Macro save_context 

macro_rules! save_context {
    () => { ... };
}

This macro expands to code for restoring context on exit from an exception handler. It saves FPU state, assuming 16 DP registers (a ‘D16’ or ‘D16SP’ FPU configuration). Note that SP-only FPUs still have DP registers

• each DP register holds two SP values.

EABI specifies R4 - R11 and D8-D15 as callee-save, and so we don’t preserve them because any C function we call to handle the exception will preserve/restore them itself as required.

It should match restore_context!.