diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index 838a1681da..7c5e8e9ada 100644
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -22,6 +22,68 @@ TEXT _rt0_amd64(SB),NOSPLIT,$-8
 TEXT main(SB),NOSPLIT,$-8
 	JMP	runtime·rt0_go(SB)
 
+// _rt0_amd64_lib is common startup code for most amd64 systems when
+// using -buildmode=c-archive or -buildmode=c-shared. The linker will
+// arrange to invoke this function as a global constructor (for
+// c-archive) or when the shared library is loaded (for c-shared).
+// We expect argc and argv to be passed in the usual C ABI registers
+// DI and SI.
+TEXT _rt0_amd64_lib(SB),NOSPLIT,$0x50
+	// Align stack per ELF ABI requirements.
+	MOVQ	SP, AX
+	ANDQ	$~15, SP
+	// Save C ABI callee-saved registers, as caller may need them.
+	MOVQ	BX, 0x10(SP)
+	MOVQ	BP, 0x18(SP)
+	MOVQ	R12, 0x20(SP)
+	MOVQ	R13, 0x28(SP)
+	MOVQ	R14, 0x30(SP)
+	MOVQ	R15, 0x38(SP)
+	MOVQ	AX, 0x40(SP)
+
+	MOVQ	DI, _rt0_amd64_lib_argc<>(SB)
+	MOVQ	SI, _rt0_amd64_lib_argv<>(SB)
+
+	// Synchronous initialization.
+	CALL	runtime·libpreinit(SB)
+
+	// Create a new thread to finish Go runtime initialization.
+	MOVQ	_cgo_sys_thread_create(SB), AX
+	TESTQ	AX, AX
+	JZ	nocgo
+	MOVQ	$_rt0_amd64_lib_go(SB), DI
+	MOVQ	$0, SI
+	CALL	AX
+	JMP	restore
+
+nocgo:
+	MOVQ	$0x800000, 0(SP)		// stacksize
+	MOVQ	$_rt0_amd64_lib_go(SB), AX
+	MOVQ	AX, 8(SP)			// fn
+	CALL	runtime·newosproc0(SB)
+
+restore:
+	MOVQ	0x10(SP), BX
+	MOVQ	0x18(SP), BP
+	MOVQ	0x20(SP), R12
+	MOVQ	0x28(SP), R13
+	MOVQ	0x30(SP), R14
+	MOVQ	0x38(SP), R15
+	MOVQ	0x40(SP), SP
+	RET
+
+// _rt0_amd64_lib_go initializes the Go runtime.
+// This is started in a separate thread by _rt0_amd64_lib.
+TEXT _rt0_amd64_lib_go(SB),NOSPLIT,$0
+	MOVQ	_rt0_amd64_lib_argc<>(SB), DI
+	MOVQ	_rt0_amd64_lib_argv<>(SB), SI
+	JMP	runtime·rt0_go(SB)
+
+DATA _rt0_amd64_lib_argc<>(SB)/8, $0
+GLOBL _rt0_amd64_lib_argc<>(SB),NOPTR, $8
+DATA _rt0_amd64_lib_argv<>(SB)/8, $0
+GLOBL _rt0_amd64_lib_argv<>(SB),NOPTR, $8
+
 TEXT runtime·rt0_go(SB),NOSPLIT,$0
 	// copy arguments forward on an even stack
 	MOVQ	DI, AX		// argc
diff --git a/src/runtime/os_darwin.go b/src/runtime/os_darwin.go
index 15281674ae..635f71f126 100644
--- a/src/runtime/os_darwin.go
+++ b/src/runtime/os_darwin.go
@@ -135,7 +135,7 @@ func newosproc(mp *m, stk unsafe.Pointer) {
 // not safe to use after initialization as it does not pass an M as fnarg.
 //
 //go:nosplit
-func newosproc0(stacksize uintptr, fn unsafe.Pointer, fnarg uintptr) {
+func newosproc0(stacksize uintptr, fn uintptr) {
 	stack := sysAlloc(stacksize, &memstats.stacks_sys)
 	if stack == nil {
 		write(2, unsafe.Pointer(&failallocatestack[0]), int32(len(failallocatestack)))
@@ -145,7 +145,7 @@ func newosproc0(stacksize uintptr, fn unsafe.Pointer, fnarg uintptr) {
 
