rustc: Support auto-retry linking on a segfault

.travis.yml

@@ -44,6 +44,7 @@ matrix:
         RUST_CHECK_TARGET=check
         RUST_CONFIGURE_ARGS=--build=x86_64-apple-darwin
         SRC=.
+        RUSTC_RETRY_LINKER_ON_SEGFAULT=1
       os: osx
       osx_image: xcode8.2
       install: &osx_install_sccache >
@@ -53,6 +54,7 @@ matrix:
         RUST_CHECK_TARGET=check
         RUST_CONFIGURE_ARGS=--build=i686-apple-darwin
         SRC=.
+        RUSTC_RETRY_LINKER_ON_SEGFAULT=1
       os: osx
       osx_image: xcode8.2
       install: *osx_install_sccache
@@ -62,6 +64,7 @@ matrix:
         RUST_CONFIGURE_ARGS="--build=i686-apple-darwin --enable-extended"
         SRC=.
         DEPLOY=1
+        RUSTC_RETRY_LINKER_ON_SEGFAULT=1
       os: osx
       osx_image: xcode8.2
       install: >
@@ -74,6 +77,7 @@ matrix:
         RUST_CONFIGURE_ARGS="--target=aarch64-apple-ios,armv7-apple-ios,armv7s-apple-ios,i386-apple-ios,x86_64-apple-ios --enable-extended"
         SRC=.
         DEPLOY=1
+        RUSTC_RETRY_LINKER_ON_SEGFAULT=1
       os: osx
       osx_image: xcode8.2
       install: *osx_install_sccache
@@ -88,6 +92,7 @@ matrix:
         RUST_CONFIGURE_ARGS="--enable-extended"
         SRC=.
         DEPLOY_ALT=1
+        RUSTC_RETRY_LINKER_ON_SEGFAULT=1
       os: osx
       osx_image: xcode8.2
       install: *osx_install_sccache

src/librustc_trans/back/link.rs

@@ -752,8 +752,54 @@ fn link_natively(sess: &Session,
     sess.abort_if_errors();
 
     // Invoke the system linker
+    //
+    // Note that there's a terribly awful hack that really shouldn't be present
+    // in any compiler. Here an environment variable is supported to
+    // automatically retry the linker invocation if the linker looks like it
+    // segfaulted.
+    //
+    // Gee that seems odd, normally segfaults are things we want to know about!
+    // Unfortunately though in rust-lang/rust#38878 we're experiencing the
+    // linker segfaulting on Travis quite a bit which is causing quite a bit of
+    // pain to land PRs when they spuriously fail due to a segfault.
+    //
+    // The issue #38878 has some more debugging information on it as well, but
+    // this unfortunately looks like it's just a race condition in OSX's linker
+    // with some thread pool working in the background. It seems that no one
+    // currently knows a fix for this so in the meantime we're left with this...
     info!("{:?}", &cmd);
-    let prog = time(sess.time_passes(), "running linker", || cmd.output());
+    let retry_on_segfault = env::var("RUSTC_RETRY_LINKER_ON_SEGFAULT").is_ok();
+    let mut prog;
+    let mut i = 0;
+    loop {
+        i += 1;
+        prog = time(sess.time_passes(), "running linker", || cmd.output());
+        if !retry_on_segfault || i > 3 {
+            break
+        }
+        let output = match prog {
+            Ok(ref output) => output,
+            Err(_) => break,
+        };
+        if output.status.success() {
+            break
+        }
+        let mut out = output.stderr.clone();
+        out.extend(&output.stdout);
+        let out = String::from_utf8_lossy(&out);
+        let msg = "clang: error: unable to execute command: \
+                   Segmentation fault: 11";
+        if !out.contains(msg) {
+            break
+        }
+
+        sess.struct_warn("looks like the linker segfaulted when we tried to \
+                          call it, automatically retrying again")
+            .note(&format!("{:?}", cmd))
+            .note(&out)
+            .emit();
+    }
+
     match prog {
         Ok(prog) => {
             fn escape_string(s: &[u8]) -> String {