README.md

MMIX support library for various purposes

How to compile and run mmix programs

• TODO: mmix-ld

• TODO: Compilation pipeline

• TODO: bin/

• TODO: binfmt

Dynamic memory allocation in :PoolSegment

The heap will be organized as memory blocks inside the pool segment of the executable. This needs some cooperation from the user: The convention (as defined by the mmixware documentation) is that M_8[:Pool_Segment] points to the first unallocated region within the pool address space. User programs utilizing address space from the pool segment must obey this rule by 'allocating' memory by modifying M_8[:Pool_Segment] appropriately. The library assumes that this pointer is OCTA aligned.

The temporary registers $255 and :MM:t

• Neither mmixal, nor GNU guarantee that the contents of the temporary register $255 is preserved after a JMP, PUSHJ instruction, or LDA pseudo instruction. The assembler is free to use $255 to construct an absolute address if the target label cannot be reached by a near jump. Thus, when calling a library subroutine the contents of $255 might not be preserved.

• Similarly, the library might use :MM:t internally. Thus, when calling a library subroutine - even a non G-variant - the contents of :MM:t might not be preserved. (Subroutines generally try to preserve the contents of :MM:t, though).

Global register usage

The library avoids unnecessary allocation of global registers by not using LDA instructions at the expense of a slight runtime overhead. The library allocates 3 global registers (GREGs) for internal use and an additional global register :MM:t for calling library routines (see next section).

Calling convention and error handling

Suroutines come in a number of different variants.

• Subroutines without a trailing J, will terminate the program with an error message (or call an error handler if specified). Variants with a trailing J, will jump to :rJ+#4 on succes and to :rJ+#0 on failure (some variants that would return a boolean value jump to :rJ+#4 for true and to :rJ+#0 for false instead.) This can be used to implement customized error handling. An example:

            % Try to allocate a block of memory:
            SET         $1,[...]
            PUSHJ       $0,:MM:Pool:AllocJ
            JMP         1F
            ... % Allocation was successful, continue normally.

     1H     ... % Allocation failed, error handling.

• Subroutines that have at most one argument and at most one return parameter come also in a variant with a trailing G which indicates that values are passed through the library specific temporary global register :MM:t. An example:

            % Try to allocate a block of memory:
t           IS          :MM:t
            SET         t,[...]
            PUSHJ       t,:MM:Pool:AllocG
                        % Address of allocated memory in t

Copying

Copyright (C) 2013-2018 Matthias Maier <[email protected]>

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