }
         _ => { /* proceed */ }
     }
 

src/tools/compiletest/src/runtest.rs

@@ -1190,7 +1190,45 @@ actual:\n\
             "arm-linux-androideabi" | "armv7-linux-androideabi" | "aarch64-linux-android" => {
                 self._arm_exec_compiled_test(env)
             }
-            _=> {
+
+            // This is pretty similar to below, we're transforming:
+            //
+            //      program arg1 arg2
+            //
+            // into
+            //
+            //      qemu-test-client run program:support-lib.so arg1 arg2
+            //
+            // The test-client program will upload `program` to the emulator
+            // along with all other support libraries listed (in this case
+            // `support-lib.so`. It will then execute the program on the
+            // emulator with the arguments specified (in the environment we give
+            // the process) and then report back the same result.
+            _ if self.config.qemu_test_client.is_some() => {
+                let aux_dir = self.aux_output_dir_name();
+                let mut args = self.make_run_args();
+                let mut program = args.prog.clone();
+                if let Ok(entries) = aux_dir.read_dir() {
+                    for entry in entries {
+                        let entry = entry.unwrap();
+                        if !entry.path().is_file() {
+                            continue
+                        }
+                        program.push_str(":");
+                        program.push_str(entry.path().to_str().unwrap());
+                    }
+                }
+                args.args.insert(0, program);
+                args.args.insert(0, "run".to_string());
+                args.prog = self.config.qemu_test_client.clone().unwrap()
+                                .into_os_string().into_string().unwrap();
+                self.compose_and_run(args,
+                                     env,
+                                     self.config.run_lib_path.to_str().unwrap(),
+                                     Some(aux_dir.to_str().unwrap()),
+                                     None)
+            }
+            _ => {
                 let aux_dir = self.aux_output_dir_name();
                 self.compose_and_run(self.make_run_args(),
                                      env,