Info Catalog as: MMIX-Syntax as: MMIX-Dependent

as: MMIX-mmixal

 
 9.27.4 Differences to 'mmixal'
 ------------------------------
 
 The binutils 'as' and 'ld' combination has a few differences in function
 compared to 'mmixal' (mmixsite).
 
    The replacement of a symbol with a GREG-allocated register (
 GREG-base) is not handled the exactly same way in 'as' as in 'mmixal'.
 This is apparent in the 'mmixal' example file 'inout.mms', where
 different registers with different offsets, eventually yielding the same
 address, are used in the first instruction.  This type of difference
 should however not affect the function of any program unless it has
 specific assumptions about the allocated register number.
 
    Line numbers (in the 'mmo' object format) are currently not
 supported.
 
    Expression operator precedence is not that of mmixal: operator
 precedence is that of the C programming language.  It's recommended to
 use parentheses to explicitly specify wanted operator precedence
 whenever more than one type of operators are used.
 
    The serialize unary operator '&', the fractional division operator
 '//', the logical not operator '!' and the modulus operator '%' are not
 available.
 
    Symbols are not global by default, unless the option
 '--globalize-symbols' is passed.  Use the '.global' directive to
 globalize symbols (Global).
 
    Operand syntax is a bit stricter with 'as' than 'mmixal'.  For
 example, you can't say 'addu 1,2,3', instead you must write 'addu
 $1,$2,3'.
 
    You can't LOC to a lower address than those already visited (i.e.,
 "backwards").
 
    A LOC directive must come before any emitted code.
 
    Predefined symbols are visible as file-local symbols after use.  (In
 the ELF file, that is--the linked mmo file has no notion of a file-local
 symbol.)
 
    Some mapping of constant expressions to sections in LOC expressions
 is attempted, but that functionality is easily confused and should be
 avoided unless compatibility with 'mmixal' is required.  A LOC
 expression to '0x2000000000000000' or higher, maps to the '.data'
 section and lower addresses map to the '.text' section (
 MMIX-loc).
 
    The code and data areas are each contiguous.  Sparse programs with
 far-away LOC directives will take up the same amount of space as a
 contiguous program with zeros filled in the gaps between the LOC
 directives.  If you need sparse programs, you might try and get the
 wanted effect with a linker script and splitting up the code parts into
 sections (Section).  Assembly code for this, to be compatible
 with 'mmixal', would look something like:
       .if 0
       LOC away_expression
       .else
       .section away,"ax"
       .fi
    'as' will not execute the LOC directive and 'mmixal' ignores the
 lines with '.'.  This construct can be used generally to help
 compatibility.
 
    Symbols can't be defined twice-not even to the same value.
 
    Instruction mnemonics are recognized case-insensitive, though the
 'IS' and 'GREG' pseudo-operations must be specified in upper-case
 characters.
 
    There's no unicode support.
 
    The following is a list of programs in 'mmix.tar.gz', available at
 <http://www-cs-faculty.stanford.edu/~knuth/mmix-news.html>, last checked
 with the version dated 2001-08-25 (md5sum
 c393470cfc86fac040487d22d2bf0172) that assemble with 'mmixal' but do not
 assemble with 'as':
 
 'silly.mms'
      LOC to a previous address.
 'sim.mms'
      Redefines symbol 'Done'.
 'test.mms'
      Uses the serial operator '&'.
 

Info Catalog as: MMIX-Syntax as: MMIX-Dependent