syscall: handle undefined r2 value on linux-ppc64x

This change fixes two failng tests on linux-ppc64x:

- TestAllThreadsSyscall() exposed a real bug in the ppc64x support:
  - It turns out that the r2 syscall return value is not defined
    on all architectures. Notably linux-ppc64x so address that by
    introducing a private architectural constant in the syscall
    package, archHonorsR2: true if r2 has a determanistic value.

- TestSetuidEtc() was sensitive to /proc/<PID>/status content:
  - The amount of padding space has changed with kernel vintage.
  - Stress testing revealed a race with /proc files disappearing.

Fixes #42178

Change-Id: Ie6fc0b8f2f94a409ac0e5756e73bfce113274709
Reviewed-on: https://go-review.googlesource.com/c/go/+/266202
Run-TryBot: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>

1 files changed, 31 insertions, 29 deletions

diff --git a/src/syscall/syscall_linux_test.go b/src/syscall/syscall_linux_test.go
index 0742ef5b07..41ae8cc5a1 100644
--- a/src/syscall/syscall_linux_test.go
+++ b/src/syscall/syscall_linux_test.go
@@ -410,9 +410,6 @@ const (
 // syscalls that execute on all OSThreads - with which to support
 // POSIX semantics for security state changes.
 func TestAllThreadsSyscall(t *testing.T) {
-	if runtime.GOARCH == "ppc64" {
-		t.Skip("skipping on linux/ppc64; see issue #42178")
-	}
 	if _, _, err := syscall.AllThreadsSyscall(syscall.SYS_PRCTL, PR_SET_KEEPCAPS, 0, 0); err == syscall.ENOTSUP {
 		t.Skip("AllThreadsSyscall disabled with cgo")
 	}
@@ -544,7 +541,7 @@ func TestAllThreadsSyscall(t *testing.T) {
 // compareStatus is used to confirm the contents of the thread
 // specific status files match expectations.
 func compareStatus(filter, expect string) error {
-	expected := filter + "\t" + expect
+	expected := filter + expect
 	pid := syscall.Getpid()
 	fs, err := ioutil.ReadDir(fmt.Sprintf("/proc/%d/task", pid))
 	if err != nil {
@@ -553,14 +550,22 @@ func compareStatus(filter, expect string) error {
 	for _, f := range fs {
 		tf := fmt.Sprintf("/proc/%s/status", f.Name())
 		d, err := ioutil.ReadFile(tf)
+		if os.IsNotExist(err) {
+			// We are racing against threads dying, which
+			// is out of our control, so ignore the
+			// missing file and skip to the next one.
+			continue
+		}
 		if err != nil {
 			return fmt.Errorf("unable to read %q: %v", tf, err)
 		}
 		lines := strings.Split(string(d), "\n")
 		for _, line := range lines {
+			// Different kernel vintages pad differently.
+			line = strings.TrimSpace(line)
 			if strings.HasPrefix(line, filter) {
 				if line != expected {
-					return fmt.Errorf("%s %s (bad)\n", tf, line)
+					return fmt.Errorf("%q got:%q want:%q (bad)\n", tf, line, expected)
 				}
 				break
 			}
@@ -580,9 +585,6 @@ func compareStatus(filter, expect string) error {
 // the syscalls. Care should be taken to mirror any enhancements to
 // this test here in that file too.
 func TestSetuidEtc(t *testing.T) {
-	if runtime.GOARCH == "ppc64" {
-		t.Skip("skipping on linux/ppc64; see issue #42178")
-	}
 	if syscall.Getuid() != 0 {
 		t.Skip("skipping root only test")
 	}
@@ -591,34 +593,34 @@ func TestSetuidEtc(t *testing.T) {
 		fn             func() error
 		filter, expect string
 	}{
-		{call: "Setegid(1)", fn: func() error { return syscall.Setegid(1) }, filter: "Gid:", expect: "0\t1\t0\t1"},
-		{call: "Setegid(0)", fn: func() error { return syscall.Setegid(0) }, filter: "Gid:", expect: "0\t0\t0\t0"},
+		{call: "Setegid(1)", fn: func() error { return syscall.Setegid(1) }, filter: "Gid:", expect: "\t0\t1\t0\t1"},
+		{call: "Setegid(0)", fn: func() error { return syscall.Setegid(0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},
 
-		{call: "Seteuid(1)", fn: func() error { return syscall.Seteuid(1) }, filter: "Uid:", expect: "0\t1\t0\t1"},
-		{call: "Setuid(0)", fn: func() error { return syscall.Setuid(0) }, filter: "Uid:", expect: "0\t0\t0\t0"},
+		{call: "Seteuid(1)", fn: func() error { return syscall.Seteuid(1) }, filter: "Uid:", expect: "\t0\t1\t0\t1"},
+		{call: "Setuid(0)", fn: func() error { return syscall.Setuid(0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},
 
-		{call: "Setgid(1)", fn: func() error { return syscall.Setgid(1) }, filter: "Gid:", expect: "1\t1\t1\t1"},
-		{call: "Setgid(0)", fn: func() error { return syscall.Setgid(0) }, filter: "Gid:", expect: "0\t0\t0\t0"},
+		{call: "Setgid(1)", fn: func() error { return syscall.Setgid(1) }, filter: "Gid:", expect: "\t1\t1\t1\t1"},
+		{call: "Setgid(0)", fn: func() error { return syscall.Setgid(0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},
 
