MALLOC_PERTURB_ is a useful thing. If you are developing on glibc-based systems, I encourage you to put this snippet in your ~/.bash_profile:
MALLOC_PERTURB_=$(($RANDOM % 255 + 1))
I have been using it for the last six years on all my computers (3 laptops running every Fedora x86_64 build released since then), and while things haven’t exploded, it has helped uncover the odd bug every once in a while. One such occasion presented itself this week.
I was busy following Ondrej’s hint, debugging why Eye of GNOME was taking so long to open a file from ownCloud. Imagine my shock when it would just crash after showing the window. The same optimization was working just fine on the gnome-3-18 branch, while master was crashing even without any changes. How could that happen? Obviously, while it was failing for me, it was working fine for all those who run unstable GNOME versions via jhbuild, gnome-continous, Fedora rawhide, etc.. Otherwise we would have been debugging this crash, and not a performance issue.
I guess, most of them didn’t have MALLOC_PERTURB_.
Here is another such story.
In case you were wondering, there is already an update on its way to Fedora 24 address the crash.