Caddy: Panic when using FastCGI on certain architectures

Created on 22 Dec 2016 · 9Comments · Source: caddyserver/caddy

Using FastCGI with Caddy 0.9.4 leads to a invalid memory address or nil pointer dereference in go/src/sync/atomic/asm_*.s on: ARMv6, ARMv7, i686. Everything works on: amd64. Always using Linux.

See https://forum.caddyserver.com/t/panic-with-ssl-fcgi/1168/10?u=22749

$ cd /tmp
$ wget https://www.saddi.com/software/flup/dist/flup-1.0.2.tar.gz
$ tar -xzvf flup-1.0.2.tar.gz
$ cd flup-1.0.2
$ cat > hello.py
def myapp(environ, start_response):
    start_response('200 OK', [('Content-Type', 'text/plain')])
    return ['Hello World!\n']

if __name__ == '__main__':
    from flup.server.fcgi import WSGIServer
    WSGIServer(myapp, bindAddress='fcgi.sock').run()


$ cat > Caddyfile
:2016
fastcgi / /tmp/flup-1.0.2/fcgi.sock
$ caddy -log stderr &
$ curl http://localhost:2016
2016/12/22 22:32:34 [PANIC] runtime error: invalid memory address or nil pointer dereference
500 Internal Server Error

Without the fastcgi directive there is no panic. All architectures worked fine with Caddy 0.9.3. All builds came from https://caddyserver.com/download

bug

Source

tewe

Most helpful comment

Works for me on Raspberry Pi 1 (ARMv6)

BTW cross-compiling was amazingly simple

tewe on 22 Dec 2016

🎉2

All 9 comments

Aha - while I'm only speculating, I bet this is it (see third bug, about word alignment): https://golang.org/pkg/sync/atomic/#pkg-note-BUG

See https://sourcegraph.com/github.com/mholt/caddy@c972ea39c8b40c28506958bb43d31d2ed357e9f2/-/blob/caddyhttp/fastcgi/dialer.go#L71-72 - I'm guessing this field is not aligned properly. @wendigo - when you have a chance, could you swap that up to the first field in the struct instead of the second? And then see if there are any other fields like that which need to be re-aligned.