Clemson University -- CPSC 231 -- Fall 2009


ABI - application binary interface

  - a specification defining requirements for portability of applications
      at binary level (i.e., executables)
  - no recompilation or relinking 
  - interoperability (assembly language subroutine can be called from HLL)

  - usually associated with a particular OS or OS family
  - thus, an executable compiled according to one ABI will not
      typically run under a different OS on the same machine

  - also: allows assembly language routines to be called from HLL routines,
      and HLL routines to be called from assembly language routines


specifications in ABI include:

  - specific processor or processor family
  - any required processor features (e.g., SIMD instructions)
  - data formats
  - register usage conventions
  - stack frame format
  - parameter passing, including fp/structure/union parameters
  - return value passing, including fp/structure/union return values
  - specific OS or OS family
  - object and executable file formats

example register conventions

  - actual parameters
  - return value(s)
  - return address
  - stack pointer
  - frame pointer
  - global area pointer
  - constant pool pointer
  - temporaries
  - caller-saved (if caller wants them preserved over call, caller must
      save and retore)
  - callee-saved (if called subroutines wants to use them, subroutine
      must save and retore)


SPARC SYSV ABI - http://www.sparc.com/standards/psABI3rd.pdf

  SPARC register usage conventions

    %i0-%i5 -- incoming parameters
    %i6     -- frame pointer
    %i7     -- address of call instruction (return to %i7 + 8 if save)

    %l0-%l7 -- all yours

    %o0     -- all yours, but also used to pass a parameter to and/or return a
               value from a subroutine
    %o1-%o5 -- all yours, but also used to pass parameters to a subroutine
    %o6     -- stack pointer
    %o7     -- address of call instruction (return to %o7 + 8 if no save)

    %g0     -- always zero
    %g1     -- all yours, volatile across calls
    %g2-%g4 -- "reserved to application"
    %g5-%g7 -- "reserved to the system"

  stack frame must be doubleword-aligned


for comparison - MIPS register conventions (cf. p. 376)

  register  alt. name  - usage
  --------  ---------    -----

  r0        $zero      - constant 0 (designed into the hardware)
  r1        $at        - reserved for assembler
  r2-r3     $v0-$v1    - expression evaluation and function return value
  r4-r7     $a0-$a3    - four arguments
  r8-r15    $t0-$t7    - eight temporaries (not preserved across calls)
  r16-r23   $s0-$s7    - eight saved temporaries (preserved across calls)
  r24-r25   $t8-$t9    - two temporaries (not preserved across calls)
  r26-r27   $k0-$k1    - reserved for OS kernel
  r28       $gp        - pointer to global area
  r29       $sp        - stack pointer
  r30       $fp        - frame pointer
  r31       $ra        - return address (usage designed into the hardware)


have to save registers in absence of full info about caller and subroutine

  caller-save registers

    save in caller before call, restore after return
    opt.: save only those registers that have to be preserved across call

  callee-save registers

    save in subroutine prolog, restore in epilog
    opt.: save only those registers that are actually used in subroutine

  possible optimization: link-time register allocation (for static linking)