Club Amiga de Montreal - CAM/CAM_CD_1.iso/files/042.lha/assembler/A68k.doc

Text File | 1987-06-25 | 15KB | 340 lines

    A68k - a freely    distributable assembler    for the    Amiga

            by Charlie Gibbs

             with special thanks to
        Brian R. Anderson and Jeff Lydiatt

          (Version 1.00    - June 18, 1987)

Note: This program is NOT Public Domain.  Permission is    given to freely
distribute this    program    provided no fee    is charged, and    this
documentation file is included with the    program.

     This assembler is based on    Brian R. Anderson's 68000 cross-assembler
published in Dr. Dobb's Journal, April through June 1986.  I have converted
it to produce AmigaDOS-format object modules, and have made many enhancements,
such as    macros and include files.

     My    first step was to convert the original Modula-2    code into C.
I did this for two reasons.  First, I had access to a C    compiler, but
not a Modula-2 compiler.  Second, I like C better anyway.

     The executable code generator code    (GetObjectCode and MergeModes) is
essentially the    same as    in the original    article, aside from its    translation
into C.     I have    almost completely rewritten the    remainder of the code,
however, in order to remove restrictions, add enhancements, and    adapt it to
the AmigaDOS environment.  Since the only reference book available to me
was the    AmigaDOS Developer's Manual (Bantam, February 1986), the assembler
and the    remainder of this document work    in terms of that book.


RESTRICTIONS

     Let's get these out of the way first.  There are a few things that I
have not yet implemented, and some outright bugs that would take too long
to correct for this version.

      o    The verification file (-v) option is not supported.  Diagnostic
    messages always    appear on the console.    They also appear in the
    listing    file, however (see extensions below).

      o    The header file    (-h) option is not supported.

      o    The equate file    (-e) option is not supported.  If someone manages
    to explain to me just what it does, and    convinces me that it's
    sufficiently useful, I might implement it.

      o    The file names in the include directory    list (-i) must be separated
    by commas.  The    list may not be    enclosed in quotes.

      o    Labels assigned    by EQUR    and REG    directives are case-sensitive.

      o    The following directives are not supported, and    will be    flagged    as
    invalid    op-codes:

        RORG
        OFFSET
        NOPAGE
        LLEN
        PLEN
        NOOBJ
        FAIL
        FORMAT
        NOFORMAT
        MASK2

    I feel that NOPAGE, LLEN, and PLEN should not be defined within    a
    source module.    It doesn't make sense to me to have to change your
    program    just because you want to print your listings on    different
    paper.    The command-line option    "-p" (see below) can be used as a
    replacement for    PLEN.


EXTENSIONS

     Now for the good stuff:

      o    Labels can be any length that will fit onto one    source line
    (currently 128 bytes maximum).    Since labels are stored    on the
    heap, the number of labels that    can be processed is limited only
    by available memory, which can be increased by using the "-w"
    option (see below).

      o    Since section data and user macro definitions are stored on the
    same heap as the symbol    table (see above), they    too are    limited
    only by    available memory.  (Actually, there is a hard-coded limit
    of 32767 sections, but I doubt anyone will run into that one.)

      o    The only values    a label    cannot take are    the register names - the
    assembler can distinguish between the same name    used as    a label,
    instruction name, macro    name, directive, or section name.

      o    Section    and user macro names appear in the symbol table    dump, and
    will also be cross-referenced.    Their names can    be the same as any
    label (see above); the assembler can sort them out.

      o    Includes and macro calls can be    nested indefinitely, limited only
    by available memory.  The message "Secondary heap overflow -
    assembly terminated" will be displayed if memory is exhausted.
    You can    increase the size of this heap using the -w parameter
    (see below).  Recursive    macros are supported; recursive    includes
    will, of course, result    in a loop that will be broken only when
    the heap overflows.

      o    The EVEN directive forces alignment on a word (2-byte) boundary.
    It does    the same thing as CNOP 0,2.
    (This one is left over from the    original code.)

      o    Branch (Bcc) instructions to a previously-defined label    will be
    automatically converted    to short form if possible.  This feature is
    not available for forward branches, since in pass 1 the    assembler
    doesn't yet know how far the branch must go.

      o    If a MOVEM instruction only specifies one register, it is converted
    to the corresponding MOVE instruction.    Instructions of    the form
    MOVEM D0-D0,label will not be converted, however.

      o    ADD, SUB, and MOVE instructions    will be    converted to ADDQ, SUBQ,
    and MOVEQ respectively if possible.  Instructions coded    explicitly
    as (for    example) ADDA or ADDI will not be converted.

