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>

3 files changed, 32 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)
 	}
 }
diff --git a/src/runtime/os_aix.go b/src/runtime/os_aix.go
index 7a667c2419..bf78869328 100644
--- a/src/runtime/os_aix.go
+++ b/src/runtime/os_aix.go
@@ -162,6 +162,10 @@ func newosproc0(stacksize uintptr, fn unsafe.Pointer) {
 //go:nosplit
 //go:nowritebarrierrec
 func libpreinit() {
+	// On AIX, pthread_create expects a function descriptor pointer,
+	// not a raw code address. Set rt0LibGoFn to the descriptor
+	// so that libInit passes the right value.
+	rt0LibGoFn = uintptr(unsafe.Pointer(&rt0LibGoDesc))
 	initsig(true)
 }
 
@@ -203,6 +207,9 @@ func mdestroy(mp *m) {
 // tstart is a function descriptor to _tstart defined in assembly.
 var tstart funcDescriptor
 
+// rt0LibGoDesc is a function descriptor to rt0_lib_go defined in assembly.
+var rt0LibGoDesc funcDescriptor
+
 func newosproc(mp *m) {
 	var (
 		attr pthread_attr
diff --git a/src/runtime/sys_aix_ppc64.s b/src/runtime/sys_aix_ppc64.s
index a0ef7e111a..41a4fa330c 100644
--- a/src/runtime/sys_aix_ppc64.s
+++ b/src/runtime/sys_aix_ppc64.s
@@ -197,6 +197,15 @@ DATA	runtime·tstart+8(SB)/8, $TOC(SB)
 DATA	runtime·tstart+16(SB)/8, $0
 GLOBL	runtime·tstart(SB), NOPTR, $24
 
+// runtime.rt0LibGoDesc is a function descriptor to rt0_lib_go,
+// used by libInit to create a new thread on AIX where
+// pthread_create expects a function descriptor, not a raw
+// code address.
+DATA	runtime·rt0LibGoDesc+0(SB)/8, $runtime·rt0_lib_go(SB)
+DATA	runtime·rt0LibGoDesc+8(SB)/8, $TOC(SB)
+DATA	runtime·rt0LibGoDesc+16(SB)/8, $0
+GLOBL	runtime·rt0LibGoDesc(SB), NOPTR, $24
+
 TEXT tstart<>(SB),NOSPLIT,$0
 	XOR	 R0, R0 // reset R0