The iOS/ARM toolchain does not know about the following Assembler directives:

• .fnend: marks the end of a function with an unwind table entry.
• .fnstart: marks the start of a function with an unwind table entry.
• .hidden: hides the symbol from other components.
• .movsp: tells the unwinder that reg contains an offset from the current stack pointer. (see compnerd/llvm@8da1908)
• .save: generates unwinder annotations to restore the registers.
• .setfp: makes all unwinder annotations relative to a frame pointer.
• .type: records the given type as the type attribute of a symbol table entry.

See https://sourceware.org/binutils/docs/as/ARM-Directives.html and http://www.informatik.uni-hamburg.de/RZ/software/gnu/gcc/as_7.html

Some directives are not implemented upstream yet: http://llvm.org/bugs/show_bug.cgi?id=18199