cmd/go, misc: rework cwd handling for iOS tests

Another change in behvaior (bug) in LLDB. Despite the fact that
LLDB can dump the symtab of our test binaries and show the function
addresses, it can no longer call the functions. This means the chdir
trick on signal is failing.

This CL uses a new trick. For iOS, the exec script passes the change
in directory as an argument, and it is processed early by the test
harness generated by cmd/go.

For the iOS builders.

Change-Id: I8f5d0f831fe18de99f097761f89c5184d5bf2afb
Reviewed-on: https://go-review.googlesource.com/35152Reviewed-by: Elias Naur <elias.naur@gmail.com>
Run-TryBot: David Crawshaw <crawshaw@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/ios/go_darwin_arm_exec.go

@@ -204,6 +204,11 @@ func run(bin string, args []string) (err error) {
 	var opts options
 	opts, args = parseArgs(args)
 
+	// Pass the suffix for the current working directory as the
+	// first argument to the test. For iOS, cmd/go generates
+	// special handling of this argument.
+	args = append([]string{"cwdSuffix=" + pkgpath}, args...)
+
 	// ios-deploy invokes lldb to give us a shell session with the app.
 	s, err := newSession(appdir, args, opts)
 	if err != nil {
@@ -241,15 +246,6 @@ func run(bin string, args []string) (err error) {
 
 	s.doCmd("run", "stop reason = signal SIGUSR2", 20*time.Second)
 
-	// Move the current working directory into the faux gopath.
-	if pkgpath != "src" {
-		s.do(`breakpoint delete 1`)
-		s.do(`expr char* $mem = (char*)malloc(512)`)
-		s.do(`expr $mem = (char*)getwd($mem, 512)`)
-		s.do(`expr $mem = (char*)strcat($mem, "/` + pkgpath + `")`)
-		s.do(`call (void)chdir($mem)`)
-	}
-
 	startTestsLen := s.out.Len()
 	fmt.Fprintln(s.in, `process continue`)
 

src/cmd/go/test.go

@@ -1532,12 +1532,28 @@ func coverRegisterFile(fileName string, counter []uint32, pos []uint32, numStmts
 func main() {
 {{if .IsIOS}}
 	// Send a SIGUSR2, which will be intercepted by LLDB to
-	// tell the test harness that installation was successful,
-	// and to give the exec script a chance set the current
-	// working directory. See misc/ios/go_darwin_arm_exec.go.
+	// tell the test harness that installation was successful.
+	// See misc/ios/go_darwin_arm_exec.go.
 	signal.Notify(make(chan os.Signal), syscall.SIGUSR2)
 	syscall.Kill(0, syscall.SIGUSR2)
 	signal.Reset(syscall.SIGUSR2)
+
+	// The first argument supplied to an iOS test is an offset
+	// suffix for the current working directory.
+	// Process it here, and remove it from os.Args.
+	const hdr = "cwdSuffix="
+	if len(os.Args) < 2 || len(os.Args[1]) <= len(hdr) || os.Args[1][:len(hdr)] != hdr {
+		panic("iOS test not passed a working directory suffix")
+	}
+	suffix := os.Args[1][len(hdr):]
+	dir, err := os.Getwd()
+	if err != nil {
+		panic(err)
+	}
+	if err := os.Chdir(dir + "/" + suffix); err != nil {
+		panic(err)
+	}
+	os.Args = append([]string{os.Args[0]}, os.Args[2:]...)
 {{end}}
 
 {{if .CoverEnabled}}