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(as.info)MMIX-Symbols

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Symbols
.......

   The character `:' is permitted in identifiers.  There are two
exceptions to it being treated as any other symbol character: if a
symbol begins with `:', it means that the symbol is in the global
namespace and that the current prefix should not be prepended to that
symbol (Note: MMIX-prefix).  The `:' is then not considered part of
the symbol.  For a symbol in the label position (first on a line), a `:'
at the end of a symbol is silently stripped off.  A label is permitted,
but not required, to be followed by a `:', as with many other assembly
formats.

   The character `@' in an expression, is a synonym for `.', the
current location.

   In addition to the common forward and backward local symbol formats
(Note: Symbol Names), they can be specified with upper-case `B' and
`F', as in `8B' and `9F'.  A local label defined for the current
position is written with a `H' appended to the number:
     3H LDB $0,$1,2
   This and traditional local-label formats cannot be mixed: a label
must be defined and referred to using the same format.

   There's a minor caveat: just as for the ordinary local symbols, the
local symbols are translated into ordinary symbols using control
characters are to hide the ordinal number of the symbol.
Unfortunately, these symbols are not translated back in error messages.
Thus you may see confusing error messages when local symbols are used.
Control characters `\003' (control-C) and `\004' (control-D) are used
for the MMIX-specific local-symbol syntax.

   The symbol `Main' is handled specially; it is always global.

   By defining the symbols `__.MMIX.start..text' and
`__.MMIX.start..data', the address of respectively the `.text' and
`.data' segments of the final program can be defined, though when
linking more than one object file, the code or data in the object file
containing the symbol is not guaranteed to be start at that position;
just the final executable.  Note: MMIX-loc.