The code generated by clang for sppp_auth_send() is incorrect. Because the variadic part handling in sppp_auth_send() consumes arguments in pairs, clang uses two registers to point to the pair, v1 pointing to the first argument (the size) and v0 to the second argument (the pointer).
For some reason, clang assumes the stack is aligned on a 16 byte boundary, as for the first iteration v0 is computed as (v1 or 8), while further iterations use (v1 plus 8). But as seen in your trace, the stack pointer is only aligned on a 8 byte boundary, which causes a completely wrong pointer to be passed to bcopy(). You might want to compile your kernel with CC=gcc for the time being, until this code generation issue gets fixed.