 	var oset sigset
 	sigprocmask(_SIG_SETMASK, &sigset_all, &oset)
-	errno := bsdthread_create(stk, fn, fnarg)
+	errno := bsdthread_create(stk, nil, fn)
 	sigprocmask(_SIG_SETMASK, &oset, nil)
 
 	if errno < 0 {
diff --git a/src/runtime/rt0_android_amd64.s b/src/runtime/rt0_android_amd64.s
index 3077cb1841..6bda3bfcc1 100644
--- a/src/runtime/rt0_android_amd64.s
+++ b/src/runtime/rt0_android_amd64.s
@@ -10,8 +10,7 @@ TEXT _rt0_amd64_android(SB),NOSPLIT,$-8
 TEXT _rt0_amd64_android_lib(SB),NOSPLIT,$0
 	MOVQ	$1, DI // argc
 	MOVQ	$_rt0_amd64_android_argv(SB), SI  // argv
-	MOVQ	$_rt0_amd64_linux_lib(SB), AX
-	JMP	AX
+	JMP	_rt0_amd64_lib(SB)
 
 DATA _rt0_amd64_android_argv+0x00(SB)/8,$_rt0_amd64_android_argv0(SB)
 DATA _rt0_amd64_android_argv+0x08(SB)/8,$0 // end argv
diff --git a/src/runtime/rt0_darwin_amd64.s b/src/runtime/rt0_darwin_amd64.s
index 2d11aa4155..ed804d47c5 100644
--- a/src/runtime/rt0_darwin_amd64.s
+++ b/src/runtime/rt0_darwin_amd64.s
@@ -9,64 +9,5 @@ TEXT _rt0_amd64_darwin(SB),NOSPLIT,$-8
 
 // When linking with -shared, this symbol is called when the shared library
 // is loaded.
-TEXT _rt0_amd64_darwin_lib(SB),NOSPLIT,$0x58
-	// Align stack. We don't know whether Go is adding a frame pointer here or not.
-	MOVQ	SP, R8
-	SUBQ	$16, R8
-	ANDQ	$~15, R8
-	XCHGQ	SP, R8
-
-	MOVQ	R8, 0x48(SP)
-	MOVQ	BX, 0x18(SP)
-	MOVQ	BP, 0x20(SP)
-	MOVQ	R12, 0x28(SP)
-	MOVQ	R13, 0x30(SP)
-	MOVQ	R14, 0x38(SP)
-	MOVQ	R15, 0x40(SP)
-
-	MOVQ	DI, _rt0_amd64_darwin_lib_argc<>(SB)
-	MOVQ	SI, _rt0_amd64_darwin_lib_argv<>(SB)
-
-	// Synchronous initialization.
-	MOVQ	$runtime·libpreinit(SB), AX
-	CALL	AX
-
-	// Create a new thread to do the runtime initialization and return.
-	MOVQ	_cgo_sys_thread_create(SB), AX
-	TESTQ	AX, AX
-	JZ	nocgo
-	MOVQ	$_rt0_amd64_darwin_lib_go(SB), DI
-	MOVQ	$0, SI
-	CALL	AX
-	JMP	restore
-
-nocgo:
-	MOVQ	$8388608, 0(SP)                    // stacksize
-	MOVQ	$_rt0_amd64_darwin_lib_go(SB), AX
-	MOVQ	AX, 8(SP)                          // fn
-	MOVQ	$0, 16(SP)                         // fnarg
-	MOVQ	$runtime·newosproc0(SB), AX
-	CALL	AX
-
-restore:
-	MOVQ	0x18(SP), BX
-	MOVQ	0x20(SP), BP
-	MOVQ	0x28(SP), R12
-	MOVQ	0x30(SP), R13
-	MOVQ	0x38(SP), R14
-	MOVQ	0x40(SP), R15
-	
-	MOVQ	0x48(SP), R8
-	MOVQ	R8, SP
-	RET
-
-TEXT _rt0_amd64_darwin_lib_go(SB),NOSPLIT,$0
-	MOVQ	_rt0_amd64_darwin_lib_argc<>(SB), DI
-	MOVQ	_rt0_amd64_darwin_lib_argv<>(SB), SI
-	MOVQ	$runtime·rt0_go(SB), AX
-	JMP	AX
-
-DATA _rt0_amd64_darwin_lib_argc<>(SB)/8, $0
-GLOBL _rt0_amd64_darwin_lib_argc<>(SB),NOPTR, $8
-DATA _rt0_amd64_darwin_lib_argv<>(SB)/8, $0
-GLOBL _rt0_amd64_darwin_lib_argv<>(SB),NOPTR, $8
+TEXT _rt0_amd64_darwin_lib(SB),NOSPLIT,$0
+	JMP	_rt0_amd64_lib(SB)
diff --git a/src/runtime/rt0_dragonfly_amd64.s b/src/runtime/rt0_dragonfly_amd64.s
index 166d3fafda..9f7a427d4d 100644
--- a/src/runtime/rt0_dragonfly_amd64.s
+++ b/src/runtime/rt0_dragonfly_amd64.s
@@ -6,3 +6,6 @@
 
