awk: be more paranoid when freeing loop variable; make code less obfuscated

function                                             old     new   delta
nvfree                                               149     170     +21
next_token                                           928     932      +4
getvar_i                                              95      94      -1
skip_spaces                                           51      45      -6
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/2 up/down: 25/-7)              Total: 18 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

diff --git a/editors/awk.c b/editors/awk.c
index 1d704e8..397d70f 100644 (file)
--- a/editors/awk.c
+++ b/editors/awk.c
@@ -14,6 +14,16 @@
 /* This is a NOEXEC applet. Be very careful! */
 
 
+/* If you comment out one of these below, it will be #defined later
+ * to perform debug printfs to stderr: */
+#define debug_printf_walker(...)  do {} while (0)
+
+#ifndef debug_printf_walker
+# define debug_printf_walker(...) (fprintf(stderr, __VA_ARGS__))
+#endif
+
+
+
 #define        MAXVARFMT       240
 #define        MINNVBLOCK      64
 
@@ -32,6 +42,13 @@
 /* these flags are static, don't change them when value is changed */
 #define        VF_DONTTOUCH    (VF_ARRAY | VF_SPECIAL | VF_WALK | VF_CHILD | VF_DIRTY)
 
+typedef struct walker_list {
+       char *end;
+       char *cur;
+       struct walker_list *prev;
+       char wbuf[1];
+} walker_list;
+
 /* Variable */
 typedef struct var_s {
        unsigned type;            /* flags */
@@ -41,7 +58,7 @@ typedef struct var_s {
                int aidx;               /* func arg idx (for compilation stage) */
                struct xhash_s *array;  /* array ptr */
                struct var_s *parent;   /* for func args, ptr to actual parameter */
-               char **walker;          /* list of array elements (for..in) */
+               walker_list *walker;    /* list of array elements (for..in) */
        } x;
 } var;
 
@@ -913,10 +930,17 @@ static void nvfree(var *v)
                        free(p->x.array);
                }
                if (p->type & VF_WALK) {
-                       //bb_error_msg("free(walker@%p:%p) #1", &p->x.walker, p->x.walker);
-                       free(p->x.walker);
+                       walker_list *n;
+                       walker_list *w = p->x.walker;
+                       debug_printf_walker("nvfree: freeing walker @%p\n", &p->x.walker);
+                       p->x.walker = NULL;
+                       while (w) {
+                               n = w->prev;
+                               debug_printf_walker(" free(%p)\n", w);
+                               free(w);
+                               w = n;
+                       }
                }
-
                clrvar(p);
        }
 
@@ -1724,23 +1748,28 @@ static node *nextarg(node **pn)
 
 static void hashwalk_init(var *v, xhash *array)
 {
-       char **w;
        hash_item *hi;
        unsigned i;
-       char **prev_walker = (v->type & VF_WALK) ? v->x.walker : NULL;
+       walker_list *w;
+       walker_list *prev_walker;
 
-       v->type |= VF_WALK;
+       if (v->type & VF_WALK) {
+               prev_walker = v->x.walker;
+       } else {
+               v->type |= VF_WALK;
+               prev_walker = NULL;
+       }
+       debug_printf_walker("hashwalk_init: prev_walker:%p\n", prev_walker);
 
-       /* walker structure is: "[ptr2end][ptr2start][prev]<word1>NUL<word2>NUL" */
-       w = v->x.walker = xzalloc(2 + 3*sizeof(char *) + array->glen);
-       //bb_error_msg("walker@%p=%p", &v->x.walker, v->x.walker);
-       w[0] = w[1] = (char *)(w + 3);
-       w[2] = (char *)prev_walker;
+       w = v->x.walker = xzalloc(sizeof(*w) + array->glen + 1); /* why + 1? */
+       debug_printf_walker(" walker@%p=%p\n", &v->x.walker, w);
+       w->cur = w->end = w->wbuf;
+       w->prev = prev_walker;
        for (i = 0; i < array->csize; i++) {
                hi = array->items[i];
                while (hi) {
-                       strcpy(w[0], hi->name);
-                       nextword(&w[0]);
+                       strcpy(w->end, hi->name);
+                       nextword(&w->end);
                        hi = hi->next;
                }
        }
@@ -1748,19 +1777,18 @@ static void hashwalk_init(var *v, xhash *array)
 
 static int hashwalk_next(var *v)
 {
-       char **w;
+       walker_list *w = v->x.walker;
 
-       w = v->x.walker;
-       if (w[1] == w[0]) {
-               char **prev_walker = (char**)w[2];
+       if (w->cur >= w->end) {
+               walker_list *prev_walker = w->prev;
 
-               //bb_error_msg("free(walker@%p:%p) #3, restoring to %p", &v->x.walker, v->x.walker, prev_walker);
-               free(v->x.walker);
+               debug_printf_walker("end of iteration, free(walker@%p:%p), prev_walker:%p\n", &v->x.walker, w, prev_walker);
+               free(w);
                v->x.walker = prev_walker;
                return FALSE;
        }
 
-       setvar_s(v, nextword(&w[1]));
+       setvar_s(v, nextword(&w->cur));
        return TRUE;
 }