Rollup merge of #39400 - alexcrichton:arm-cross-test, r=brson

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

1 files changed, 11 insertions, 0 deletions

diff --git a/src/bootstrap/lib.rs b/src/bootstrap/lib.rs
index df1218752d1..e58dcc9fce9 100644
--- a/src/bootstrap/lib.rs
+++ b/src/bootstrap/lib.rs
@@ -878,6 +878,17 @@ impl Build {
             .map(|p| &**p)
     }
 
+    /// Returns the root of the "rootfs" image that this target will be using,
+    /// if one was configured.
+    ///
+    /// If `Some` is returned then that means that tests for this target are
+    /// emulated with QEMU and binaries will need to be shipped to the emulator.
+    fn qemu_rootfs(&self, target: &str) -> Option<&Path> {
+        self.config.target_config.get(target)
+            .and_then(|t| t.qemu_rootfs.as_ref())
+            .map(|p| &**p)
+    }
+
     /// Path to the python interpreter to use
     fn python(&self) -> &Path {
         self.config.python.as_ref().unwrap()