9.21.4 Assembler Directives
The 68HC11 and 68HC12 version of as have the following
specific assembler directives:
     
.relax- The relax directive is used by the GNU Compiler to emit a specific
relocation to mark a group of instructions for linker relaxation. 
The sequence of instructions within the group must be known to the linker
so that relaxation can be performed.
     
 .mode [mshort|mlong|mshort-double|mlong-double]- This directive specifies the ABI.  It overrides the -mshort,
-mlong, -mshort-double and -mlong-double options.
     
 .far symbol- This directive marks the symbol as a far symbol meaning that it
uses a call/rtc calling convention as opposed to jsr/rts. 
During a final link, the linker will identify references to the far
symbol and will verify the proper calling convention.
     
 .interrupt symbol- This directive marks the symbol as an interrupt entry point. 
This information is then used by the debugger to correctly unwind the
frame across interrupts.
     
 .xrefb symbol- This directive is defined for compatibility with the
Specification for Motorola 8 and 16-Bit Assembly Language Input
Standard and is ignored.