forked from Imagelibrary/rtems
122 lines
4.2 KiB
Perl
122 lines
4.2 KiB
Perl
@c
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@c COPYRIGHT (c) 1988-1998.
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@c On-Line Applications Research Corporation (OAR).
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@c All rights reserved.
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@c
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@c $Id$
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@c
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@ifinfo
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@node Calling Conventions, Calling Conventions Introduction, CPU Model Dependent Features Floating Point Unit, Top
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@end ifinfo
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@chapter Calling Conventions
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@ifinfo
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@menu
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* Calling Conventions Introduction::
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* Calling Conventions Processor Background::
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* Calling Conventions Calling Mechanism::
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* Calling Conventions Register Usage::
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* Calling Conventions Parameter Passing::
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* Calling Conventions User-Provided Routines::
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@end menu
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@end ifinfo
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@ifinfo
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@node Calling Conventions Introduction, Calling Conventions Processor Background, Calling Conventions, Calling Conventions
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@end ifinfo
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@section Introduction
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Each high-level language compiler generates
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subroutine entry and exit code based upon a set of rules known
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as the compiler's calling convention. These rules address the
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following issues:
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@itemize @bullet
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@item register preservation and usage
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@item parameter passing
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@item call and return mechanism
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@end itemize
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A compiler's calling convention is of importance when
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interfacing to subroutines written in another language either
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assembly or high-level. Even when the high-level language and
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target processor are the same, different compilers may use
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different calling conventions. As a result, calling conventions
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are both processor and compiler dependent.
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@ifinfo
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@node Calling Conventions Processor Background, Calling Conventions Calling Mechanism, Calling Conventions Introduction, Calling Conventions
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@end ifinfo
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@section Processor Background
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The i386 architecture supports a simple yet effective
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call and return mechanism. A subroutine is invoked via the call
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(call) instruction. This instruction pushes the return address
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on the stack. The return from subroutine (ret) instruction pops
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the return address off the current stack and transfers control
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to that instruction. It is is important to note that the i386
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call and return mechanism does not automatically save or restore
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any registers. It is the responsibility of the high-level
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language compiler to define the register preservation and usage
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convention.
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@ifinfo
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@node Calling Conventions Calling Mechanism, Calling Conventions Register Usage, Calling Conventions Processor Background, Calling Conventions
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@end ifinfo
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@section Calling Mechanism
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All RTEMS directives are invoked using a call
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instruction and return to the user application via the ret
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instruction.
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@ifinfo
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@node Calling Conventions Register Usage, Calling Conventions Parameter Passing, Calling Conventions Calling Mechanism, Calling Conventions
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@end ifinfo
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@section Register Usage
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As discussed above, the call instruction does not
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automatically save any registers. RTEMS uses the registers EAX,
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ECX, and EDX as scratch registers. These registers are not
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preserved by RTEMS directives therefore, the contents of these
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registers should not be assumed upon return from any RTEMS
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directive.
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@ifinfo
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@node Calling Conventions Parameter Passing, Calling Conventions User-Provided Routines, Calling Conventions Register Usage, Calling Conventions
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@end ifinfo
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@section Parameter Passing
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RTEMS assumes that arguments are placed on the
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current stack before the directive is invoked via the call
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instruction. The first argument is assumed to be closest to the
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return address on the stack. This means that the first argument
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of the C calling sequence is pushed last. The following
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pseudo-code illustrates the typical sequence used to call a
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RTEMS directive with three (3) arguments:
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@example
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push third argument
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push second argument
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push first argument
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invoke directive
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remove arguments from the stack
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@end example
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The arguments to RTEMS are typically pushed onto the
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stack using a push instruction. These arguments must be removed
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from the stack after control is returned to the caller. This
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removal is typically accomplished by adding the size of the
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argument list in bytes to the stack pointer.
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@ifinfo
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@node Calling Conventions User-Provided Routines, Memory Model, Calling Conventions Parameter Passing, Calling Conventions
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@end ifinfo
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@section User-Provided Routines
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All user-provided routines invoked by RTEMS, such as
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user extensions, device drivers, and MPCI routines, must also
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adhere to these calling conventions.
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