Choose the method used to find the roots in the GC. This only applies to our framework GCs. You have a choice of two alternatives: - ``--gcrootfinder=shadowstack``: use a so-called "shadow stack", which is an explicitly maintained custom stack of root pointers. This is the most portable solution. - ``--gcrootfinder=asmgcc``: use assembler hackery to find the roots directly from the normal stack. This is a bit faster, but platform specific. It works so far with GCC or MSVC, on i386 and x86-64. You may have to force the use of the shadowstack root finder if you are running into troubles or if you insist on translating PyPy with other compilers like clang.