running make in the background hangs

I want to be able to build software in the background (usually also under nohup). I find that when I build rocket-chip in the background that the build hangs. As soon as I foreground it, it resumes.

I would like to suggest that this is a bug in your makefile. It is certainly causing me difficulties.

I find it hard to imagine how to make this happen even if I tried to write a makefile to behave this way, so I am wondering how to debug it.

$ cat /etc/os-release
NAME="Ubuntu"
VERSION="14.04.5 LTS, Trusty Tahr"
ID=ubuntu
ID_LIKE=debian
PRETTY_NAME="Ubuntu 14.04.5 LTS"
VERSION_ID="14.04"

$ make --version
GNU Make 4.2
Built for x86_64-pc-linux-gnu

Start by reproducing the hang using the repository's make entry point under background execution and nohup, comparing it with foreground behavior on the reported Ubuntu and GNU Make versions. Trace where the build stops and document the relevant makefile path; done means the same build completes without foregrounding it.

Written by the indexing model from the issue text.