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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package debug contains facilities for programs to debug themselves while
// they are running.
package debug
import (
"internal/poll"
"os"
"runtime"
_ "unsafe" // for linkname
)
// PrintStack prints to standard error the stack trace returned by runtime.Stack.
func PrintStack() {
os.Stderr.Write(Stack())
}
// Stack returns a formatted stack trace of the goroutine that calls it.
// It calls [runtime.Stack] with a large enough buffer to capture the entire trace.
func Stack() []byte {
buf := make([]byte, 1024)
for {
n := runtime.Stack(buf, false)
if n < len(buf) {
return buf[:n]
}
buf = make([]byte, 2*len(buf))
}
}
// CrashOptions provides options that control the formatting of the
// fatal crash message.
type CrashOptions struct {
/* for future expansion */
}
// 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.
// SetCrashOutput duplicates f's file descriptor, so the caller may safely
// close f as soon as SetCrashOutput returns.
// To disable this additional crash output, call SetCrashOutput(nil).
// If called concurrently with a crash, some in-progress output may be written
// to the old file even after an overriding SetCrashOutput returns.
func SetCrashOutput(f *os.File, opts CrashOptions) 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