Data commit

Task/Machine-code/Cowgol/machine-code.cowgol

@@ -0,0 +1,32 @@
+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();