runtime: initialize shared library at library-load time

This is Part 2 of the change, see Part 1 here: in https://go-review.googlesource.com/#/c/7692/

Suggested by iant@, we use the library initialization entry point to:
    - create a new OS thread and run the "regular" runtime init stack on
      that thread
    - return immediately from the main (i.e., loader) thread
    - at the first CGO invocation, we wait for the runtime initialization
      to complete.

The above mechanism is implemented only on linux_amd64.  Next step is to
support it on linux_arm.  Other platforms don't yet support shared library
compiling/linking, but we intend to use the same strategy there as well.

Change-Id: Ib2c81b1b83bee837134084b75a3beecfb8de6bf4
Reviewed-on: https://go-review.googlesource.com/8094
Run-TryBot: Srdjan Petrovic <spetrovic@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

1 files changed, 8 insertions, 4 deletions

diff --git a/src/runtime/cgo.go b/src/runtime/cgo.go
index 5dc83c0be1..d8ae6ec94b 100644
--- a/src/runtime/cgo.go
+++ b/src/runtime/cgo.go
@@ -14,12 +14,16 @@ import "unsafe"
 //go:linkname _cgo_malloc _cgo_malloc
 //go:linkname _cgo_free _cgo_free
 //go:linkname _cgo_thread_start _cgo_thread_start
+//go:linkname _cgo_sys_thread_create _cgo_sys_thread_create
+//go:linkname _cgo_notify_runtime_init_done _cgo_notify_runtime_init_done
 
 var (
-	_cgo_init         unsafe.Pointer
-	_cgo_malloc       unsafe.Pointer
-	_cgo_free         unsafe.Pointer
-	_cgo_thread_start unsafe.Pointer
+	_cgo_init                     unsafe.Pointer
+	_cgo_malloc                   unsafe.Pointer
+	_cgo_free                     unsafe.Pointer
+	_cgo_thread_start             unsafe.Pointer
+	_cgo_sys_thread_create        unsafe.Pointer
+	_cgo_notify_runtime_init_done unsafe.Pointer
 )
 
 // iscgo is set to true by the runtime/cgo package