On FreeBSD the extern char** environ symbol is defined in the CRT rather than libc. This is known to cause linking problems for shared libraries when the linker is passed --no-undefined. The usual workaround for this issue is to resolve environ dynamically as suggested in https://reviews.freebsd.org/D30842#840642 I already pushed such a fix into LLVM and some other projects.

I've put up a minimal reproduction code at https://github.com/arrowd/rust-environ-problem Simply run make to get the linking error.

CC @asomers