runtime: make it possible to call syscall on solaris without g

The nosplit stack is now much bigger, so we can afford to allocate
libcall on stack.

Fix asmsysvicall6 to not update errno if g == nil.

These two fixes TestCgoCallbackGC on solaris, which used to stuck
in a loop.

Change-Id: Id1b13be992dae9f059aa3d47ffffd37785300933
Reviewed-on: https://go-review.googlesource.com/17076
Run-TryBot: Minux Ma <minux@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/os_solaris.go

@@ -31,71 +31,71 @@ var asmsysvicall6 libcFunc
 
 //go:nosplit
 func sysvicall0(fn *libcFunc) uintptr {
-	libcall := &getg().m.libcall
+	var libcall libcall
 	libcall.fn = uintptr(unsafe.Pointer(fn))
 	libcall.n = 0
 	libcall.args = uintptr(unsafe.Pointer(fn)) // it's unused but must be non-nil, otherwise crashes
-	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(libcall))
+	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&libcall))
 	return libcall.r1
 }
 
 //go:nosplit
 func sysvicall1(fn *libcFunc, a1 uintptr) uintptr {
-	libcall := &getg().m.libcall
+	var libcall libcall
 	libcall.fn = uintptr(unsafe.Pointer(fn))
 	libcall.n = 1
 	// TODO(rsc): Why is noescape necessary here and below?
 	libcall.args = uintptr(noescape(unsafe.Pointer(&a1)))
-	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(libcall))
+	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&libcall))
 	return libcall.r1
 }
 
 //go:nosplit
 func sysvicall2(fn *libcFunc, a1, a2 uintptr) uintptr {
-	libcall := &getg().m.libcall
+	var libcall libcall
 	libcall.fn = uintptr(unsafe.Pointer(fn))
 	libcall.n = 2
 	libcall.args = uintptr(noescape(unsafe.Pointer(&a1)))
-	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(libcall))
+	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&libcall))
 	return libcall.r1
 }
 
 //go:nosplit
 func sysvicall3(fn *libcFunc, a1, a2, a3 uintptr) uintptr {
-	libcall := &getg().m.libcall
+	var libcall libcall
 	libcall.fn = uintptr(unsafe.Pointer(fn))
 	libcall.n = 3
 	libcall.args = uintptr(noescape(unsafe.Pointer(&a1)))
-	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(libcall))
+	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&libcall))
 	return libcall.r1
 }
 
 //go:nosplit
 func sysvicall4(fn *libcFunc, a1, a2, a3, a4 uintptr) uintptr {
-	libcall := &getg().m.libcall
+	var libcall libcall
 	libcall.fn = uintptr(unsafe.Pointer(fn))
 	libcall.n = 4
 	libcall.args = uintptr(noescape(unsafe.Pointer(&a1)))
-	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(libcall))
+	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&libcall))
 	return libcall.r1
 }
 
 //go:nosplit
 func sysvicall5(fn *libcFunc, a1, a2, a3, a4, a5 uintptr) uintptr {
-	libcall := &getg().m.libcall
+	var libcall libcall
 	libcall.fn = uintptr(unsafe.Pointer(fn))
 	libcall.n = 5
 	libcall.args = uintptr(noescape(unsafe.Pointer(&a1)))
-	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(libcall))
+	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&libcall))
 	return libcall.r1
 }
 
 //go:nosplit
 func sysvicall6(fn *libcFunc, a1, a2, a3, a4, a5, a6 uintptr) uintptr {
-	libcall := &getg().m.libcall
+	var libcall libcall
 	libcall.fn = uintptr(unsafe.Pointer(fn))
 	libcall.n = 6
 	libcall.args = uintptr(noescape(unsafe.Pointer(&a1)))
-	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(libcall))
+	asmcgocall(unsafe.Pointer(&asmsysvicall6), unsafe.Pointer(&libcall))
 	return libcall.r1
 }

src/runtime/sys_solaris_amd64.s

@@ -80,6 +80,8 @@ TEXT runtime·asmsysvicall6(SB),NOSPLIT,$0
 
 	get_tls(CX)
 	MOVQ	g(CX), BX
+	CMPQ	BX, $0
+	JEQ	skiperrno1
 	MOVQ	g_m(BX), BX
 	MOVQ	(m_mOS+mOS_perrno)(BX), DX
 	CMPQ	DX, $0
@@ -108,6 +110,8 @@ skipargs:
 
 	get_tls(CX)
 	MOVQ	g(CX), BX
+	CMPQ	BX, $0
+	JEQ	skiperrno2
 	MOVQ	g_m(BX), BX
 	MOVQ	(m_mOS+mOS_perrno)(BX), AX
 	CMPQ	AX, $0