os: check return value as well as error from waitid
https://gcc.gnu.org/PR86331 indicates that if a signal handler runs it
is possible for syscall.Syscall6 to return a non-zero errno value even
if no error occurs. That is a problem in general, but this fix will
let us work around the general problem for the specific case of
calling waitid.
Change-Id: I3d9db9ea16b0256eba7f88962909f287db3a7955
Reviewed-on: https://go-review.googlesource.com/121595
Reviewed-by: Than McIntosh <thanm@google.com>
diff --git a/libgo/go/os/wait_waitid.go b/libgo/go/os/wait_waitid.go
index 5a62b27..a6284aa 100644
--- a/libgo/go/os/wait_waitid.go
+++ b/libgo/go/os/wait_waitid.go
@@ -28,9 +28,12 @@
// We don't care about the values it returns.
var siginfo [16]uint64
psig := &siginfo[0]
- _, _, e := syscall.Syscall6(syscall.SYS_WAITID, _P_PID, uintptr(p.Pid), uintptr(unsafe.Pointer(psig)), syscall.WEXITED|syscall.WNOWAIT, 0, 0)
+ r, _, e := syscall.Syscall6(syscall.SYS_WAITID, _P_PID, uintptr(p.Pid), uintptr(unsafe.Pointer(psig)), syscall.WEXITED|syscall.WNOWAIT, 0, 0)
runtime.KeepAlive(p)
- if e != 0 {
+ // Check r as well as e because syscall.Syscall6 currently
+ // just returns errno, and the SIGCHLD signal handler may
+ // change errno. See https://gcc.gnu.org/PR86331.
+ if r != 0 && e != 0 {
// waitid has been available since Linux 2.6.9, but
// reportedly is not available in Ubuntu on Windows.
// See issue 16610.
