forked from Imagelibrary/rtems
8d7393ad5f
* BSP_TIMES, ChangeLog, Makefile.am, arm.texi, bsp.t, callconv.t, cpumodel.t, cputable.t, fatalerr.t, intr_NOTIMES.t, memmodel.t, preface.texi, stamp-vti, timeBSP.t, timing.texi, version.texi, wksheets.texi: New files as ARM supplement initial version added.
74 lines
2.5 KiB
Perl
74 lines
2.5 KiB
Perl
@c
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@c COPYRIGHT (c) 1988-2002.
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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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@chapter Calling Conventions
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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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@section Processor Background
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The ARM architecture supports a simple yet
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effective call and return mechanism. A subroutine is invoked
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via the branch and link (@code{bl}) instruction. This instruction
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saves the return address in the @code{lr} register. Returning
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from a subroutine only requires that the return address be
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moved into the program counter (@code{pc}), possibly with
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an offset. It is is important to
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note that the @code{bl} instruction does not
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automatically save or restore any registers. It is the
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responsibility of the high-level language compiler to define the
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register preservation and usage convention.
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@section Calling Mechanism
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All RTEMS directives are invoked using the @code{bl}
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instruction and return to the user application via the
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mechanism described above.
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@section Register Usage
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As discussed above, the ARM's call and return mechanism dos
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not automatically save any registers. RTEMS uses the registers
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@code{r0}, @code{r1}, @code{r2}, and @code{r3} as scratch registers and
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per ARM calling convention, the @code{lr} register is altered
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as well. These registers are not preserved by RTEMS directives
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therefore, the contents of these registers should not be assumed
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upon return from any RTEMS directive.
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@section Parameter Passing
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RTEMS assumes that ARM calling conventions are followed and that
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the first four arguments are placed in registers @code{r0} through
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@code{r3}. If there are more arguments, than that, then they
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are place on the stack.
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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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