include "cowgol.coh";

# Run machine code at cptr, given two 32-bit arguments,
# return the value returned from EAX.
sub RunCode(cptr: [uint8], arg1: uint32, arg2: uint32): (rslt: uint32) is
    # Inline assembly is supported, so this whole rigmarole
    # is not even necessary.
    # Though note that this (obviously) depends on the assembly back-end used.
    # Linux as uses AT&T syntax, so that's what I'm doing here.
    # Cowgol supports many processors but this will, obviously, only work
    # on x86.

    @asm "pushl (",arg1,")";      # Push the two arguments on the stack
    @asm "pushl (",arg2,")";
    @asm "call *(",cptr,")";      # Call the code at the pointer
    @asm "movl %eax, (",rslt,")"; # Store the result in rslt
    @asm "popl %eax";             # Clean up the stack
    @asm "popl %eax";
end sub;

# Store code in an array. This is enough to make it available.
var code: uint8[] := {139, 68, 36, 4, 3, 68, 36, 8, 195};

# Use the function
print_i32(RunCode(&code as [uint8], 7, 12)); # this prints 7+12 = 19
print_nl();

# As a demonstration, this shows it can be patched at runtime to multiply instead
code[4] := 247;
code[5] := 100;
print_i32(RunCode(&code as [uint8], 7, 12)); # this prints 7*12 = 84
print_nl();