Emit DW_AT_main_subprogram

This changes rustc to emit DW_AT_main_subprogram on the "main" program.
This lets gdb suitably stop at the user's main in response to
"start" (rather than the library's main, which is what happens
currently).

Fixes #32620
r? michaelwoerister

2 files changed, 56 insertions, 0 deletions

diff --git a/src/test/codegen/mainsubprogram.rs b/src/test/codegen/mainsubprogram.rs
new file mode 100644
index 00000000000..657f4b662f7
--- /dev/null
+++ b/src/test/codegen/mainsubprogram.rs
@@ -0,0 +1,26 @@
+// 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.
+
+// The minimum LLVM version is set to 3.8, but really this test
+// depends on a patch that is was committed to upstream LLVM before
+// 4.0; and also backported to the Rust LLVM fork.
+
+// ignore-tidy-linelength
+// ignore-windows
+// ignore-macos
+// min-llvm-version 3.8
+
+// compile-flags: -g -C no-prepopulate-passes
+
+// CHECK-LABEL: @main
+// CHECK: {{.*}}DISubprogram{{.*}}name: "main",{{.*}}DIFlagMainSubprogram{{.*}}
+
+pub fn main() {
+}
diff --git a/src/test/codegen/mainsubprogramstart.rs b/src/test/codegen/mainsubprogramstart.rs
new file mode 100644
index 00000000000..cd34a1670dc
--- /dev/null
+++ b/src/test/codegen/mainsubprogramstart.rs
@@ -0,0 +1,30 @@
+// 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.
+
+// The minimum LLVM version is set to 3.8, but really this test
+// depends on a patch that is was committed to upstream LLVM before
+// 4.0; and also backported to the Rust LLVM fork.
+
+// ignore-tidy-linelength
+// ignore-windows
+// ignore-macos
+// min-llvm-version 3.8
+
+// compile-flags: -g -C no-prepopulate-passes
+
+#![feature(start)]
+
+// CHECK-LABEL: @main
+// CHECK: {{.*}}DISubprogram{{.*}}name: "start",{{.*}}DIFlagMainSubprogram{{.*}}
+
+#[start]
+fn start(_: isize, _: *const *const u8) -> isize {
+    return 0;
+}