Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

cmd/link, runtime: additab can be called twice for the same itab, leading to hangs #17594

mwhudson opened this issue Oct 26, 2016 · 3 comments


Copy link

@mwhudson mwhudson commented Oct 26, 2016

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

tip, and 1.7 (but not 1.6)

What operating system and processor architecture are you using (go env)?

linux/amd64, Ubuntu 16.04

What did you do?

(master)mwhudson@aeglos:/opt/opensource/go/src$ go install -v -buildmode=shared std
(master)mwhudson@aeglos:/opt/opensource/go/src$ cat /opt/opensource/go-test-cases/itabfun.go
package main

import (

func main() {

    fd, err := syscall.Open("/dev/null", os.O_WRONLY, 0644)
    if err == nil {
(master)mwhudson@aeglos:/opt/opensource/go/src$ go run -linkshared /opt/opensource/go-test-cases/newrand.go

What did you expect to see?

The program complete quickly.

What did you see instead?

It hangs.

What is going on here is that the itab for the conversion of _reflect.rtype to reflect.Type, go.itab._reflect.rtype,reflect.Type , ends up in the itablinks of the moduledata for both and the executable. As go.itab.*reflect.rtype,reflect.Type is a global symbol, the dynamic linker puts a pointer to the data in the executable into both itablinks. This means that additab gets called twice for the very same itab, which means that it ends up with its .link member pointing at itself. Anything that then traverses the itab linked list (like WriteHeapDump, but also just unlucky calls to getitab) ends up looping forever.

Copy link
Contributor Author

@mwhudson mwhudson commented Oct 26, 2016

A simple fix is to make the go.itab.* symbols local. This will mean you'll get functionally identical itabs floating around, but not actually identical ones, which I think is safe. We'll see what the trybots think in a moment anyway.

Also paging @crawshaw

Copy link

@crawshaw crawshaw commented Oct 26, 2016

That does sound like an easy fix that should work.

@crawshaw crawshaw added this to the Go1.8 milestone Oct 26, 2016
Copy link

@gopherbot gopherbot commented Oct 26, 2016

CL mentions this issue.

@gopherbot gopherbot closed this in 8b07ec2 Oct 27, 2016
@golang golang locked and limited conversation to collaborators Oct 27, 2017
Sign up for free to subscribe to this conversation on GitHub. Already have an account? Sign in.
None yet
Linked pull requests

Successfully merging a pull request may close this issue.

None yet
3 participants