diff options
Diffstat (limited to 'src/runtime/debug/stack.go')
| -rw-r--r-- | src/runtime/debug/stack.go | 53 |
1 files changed, 53 insertions, 0 deletions
diff --git a/src/runtime/debug/stack.go b/src/runtime/debug/stack.go index 3999840d3c..508afe1f97 100644 --- a/src/runtime/debug/stack.go +++ b/src/runtime/debug/stack.go @@ -7,8 +7,10 @@ package debug import ( + "internal/poll" "os" "runtime" + _ "unsafe" // for linkname ) // PrintStack prints to standard error the stack trace returned by runtime.Stack. @@ -28,3 +30,54 @@ func Stack() []byte { buf = make([]byte, 2*len(buf)) } } + +// SetCrashOutput configures a single additional file where unhandled +// panics and other fatal errors are printed, in addition to standard error. +// There is only one additional file: calling SetCrashOutput again +// overrides any earlier call; it does not close the previous file. +// SetCrashOutput(nil) disables the use of any additional file. +func SetCrashOutput(f *os.File) error { + fd := ^uintptr(0) + if f != nil { + // The runtime will write to this file descriptor from + // low-level routines during a panic, possibly without + // a G, so we must call f.Fd() eagerly. This creates a + // danger that that the file descriptor is no longer + // valid at the time of the write, because the caller + // (incorrectly) called f.Close() and the kernel + // reissued the fd in a later call to open(2), leading + // to crashes being written to the wrong file. + // + // So, we duplicate the fd to obtain a private one + // that cannot be closed by the user. + // This also alleviates us from concerns about the + // lifetime and finalization of f. + // (DupCloseOnExec returns an fd, not a *File, so + // there is no finalizer, and we are responsible for + // closing it.) + // + // The new fd must be close-on-exec, otherwise if the + // crash monitor is a child process, it may inherit + // it, so it will never see EOF from the pipe even + // when this process crashes. + // + // A side effect of Fd() is that it calls SetBlocking, + // which is important so that writes of a crash report + // to a full pipe buffer don't get lost. + fd2, _, err := poll.DupCloseOnExec(int(f.Fd())) + if err != nil { + return err + } + runtime.KeepAlive(f) // prevent finalization before dup + fd = uintptr(fd2) + } + if prev := runtime_setCrashFD(fd); prev != ^uintptr(0) { + // We use NewFile+Close because it is portable + // unlike syscall.Close, whose parameter type varies. + os.NewFile(prev, "").Close() // ignore error + } + return nil +} + +//go:linkname runtime_setCrashFD runtime.setCrashFD +func runtime_setCrashFD(uintptr) uintptr |