      o    ADD, CMP, SUB, and MOVE    to an address register are converted to
    ADDA, CMPA, SUBA, and MOVEA respectively, except if an ADD, SUB,
    or MOVE    instruction has    already    been convreted to quick    form.

      o    ADD, AND, CMP, EOR, OR,    and SUB    of an immediate    value are converted
    to ADDI, ANDI, CMPI, EORI, ORI,    and SUBI respectively (unless the
    address    register or quick conversion above has already been done).

      o    If both    operands of a CMP instruction are postincrement    mode, the
    instruction is converted to CMPM.

      o    The SECTION directive allows a third parameter.     This can be
    specified as either CHIP or FAST (upper- or lower-case).  If this
    parameter is present, the hunk will be written with the    MEMF_CHIP
    or MEMF_FAST bit set.  This allows you to produce "pre-ATOMized"
    object modules.

      o    The synonyms DATA and BSS are accepted for SECTION directives
    starting data or BSS hunks.  A section name is mandatory for
    all non-CODE hunks.

      o    The ability to produce Motorola    S-records is retained from the
    original code.    The -s option causes the assembler to produce
    S-format instead of AmigaDOS format.  Relocatable code cannot be
    produced in this format.

      o    Error messages include the name    of the source, macro, or include
    module that contains the statement in error, plus the line number
    within the module of the offending line.  If a statement has
    multiple errors, this information appears only on the first
    error message for the statement.


HOW TO USE IT

     The command-line syntax to    run the    assembler is as    follows:

    a68k <source file>
        [-o<object file>]
        [-l<listing file>]
        [-i<include dirlist>]
        [-p<page depth>]
        [-d]
        [-s]
        [-w[<primary-heap-size>][,secondary-heap-size]]
        [-x]

These options can be given in any order, so if you like    to specify your
switches first,    you can.  Option values, if any, must immediately follow
the keyword with no intervening    spaces.

     If    the -o keyword is omitted, the object file will    be given a default
name.  It is created by    replacing all characters after the last    period in
the source file    name by    "o".  For example, if the source file name is
"myprog.asm", the object file name defaults to "myprog.o".  A source name
of "my.new.prog.asm" produces a default object file name of "my.new.prog.o".
If the source file name    does not contain a period, ".o" is appended to it
to produce the default object file name.

     The default value for the listing file name is arrived at in the same
way as the object file name, except that ".lst" is appended instead of ".o".
If you don't specify this parameter, no listing file will be produced.
If you specify -x (see below), -l (with    the default name) is assumed,
although you can still use this    parameter if you wish.

     The include directory list    is a list of directory names separated by
commas.     No embedded blanks are    allowed.  For example, the specification
    -imylib,df1:another.lib
will cause include files to be searched    for first in the current directory,
then in    "mylib", then in "df1:another.lib".

     The -d keyword causes symbol table    entries    (hunk_symbol) to be written
to the object module for the use of symbolic debuggers.

     The -p keyword causes the page depth to be    set to the specified value.
If omitted, a default of 60 lines (-p60) is assumed.

     The -s keyword, if    specified, causes the object file to be    written    in
Motorola S-record format.  If omitted, AmigaDOS    format will be produced.
The default name for an    S-record file has ".s" appended to the source name,
rather than ".o"; this can still be overridden with the -o keyword, though.

     The -w keyword specifies the size of the heaps used.  The primary heap
stores the symbol table, user macro text, relocation information, and
cross-reference    information.  The secondary heap stores    information for
nested macro calls and include files.  The primary heap    size defaults to
32768 bytes, which should be enough for    all but    the largest assemblies.
The secondary heap size    defaults to 1024 bytes,    which should be    enough
unless you use very deeply nested macros and/or    include    files with long
path names.  You can specify either or both parameters.     For example:
    -w40000        secondary heap size remains at 1024 bytes
    -w,2000        primary    heap size remains at 32768 bytes
    -w40000,2000    increases the size of both heaps
If you're really tight for memory, and are assembling small modules, you
can use    this keyword to    shrink the heaps below their default sizes.
At the end of an assembly, a message will be displayed giving the
amount of heap space actually used, in the form    of the -w command
you would have to enter    to allocate the    mininum    heap space.
See below for a    layout of the heaps.

     The -x keyword will cause the symbol table    dump to    include
cross-reference    information.  If you haven't also specified -l (with
or without a file name), -l with the default file name will be assumed.


     If    you wish to override the default object    and (optionally) listing
file names, you    can omit the -o    and -l keywords.  The assembler    interprets
the first three    parameters without leading hyphens as the source, object,
and listing file names respectively.  Anything over three file names is    an
error, as is attempting    to respecify a file name with the -o or    -l keywords.


