firefox segfaults after zlib upgrade

After some emerging, my firefox suddenly started segfaulting everytime. The worst part of a segfault is you don’t get anything useful out of it, no error message, etc. A backtrace in gdb shows the problem is from a recent upgrade of sys-libs/zlib, and google says it’s an old problem, and as usual, gentoo devs refuse to fix it (maybe for a good reason, but who cares).

Some more googling brought me to this gcc ML post. The solution is simply to add -mstackrealign into your /etc/make.conf. Re-emerge zlib then solves the problem.