 TEXT _rt0_amd64_dragonfly(SB),NOSPLIT,$-8
 	JMP	_rt0_amd64(SB)
+
+TEXT _rt0_amd64_dragonfly_lib(SB),NOSPLIT,$0
+	JMP	_rt0_amd64_lib(SB)
diff --git a/src/runtime/rt0_freebsd_amd64.s b/src/runtime/rt0_freebsd_amd64.s
index 5be2cd1301..ccc48f66b4 100644
--- a/src/runtime/rt0_freebsd_amd64.s
+++ b/src/runtime/rt0_freebsd_amd64.s
@@ -9,3 +9,6 @@ TEXT _rt0_amd64_freebsd(SB),NOSPLIT,$-8
 	LEAQ	8(DI), SI // argv
 	MOVQ	0(DI), DI // argc
 	JMP	runtime·rt0_go(SB)
+
+TEXT _rt0_amd64_freebsd_lib(SB),NOSPLIT,$0
+	JMP	_rt0_amd64_lib(SB)
diff --git a/src/runtime/rt0_linux_amd64.s b/src/runtime/rt0_linux_amd64.s
index 4faa1f24d3..94ff7094d6 100644
--- a/src/runtime/rt0_linux_amd64.s
+++ b/src/runtime/rt0_linux_amd64.s
@@ -7,61 +7,5 @@
 TEXT _rt0_amd64_linux(SB),NOSPLIT,$-8
 	JMP	_rt0_amd64(SB)
 