     The primary heap is built from both ends.    Symbol table entries
(including labels) and macro text are stored during pass 1.  Cross-reference
data is    stored during pass 2.  Relocation information is also stored during
pass 2,    but is cleared at the end of each SECTION.  Since it is    no longer
needed once dumped, the    space is freed for re-use by the next section's
relocation information.     The expression    parser also uses the primary heap
to store its working stacks - this space is freed as soon as an    expression
has been evaluated.
     The fixed portion of each symbol table entry occupies 16 bytes.  The
labels and macro text occupy just enough space to hold their strings
(including the end-of-string delimiter)    - they are all pointed to by fixed
symbol table entries.  Relocation entries occupy 10 bytes each.
Cross-reference    entries    are 12 bytes long - each holds four references to
one symbol.  The expression parser creaates temporary entries for terms
(10 bytes each)    and operators (4 bytes each).  Since terms are combined
as soon    as possible, the parser    almost never needs to store the    entire
expression on the heap.
     The diagram below illustrates the layout of the primary heap.  High
memory addresses are at    the top    of the diagram,    while low addresses are
at the bottom.    The names on the left of the diagram are the names of the
pointers to the    various    tables within the heap.

    Heap + maxheap ------------->  ___________________________
                      |                  |
                      |      Symbol table          |
    struct SymTab *SymStart     ---> |___________________________|
                      |                  |
                      |      Symbol references      |
    struct Ref *RefStart -------> |___________________________|
                      |                  |
                      |      (unused space)      |
    char *HeapLim --------------> |___________________________|
                      |                  |
                      |      Relocation data      |
    struct RelTab *RelStart    ----> |___________________________|
                      |                  |
                      |      Labels and macro text      |
    char *Heap -----------------> |___________________________|

     Note that the pointers are    to various types.  This    makes for
lots of    interesting casts.  (Ain't C fun?)  Since the relocation
data is    cleared    at the end of each section, HeapLim will move up and
down.  The "high-water mark" is stored in char *HighHeap, which is
used solely to produce the memory usage    message    at the end of the
assembly.  Note    that a program may consist of a    section    containing
many relocatable references, followed by a section with    fewer
relocatable references but lots    of symbol references.  In this case,
RefStart might end up below HighHeap, and the final message would
indicate that more heap    space was used than was    available.  This is
not an error - only if RefStart    hits HeapLim will an error be reported.


     The secondary heap    is also    built from both    ends, but it grows and
shrinks    according to how many macros and include files are currently open.
At all times there will    be at lease one    entry on the heap, for the original
source code file.
     The bottom    of the heap holds the names of the source code file and
any macro or include files that    are currently open .  The full path is
given.    A null string is stored    for user macros.  Macro    arguments are
stored by additional strings, one for each argument in the macro call line.
All strings are    stored in minimum space, similar to the    labels and user
macro text on the primary heap.     File names are    pointed    to by the fixed
table entries (see below) - macro arguments are    accessed by stepping past
the macro name to the desired argument,    unless NARG would be exceeded.
     The fixed portion of the heap is built down from the top.    Each entry
occupies 16 bytes.  Enough information is stored to return to the proper
position in the    outer file once    the current macro or include file has been
completely processed.
     The diagram below illustrates the layout of the secondary heap.

    Heap2 +    maxheap2 ----------->  ___________________________
                      |                  |
                      |      Input    file table      |
    struct InFCtl *InF ---------> |___________________________|
                      |                  |
                      |      Parser operator stack      |
    struct OpStack *Ops --------> |___________________________|
                      |                  |
                      |      (unused space)      |
    struct TermStack *Term -----> |___________________________|
                      |                  |
                      |      Parser term stack      |
    char *NextFNS --------------> |___________________________|
                      |                  |
                      |      Input    file name stack      |
    char *Heap2 ----------------> |___________________________|

     The "high-water mark" for NextFNS is stored in char *High2,
and the    "low-water mark" (to stretch a metaphor) for InF is stored
in struct InFCtl *LowInF.  Again, these    figures    are used only to
determine the maximum heap usage.


     Please send me any    bug reports, flames, etc.  I can be reached on
Dorean BBS (604/432-8579), Mind    Link (604/533-2312), at    any Panorama
(PAcific NORthwest AMiga Association) meeting, or via Jeff Lydiatt
or Larry Phillips.  (I don't have the time or money to live on
Usenet or CompuServe, etc.)

                Charlie    Gibbs
                #21 - 21555 Dewdney Trunk Road
                Maple Ridge, B.C.  CANADA
                V2X 3G6


P.S.  COMING SOON TO AN    AMIGA NEAR YOU:     68010/68020 support!