Ravenbrook / Projects / Memory Pool System / Version 1.111 Product Sources / Design Documents

Memory Pool System Project

                 STACK SCANNER FOR DIGITAL UNIX / ALPHA SYSTEMS
                               design.mps.sso1al
                                   draft doc
                                 drj 1997-03-27

    INTRODUCTION

    .readership: Any MPS developer.

    .intro: This is the design for Stack Scanner module that runs on DIGITAL UNIX /
    Alpha systems (See os.o1 and arch.al).  The design adheres to the general
    design and interface described (probably not described actually) in
    design.mps.ss.

    .source.alpha: book.digital96 (Alpha Architecture Handbook) describes the Alpha
    Architecture independently of any particular implementation.  The instruction
    mnemonics and the semantics for each instruction are specified in that document.
    .source.as:
    <URL:http://www.partner.digital.com/www-swdev/pages/Home/TECH/documents/Digital_
    UNIX/V4.0/AA-PS31D-TET1_html/TITLE.html> (Assembly Language Programmer's Guide)
    describes the assembler syntax and assembler directives.  It also summarises
    the calling conventions used.  Chapters 1 and 6 were especially useful,
    especially chapter 6.
    .source.convention:
    <URL:http://www.partner.digital.com/www-swdev/pages/Home/TECH/documents/Digital_
    UNIX/V4.0/AA-PY8AC-TET1_html/TITLE.html> (Calling Standard for Alpha Systems)
    describes the calling conventions used for Digital Alpha systems.  Chapter 2 was
    useful.  But the whole document was not used as much as the previous 2
    documents.

    DEFINITIONS

    .def.saved: Saved Register.  A saved register is one whose value is defined to
    be preserved across a procedure call according to the Calling Standard.  They
    are $9-$15, $26, and $30.  $30 is the stack pointer.
    .def.non-saved: Non-Saved Register.  A non-save register is a register that is
    assumed to be modified across a procedure call according to the Calling
    Standard.
    .def.tos: Top of Stack.  The top of stack is the youngest portion of the stack.
    .def.bos: Bottom of Stack.  The bottom of stack is the oldest portion of the
    stack.
    .def.base: Base.  Of a range of addresses, the base is the lowest address in
    the range.
    .def.limit: Limit.  Of a range of addresses, the limit is "one past" the
    highest address in the range.

    OVERVIEW

    .overview: The registers and the stack need to be scanned.  This is achieved by
    storing the contents of the registers into a frame at the top of the stack and
    then passing the base and limit of the stack region, including the newly
    created frame, to the function TraceScanAreaTagged.  TraceScanAreaTagged
    performs the actual scanning and fixing.

    DETAIL DESIGN

    Functions

    .fun.stackscan:

    Res StackScan(ScanState ss, Addr *StackBot);

    .fun.stackscan.asm: The function is written in assembler.
    .fun.stackscan.asm.justify: This is because the machine registers need to be
    examined, and it is only possible to access the machine registers using
    assembler.
    .fun.stackscan.entry: On entry to this procedure all the non-saved (temporary)
    registers that contain live pointers must have been saved in some root (usually
    the stack) by the mutator (otherwise it would lose the values).  Therefore only
    the saved registers need to be stored by this procedure.
    .fun.stackscan.assume.saved: We assume that all the saved registers are roots.
    This is conservative since some of the saved registers might not be used.
    .fun.stackscan.frame: A frame is be created on the top of the stack.
    .fun.stackscan.frame.justify: This frame is used to store the saved registers
    into so that they can be scanned.
    .fun.stackscan.save: All the saved registers, apart from $30 the stack pointer,
    are to be stored in the frame.  .fun.stackscan.save.justify: This is so that
    they can be scanned.  The stack pointer itself is not scanned as the stack is
    assumed to be a root (and therefore a priori alive).
    .fun.stackscan.call: TraceScanAreaTagged is called with the current stack
    pointer as the base and the (passed in) StackBot as the limit of the region to
    be scanned.   .fun.stackscan.call.justify: This function does the actual
    scanning.  The Stack on Alpha systems grows down so the stack pointer (which
    points to the top of the stack) is lower in memory than the bottom of the stack.
    .fun.stackscan.return: The return value from TraceScanAreaTagged is used as the
    return value for StackScan.

## A. References

## B. Document History

2002-06-07 | RB | Converted from MMInfo database design document.

## C. Copyright and License

This document is copyright © 1995-2002 Ravenbrook Limited. All rights reserved. This is an open source license. Contact Ravenbrook for commercial licensing options.

Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
3. Redistributions in any form must be accompanied by information on how to obtain complete source code for the this software and any accompanying software that uses this software. The source code must either be included in the distribution or be available for no more than the cost of distribution plus a nominal fee, and must be freely redistributable under reasonable conditions. For an executable file, complete source code means the source code for all modules it contains. It does not include source code for modules or files that typically accompany the major components of the operating system on which the executable file runs.

This software is provided by the copyright holders and contributors "as is" and any express or implied warranties, including, but not limited to, the implied warranties of merchantability, fitness for a particular purpose, or non-infringement, are disclaimed. In no event shall the copyright holders and contributors be liable for any direct, indirect, incidental, special, exemplary, or consequential damages (including, but not limited to, procurement of substitute goods or services; loss of use, data, or profits; or business interruption) however caused and on any theory of liability, whether in contract, strict liability, or tort (including negligence or otherwise) arising in any way out of the use of this software, even if advised of the possibility of such damage.

`$Id: //info.ravenbrook.com/project/mps/version/1.111/design/sso1al/index.html#2 $`

Ravenbrook / Projects / Memory Pool System / Version 1.111 Product Sources / Design Documents