-// When building with -buildmode=c-shared, this symbol is called when the shared
-// library is loaded.
-// Note: This function calls external C code, which might required 16-byte stack
-// alignment after cmd/internal/obj applies its transformations.
-TEXT _rt0_amd64_linux_lib(SB),NOSPLIT,$0x50
-	MOVQ	SP, AX
-	ANDQ	$-16, SP
-	MOVQ	BX, 0x10(SP)
-	MOVQ	BP, 0x18(SP)
-	MOVQ	R12, 0x20(SP)
-	MOVQ	R13, 0x28(SP)
-	MOVQ	R14, 0x30(SP)
-	MOVQ	R15, 0x38(SP)
-	MOVQ	AX, 0x40(SP)
-
-	MOVQ	DI, _rt0_amd64_linux_lib_argc<>(SB)
-	MOVQ	SI, _rt0_amd64_linux_lib_argv<>(SB)
-
-	// Synchronous initialization.
-	MOVQ	$runtime·libpreinit(SB), AX
-	CALL	AX
-
-	// Create a new thread to do the runtime initialization and return.
-	MOVQ	_cgo_sys_thread_create(SB), AX
-	TESTQ	AX, AX
-	JZ	nocgo
-	MOVQ	$_rt0_amd64_linux_lib_go(SB), DI
-	MOVQ	$0, SI
-	CALL	AX
-	JMP	restore
-
-nocgo:
-	MOVQ	$8388608, 0(SP)                    // stacksize
-	MOVQ	$_rt0_amd64_linux_lib_go(SB), AX
-	MOVQ	AX, 8(SP)                          // fn
-	MOVQ	$runtime·newosproc0(SB), AX
-	CALL	AX
-
-restore:
-	MOVQ	0x10(SP), BX
-	MOVQ	0x18(SP), BP
-	MOVQ	0x20(SP), R12
-	MOVQ	0x28(SP), R13
-	MOVQ	0x30(SP), R14
-	MOVQ	0x38(SP), R15
-	MOVQ	0x40(SP), SP
-	RET
-
-TEXT _rt0_amd64_linux_lib_go(SB),NOSPLIT,$0
-	MOVQ	_rt0_amd64_linux_lib_argc<>(SB), DI
-	MOVQ	_rt0_amd64_linux_lib_argv<>(SB), SI
-	MOVQ	$runtime·rt0_go(SB), AX
-	JMP	AX
-
-DATA _rt0_amd64_linux_lib_argc<>(SB)/8, $0
-GLOBL _rt0_amd64_linux_lib_argc<>(SB),NOPTR, $8
-DATA _rt0_amd64_linux_lib_argv<>(SB)/8, $0
-GLOBL _rt0_amd64_linux_lib_argv<>(SB),NOPTR, $8
+TEXT _rt0_amd64_linux_lib(SB),NOSPLIT,$0
+	JMP	_rt0_amd64_lib(SB)
diff --git a/src/runtime/rt0_netbsd_amd64.s b/src/runtime/rt0_netbsd_amd64.s
index 7736c8d0aa..77c7187bba 100644
--- a/src/runtime/rt0_netbsd_amd64.s
+++ b/src/runtime/rt0_netbsd_amd64.s
@@ -6,3 +6,6 @@
 
 TEXT _rt0_amd64_netbsd(SB),NOSPLIT,$-8
 	JMP	_rt0_amd64(SB)
+
+TEXT _rt0_amd64_netbsd_lib(SB),NOSPLIT,$0
+	JMP	_rt0_amd64_lib(SB)
diff --git a/src/runtime/rt0_openbsd_amd64.s b/src/runtime/rt0_openbsd_amd64.s
index 6830a81cc2..c2f3f23f37 100644
--- a/src/runtime/rt0_openbsd_amd64.s
+++ b/src/runtime/rt0_openbsd_amd64.s
@@ -6,3 +6,6 @@
 
 TEXT _rt0_amd64_openbsd(SB),NOSPLIT,$-8
 	JMP	_rt0_amd64(SB)
+
+TEXT _rt0_amd64_openbsd_lib(SB),NOSPLIT,$0
+	JMP	_rt0_amd64_lib(SB)
diff --git a/src/runtime/rt0_solaris_amd64.s b/src/runtime/rt0_solaris_amd64.s
index 695b4a6c8e..5c46ded3ae 100644
--- a/src/runtime/rt0_solaris_amd64.s
+++ b/src/runtime/rt0_solaris_amd64.s
@@ -6,3 +6,6 @@
 
 TEXT _rt0_amd64_solaris(SB),NOSPLIT,$-8
 	JMP	_rt0_amd64(SB)
+
+TEXT _rt0_amd64_solaris_lib(SB),NOSPLIT,$0
+	JMP	_rt0_amd64_lib(SB)