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 <[email protected]>
Reviewed-by: Emmanuel Odeke <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Go Bot <[email protected]>

Author: AndrewGMorgan

src/syscall/syscall_linux.go

@@ -1003,7 +1003,9 @@ func (pc *allThreadsCaller) doSyscall(initial bool) bool {
 		pc.r1 = r1
 		pc.r2 = r2
 		pc.err = err
-	} else if pc.r1 != r1 || pc.r2 != r2 || pc.err != err {
+	} else if pc.r1 != r1 || (archHonorsR2 && pc.r2 != r2) || pc.err != err {
+		print("trap:", pc.trap, ", a123=[", pc.a1, ",", pc.a2, ",", pc.a3, "]\n")
+		print("results: got {r1=", r1, ",r2=", r2, ",err=", err, "}, want {r1=", pc.r1, ",r2=", pc.r2, ",r3=", pc.err, "}\n")
 		panic("AllThreadsSyscall results differ between threads; runtime corrupted")
 	}
 	return err == 0
@@ -1019,7 +1021,9 @@ func (pc *allThreadsCaller) doSyscall6(initial bool) bool {
 		pc.r1 = r1
 		pc.r2 = r2
 		pc.err = err
-	} else if pc.r1 != r1 || pc.r2 != r2 || pc.err != err {
+	} else if pc.r1 != r1 || (archHonorsR2 && pc.r2 != r2) || pc.err != err {
+		print("trap:", pc.trap, ", a123456=[", pc.a1, ",", pc.a2, ",", pc.a3, ",", pc.a4, ",", pc.a5, ",", pc.a6, "]\n")
+		print("results: got {r1=", r1, ",r2=", r2, ",err=", err, "}, want {r1=", pc.r1, ",r2=", pc.r2, ",r3=", pc.err, "}\n")
 		panic("AllThreadsSyscall6 results differ between threads; runtime corrupted")
 	}
 	return err == 0

src/syscall/syscall_linux_386.go

@@ -6,6 +6,12 @@ package syscall
 
 import "unsafe"
 
+// archHonorsR2 captures the fact that r2 is honored by the
+// runtime.GOARCH.  Syscall conventions are generally r1, r2, err :=
+// syscall(trap, ...).  Not all architectures define r2 in their
+// ABI. See "man syscall".
+const archHonorsR2 = true
+
 const _SYS_setgroups = SYS_SETGROUPS32
 
 func setTimespec(sec, nsec int64) Timespec {

src/syscall/syscall_linux_amd64.go

@@ -4,6 +4,12 @@
 
 package syscall
 
+// archHonorsR2 captures the fact that r2 is honored by the
+// runtime.GOARCH.  Syscall conventions are generally r1, r2, err :=
+// syscall(trap, ...).  Not all architectures define r2 in their
+// ABI. See "man syscall".
+const archHonorsR2 = true
+
 const _SYS_setgroups = SYS_SETGROUPS
 
 //sys	Dup2(oldfd int, newfd int) (err error)

src/syscall/syscall_linux_arm.go

@@ -6,6 +6,12 @@ package syscall
 
 import "unsafe"
 
+// archHonorsR2 captures the fact that r2 is honored by the
+// runtime.GOARCH.  Syscall conventions are generally r1, r2, err :=
+// syscall(trap, ...).  Not all architectures define r2 in their
+// ABI. See "man syscall". [EABI assumed.]
+const archHonorsR2 = true
+
 const _SYS_setgroups = SYS_SETGROUPS32
 
 func setTimespec(sec, nsec int64) Timespec {

src/syscall/syscall_linux_arm64.go

@@ -6,6 +6,12 @@ package syscall
 
 import "unsafe"
 
+// archHonorsR2 captures the fact that r2 is honored by the
+// runtime.GOARCH.  Syscall conventions are generally r1, r2, err :=
+// syscall(trap, ...).  Not all architectures define r2 in their
+// ABI. See "man syscall".
+const archHonorsR2 = true
+
 const _SYS_setgroups = SYS_SETGROUPS
 
 func EpollCreate(size int) (fd int, err error) {

src/syscall/syscall_linux_mips64x.go

@@ -7,6 +7,12 @@
 
 package syscall
 
+// archHonorsR2 captures the fact that r2 is honored by the
+// runtime.GOARCH.  Syscall conventions are generally r1, r2, err :=
+// syscall(trap, ...).  Not all architectures define r2 in their
+// ABI. See "man syscall".
+const archHonorsR2 = true
+
 const _SYS_setgroups = SYS_SETGROUPS
 
 //sys	Dup2(oldfd int, newfd int) (err error)

src/syscall/syscall_linux_mipsx.go

@@ -9,6 +9,12 @@ package syscall
 
 import "unsafe"
 
+// archHonorsR2 captures the fact that r2 is honored by the
+// runtime.GOARCH.  Syscall conventions are generally r1, r2, err :=
+// syscall(trap, ...).  Not all architectures define r2 in their
+// ABI. See "man syscall".
+const archHonorsR2 = true
+
 const _SYS_setgroups = SYS_SETGROUPS
 
 func Syscall9(trap, a1, a2, a3, a4, a5, a6, a7, a8, a9 uintptr) (r1, r2 uintptr, err Errno)

src/syscall/syscall_linux_ppc64x.go

@@ -7,6 +7,12 @@
 
 package syscall
 
+// archHonorsR2 captures the fact that r2 is honored by the
+// runtime.GOARCH.  Syscall conventions are generally r1, r2, err :=
+// syscall(trap, ...).  Not all architectures define r2 in their
+// ABI. See "man syscall".
+const archHonorsR2 = false
+
 const _SYS_setgroups = SYS_SETGROUPS
 
 //sys	Dup2(oldfd int, newfd int) (err error)

src/syscall/syscall_linux_riscv64.go

@@ -6,6 +6,12 @@ package syscall
 
 import "unsafe"
 
+// archHonorsR2 captures the fact that r2 is honored by the
+// runtime.GOARCH.  Syscall conventions are generally r1, r2, err :=
+// syscall(trap, ...).  Not all architectures define r2 in their
+// ABI. See "man syscall".
+const archHonorsR2 = true
+
 const _SYS_setgroups = SYS_SETGROUPS
 
 func EpollCreate(size int) (fd int, err error) {

src/syscall/syscall_linux_s390x.go

@@ -6,6 +6,12 @@ package syscall
 
 import "unsafe"
 
+// archHonorsR2 captures the fact that r2 is honored by the
+// runtime.GOARCH.  Syscall conventions are generally r1, r2, err :=
+// syscall(trap, ...).  Not all architectures define r2 in their
+// ABI. See "man syscall".
+const archHonorsR2 = true
+
 const _SYS_setgroups = SYS_SETGROUPS
 
 //sys	Dup2(oldfd int, newfd int) (err error)

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 {