swapforth

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#include <stdio.h>
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#include <stdint.h>
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#include <inttypes.h>
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#include <string.h>
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#include <stdlib.h>
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#include <sys/mman.h>
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// These are Forth-callable C functions
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// SwapForth is passed the array CFUNCS, so it knows the
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// address of each of function at run-time.
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//
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// This means that SwapForth itself does not refer to any
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// external symbols, so it can be relocated with memcpy().
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typedef size_t cell_t;
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void _dotx(cell_t x)
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{
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  printf("%016zx ", x);
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}
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void _bye()
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{
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  exit(0);
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}
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void _emit(char c)
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{
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  putchar(c);
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  fflush(stdout);
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}
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int _key()
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{
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  return getchar();
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}
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static const size_t cfuncs[] = {
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  (size_t)_dotx,
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  (size_t)_bye,
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  (size_t)_emit,
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  (size_t)_key
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};
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#define MEMSIZE (1024 * 1024)
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int main()
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{
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  extern unsigned char swapforth, swapforth_ends;
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  // allocate executable memory via sys call
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  void* mem = mmap(NULL, MEMSIZE, PROT_READ | PROT_WRITE | PROT_EXEC, MAP_PRIVATE | MAP_ANON, -1, 0);
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  // copy runtime code into allocated memory
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  memcpy(mem, &swapforth, &swapforth_ends - &swapforth);
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  printf("swapforth = %p\n", &swapforth);
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  printf("mem       = %p\n", mem);
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  // typecast allocated memory to a function pointer
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  int64_t (*func) () = mem;
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  int64_t stack[512 + 500];
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  cell_t r = func(stack + 512, cfuncs);
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  printf("(%p, %p)\n", stack + 512, cfuncs);
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  printf("r = %zx\n", r);
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  // printf("\ndepth = %d\n", (int)((stack + 512) - (int64_t*)r));
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  // Free up allocated memory
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  munmap(mem, MEMSIZE);
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  return 0;
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}
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