mirror of
https://gitlab.rtems.org/rtems/rtos/rtems.git
synced 2025-12-06 15:43:15 +00:00
891d63bddd
* bsp.t, BSP_TIMES, callconv.t, ChangeLog, cpumodel.t, cputable.t, fatalerr.t, intr_NOTIMES.t, Makefile.am, memmodel.t, mips.texi, preface.texi, stamp-vti, timeBSP.t, version.texi: New files.
93 lines
3.1 KiB
Perl
93 lines
3.1 KiB
Perl
@c
|
|
@c COPYRIGHT (c) 1988-2002.
|
|
@c On-Line Applications Research Corporation (OAR).
|
|
@c All rights reserved.
|
|
@c
|
|
@c $Id$
|
|
@c
|
|
|
|
@chapter Calling Conventions
|
|
|
|
@section Introduction
|
|
|
|
Each high-level language compiler generates
|
|
subroutine entry and exit code based upon a set of rules known
|
|
as the compiler's calling convention. These rules address the
|
|
following issues:
|
|
|
|
@itemize @bullet
|
|
@item register preservation and usage
|
|
@item parameter passing
|
|
@item call and return mechanism
|
|
@end itemize
|
|
|
|
A compiler's calling convention is of importance when
|
|
interfacing to subroutines written in another language either
|
|
assembly or high-level. Even when the high-level language and
|
|
target processor are the same, different compilers may use
|
|
different calling conventions. As a result, calling conventions
|
|
are both processor and compiler dependent.
|
|
|
|
@section Processor Background
|
|
|
|
The MC68xxx architecture supports a simple yet
|
|
effective call and return mechanism. A subroutine is invoked
|
|
via the branch to subroutine (@code{XXX}) or the jump to subroutine
|
|
(@code{XXX}) instructions. These instructions push the return address
|
|
on the current stack. The return from subroutine (@code{XXX})
|
|
instruction pops the return address off the current stack and
|
|
transfers control to that instruction. It is is important to
|
|
note that the XXX call and return mechanism does not
|
|
automatically save or restore any registers. It is the
|
|
responsibility of the high-level language compiler to define the
|
|
register preservation and usage convention.
|
|
|
|
@section Calling Mechanism
|
|
|
|
All RTEMS directives are invoked using either a @code{XXX}
|
|
or @code{XXX} instruction and return to the user application via the
|
|
@code{XXX} instruction.
|
|
|
|
@section Register Usage
|
|
|
|
As discussed above, the @code{XXX} and @code{XXX} instructions do
|
|
not automatically save any registers. RTEMS uses the registers
|
|
@b{D0}, @b{D1}, @b{A0}, and @b{A1} as scratch registers. These registers are
|
|
not preserved by RTEMS directives therefore, the contents of
|
|
these registers should not be assumed upon return from any RTEMS
|
|
directive.
|
|
|
|
@section Parameter Passing
|
|
|
|
RTEMS assumes that arguments are placed on the
|
|
current stack before the directive is invoked via the @code{XXX} or @code{XXX}
|
|
instruction. The first argument is assumed to be closest to the
|
|
return address on the stack. This means that the first argument
|
|
of the C calling sequence is pushed last. The following
|
|
pseudo-code illustrates the typical sequence used to call a
|
|
RTEMS directive with three (3) arguments:
|
|
|
|
@example
|
|
@group
|
|
push third argument
|
|
push second argument
|
|
push first argument
|
|
invoke directive
|
|
remove arguments from the stack
|
|
@end group
|
|
@end example
|
|
|
|
The arguments to RTEMS are typically pushed onto the
|
|
stack using a move instruction with a pre-decremented stack
|
|
pointer as the destination. These arguments must be removed
|
|
from the stack after control is returned to the caller. This
|
|
removal is typically accomplished by adding the size of the
|
|
argument list in bytes to the current stack pointer.
|
|
|
|
@section User-Provided Routines
|
|
|
|
All user-provided routines invoked by RTEMS, such as
|
|
user extensions, device drivers, and MPCI routines, must also
|
|
adhere to these calling conventions.
|
|
|