runtime: fix AIX library initialization

On AIX, libInit passes a function descriptor instead of the function
pointer to pthread_create. This is a regression from CL 706417.

Change-Id: I660175eb992a41ef61b1927c51392887a724cd76
Reviewed-on: https://go-review.googlesource.com/c/go/+/761780
Reviewed-by: Ian Lance Taylor <iant@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: David Chase <drchase@google.com>

1 files changed, 16 insertions, 2 deletions

diff --git a/src/runtime/libinit.go b/src/runtime/libinit.go
index 7e298a2eca..2c81f61644 100644
--- a/src/runtime/libinit.go
+++ b/src/runtime/libinit.go
@@ -11,6 +11,13 @@ import (
 	"unsafe"
 )
 
+// rt0LibGoFn holds the function pointer to rt0_lib_go suitable for thread
+// creation. On most platforms it is zero, meaning the raw code address should
+// be used. On AIX it is set by libpreinit to a function descriptor pointer,
+// because pthread_create on AIX expects a function descriptor, not a raw
+// code address.
+var rt0LibGoFn uintptr
+
 // libInit is common startup code for most architectures when
 // using -buildmode=c-archive or -buildmode=c-shared.
 //
@@ -22,13 +29,20 @@ func libInit() {
 	// Synchronous initialization.
 	libpreinit()
 
+	// Use the platform-specific function pointer if set (e.g. AIX
+	// function descriptor), otherwise fall back to the raw code address.
+	fn := unsafe.Pointer(rt0LibGoFn)
+	if fn == nil {
+		fn = unsafe.Pointer(abi.FuncPCABIInternal(rt0_lib_go))
+	}
+
 	// Asynchronous initialization.
 	// Prefer creating a thread via cgo if it is available.
 	if _cgo_sys_thread_create != nil {
 		// No g because the TLS is not set up until later in rt0_go.
-		asmcgocall_no_g(_cgo_sys_thread_create, unsafe.Pointer(abi.FuncPCABIInternal(rt0_lib_go)))
+		asmcgocall_no_g(_cgo_sys_thread_create, fn)
 	} else {
 		const stackSize = 0x800000 // 8192KB
-		newosproc0(stackSize, unsafe.Pointer(abi.FuncPCABIInternal(rt0_lib_go)))
+		newosproc0(stackSize, fn)
 	}
 }