sandbox/misc/kforth/doc/part-0x09.rst

Write You a Forth, 0x03
-----------------------

:date: 2018-03-09 13:10
:tags: wyaf, forth

So the last post had some issues and I hadn't updated the front end to use the
new tooling. I removed the arena and switched to the internal dictionary::

        #include "defs.h"
        #include "eval.h"
        #include "stack.h"
        #include "word.h"

        #include <stdio.h>
        #include <stdlib.h>
        #include <string.h>

        void
        hello(void)
        {
                printf("hello, world\n");
        }

        int
        main(void)
        {
                dstack_push(2);
                dstack_push(3);

                append_native_word("hello", 5, hello);
                uintptr_t	hwb = 0;

                if (!lookup("hello", 5, &hwb)) {
                        fprintf(stderr, "failed to lookup 'hello'\n");
                        exit(1);
                }
                printf("hello: 0x%lx\n", (unsigned long)hwb);
                if (!execute("hello", 5)) {
                        fprintf(stderr, "failed to execute 'hello'\n");
                        exit(1);
                }

                printf("finished\n");
        }

Also, there's a (not-so) subtle bug in ``word.c``: the header is overwritten by the function
body, which is the path to segfaulting. I've also added an offset variable to make tracking
the offset easier::

        void
        store_native(uint8_t *entry, const char *name, const uint8_t len, void(*target)(void))
        {
                uintptr_t       target_p = (uintptr_t)target;
        -       size_t          link = 2 + len + (2 * sizeof(uintptr_t));
        +       size_t          offset = 2 + len + sizeof(size_t);
        +       size_t          link = offset + (2 * sizeof(uintptr_t));
        
                /* write the header */
                entry[0] = len;
        @@ -45,8 +66,9 @@ store_native(uint8_t *entry, const char *name, const uint8_t len, void(*target)(
                memcpy(entry+2+len, &link, sizeof(link));
        
                /* write the native executor codeword and the function pointer */
        -       memcpy(entry, (uint8_t *)(&nexec_p), sizeof(uintptr_t));
        -       memcpy(entry + sizeof(uintptr_t), (uint8_t *)(&target_p), sizeof(uintptr_t));
        +       memcpy(entry+offset, (uint8_t *)(&nexec_p), sizeof(uintptr_t));
        +       offset += sizeof(uintptr_t);
        +       memcpy(entry+offset, (uint8_t *)(&target_p), sizeof(uintptr_t));
        }

The header file ``word.h`` didn't contain ``append_native_word``, ``lookup``,
or ``execute``, so that gets updated too. The end result is::

        $ ./kf-default     
        hello: 0x6cbc6f
        hello, world
        finished

As usual, the code is tagged with `part-0x09 <https://github.com/kisom/kforth/tree/part-0x09>`_.