cmd/asm: fix assembling return jump

In RET instruction, the operand is the return jump's target,
which should be put in Prog.To.

Add an action "buildrundir" to the test driver, which builds
(compile+assemble+link) the code in a directory and runs the
resulting binary.

Fixes #23838.

Change-Id: I7ebe7eda49024b40a69a24857322c5ca9c67babb
Reviewed-on: https://go-review.googlesource.com/94175
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>

2 files changed, 44 insertions, 0 deletions

diff --git a/test/retjmp.dir/a.s b/test/retjmp.dir/a.s
new file mode 100644
index 0000000000..c67a06638f
--- /dev/null
+++ b/test/retjmp.dir/a.s
@@ -0,0 +1,12 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+TEXT	·f(SB), 4, $8-0
+	CALL	·f1(SB)
+	RET	·f2(SB)
+	CALL	·unreachable(SB)
+
+TEXT	·leaf(SB), 4, $0-0
+	RET	·f3(SB)
+	JMP	·unreachable(SB)
diff --git a/test/retjmp.dir/main.go b/test/retjmp.dir/main.go
new file mode 100644
index 0000000000..cb4bd018bf
--- /dev/null
+++ b/test/retjmp.dir/main.go
@@ -0,0 +1,32 @@
+// Copyright 2018 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+func f()
+func leaf()
+
+var f1called, f2called, f3called bool
+
+func main() {
+	f()
+	if !f1called {
+		panic("f1 not called")
+	}
+	if !f2called {
+		panic("f2 not called")
+	}
+	leaf()
+	if !f3called {
+		panic("f3 not called")
+	}
+}
+
+func f1() { f1called = true }
+func f2() { f2called = true }
+func f3() { f3called = true }
+
+func unreachable() {
+	panic("unreachable function called")
+}