-		{call: "Setgroups([]int{0,1,2,3})", fn: func() error { return syscall.Setgroups([]int{0, 1, 2, 3}) }, filter: "Groups:", expect: "0 1 2 3 "},
-		{call: "Setgroups(nil)", fn: func() error { return syscall.Setgroups(nil) }, filter: "Groups:", expect: " "},
-		{call: "Setgroups([]int{0})", fn: func() error { return syscall.Setgroups([]int{0}) }, filter: "Groups:", expect: "0 "},
+		{call: "Setgroups([]int{0,1,2,3})", fn: func() error { return syscall.Setgroups([]int{0, 1, 2, 3}) }, filter: "Groups:", expect: "\t0 1 2 3"},
+		{call: "Setgroups(nil)", fn: func() error { return syscall.Setgroups(nil) }, filter: "Groups:", expect: ""},
+		{call: "Setgroups([]int{0})", fn: func() error { return syscall.Setgroups([]int{0}) }, filter: "Groups:", expect: "\t0"},
 
-		{call: "Setregid(101,0)", fn: func() error { return syscall.Setregid(101, 0) }, filter: "Gid:", expect: "101\t0\t0\t0"},
-		{call: "Setregid(0,102)", fn: func() error { return syscall.Setregid(0, 102) }, filter: "Gid:", expect: "0\t102\t102\t102"},
-		{call: "Setregid(0,0)", fn: func() error { return syscall.Setregid(0, 0) }, filter: "Gid:", expect: "0\t0\t0\t0"},
+		{call: "Setregid(101,0)", fn: func() error { return syscall.Setregid(101, 0) }, filter: "Gid:", expect: "\t101\t0\t0\t0"},
+		{call: "Setregid(0,102)", fn: func() error { return syscall.Setregid(0, 102) }, filter: "Gid:", expect: "\t0\t102\t102\t102"},
+		{call: "Setregid(0,0)", fn: func() error { return syscall.Setregid(0, 0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},
 
-		{call: "Setreuid(1,0)", fn: func() error { return syscall.Setreuid(1, 0) }, filter: "Uid:", expect: "1\t0\t0\t0"},
-		{call: "Setreuid(0,2)", fn: func() error { return syscall.Setreuid(0, 2) }, filter: "Uid:", expect: "0\t2\t2\t2"},
-		{call: "Setreuid(0,0)", fn: func() error { return syscall.Setreuid(0, 0) }, filter: "Uid:", expect: "0\t0\t0\t0"},
+		{call: "Setreuid(1,0)", fn: func() error { return syscall.Setreuid(1, 0) }, filter: "Uid:", expect: "\t1\t0\t0\t0"},
+		{call: "Setreuid(0,2)", fn: func() error { return syscall.Setreuid(0, 2) }, filter: "Uid:", expect: "\t0\t2\t2\t2"},
+		{call: "Setreuid(0,0)", fn: func() error { return syscall.Setreuid(0, 0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},
 
-		{call: "Setresgid(101,0,102)", fn: func() error { return syscall.Setresgid(101, 0, 102) }, filter: "Gid:", expect: "101\t0\t102\t0"},
-		{call: "Setresgid(0,102,101)", fn: func() error { return syscall.Setresgid(0, 102, 101) }, filter: "Gid:", expect: "0\t102\t101\t102"},
-		{call: "Setresgid(0,0,0)", fn: func() error { return syscall.Setresgid(0, 0, 0) }, filter: "Gid:", expect: "0\t0\t0\t0"},
+		{call: "Setresgid(101,0,102)", fn: func() error { return syscall.Setresgid(101, 0, 102) }, filter: "Gid:", expect: "\t101\t0\t102\t0"},
+		{call: "Setresgid(0,102,101)", fn: func() error { return syscall.Setresgid(0, 102, 101) }, filter: "Gid:", expect: "\t0\t102\t101\t102"},
+		{call: "Setresgid(0,0,0)", fn: func() error { return syscall.Setresgid(0, 0, 0) }, filter: "Gid:", expect: "\t0\t0\t0\t0"},
 
-		{call: "Setresuid(1,0,2)", fn: func() error { return syscall.Setresuid(1, 0, 2) }, filter: "Uid:", expect: "1\t0\t2\t0"},
-		{call: "Setresuid(0,2,1)", fn: func() error { return syscall.Setresuid(0, 2, 1) }, filter: "Uid:", expect: "0\t2\t1\t2"},
-		{call: "Setresuid(0,0,0)", fn: func() error { return syscall.Setresuid(0, 0, 0) }, filter: "Uid:", expect: "0\t0\t0\t0"},
+		{call: "Setresuid(1,0,2)", fn: func() error { return syscall.Setresuid(1, 0, 2) }, filter: "Uid:", expect: "\t1\t0\t2\t0"},
+		{call: "Setresuid(0,2,1)", fn: func() error { return syscall.Setresuid(0, 2, 1) }, filter: "Uid:", expect: "\t0\t2\t1\t2"},
+		{call: "Setresuid(0,0,0)", fn: func() error { return syscall.Setresuid(0, 0, 0) }, filter: "Uid:", expect: "\t0\t0\t0\t0"},
 	}
 
 	for i, v := range vs {