commit 9795a1801eb1a4f3ae6346e32666d3d05f006115

Author: Siddhesh Poyarekar <siddhesh@redhat.com>

Date:   Sun Jun 30 20:45:05 2013 +0530

    Fall back to non-cached sequence traversal and comparison

    strcoll currently falls back to alloca if malloc fails, resulting in a

    possible stack overflow.  This patch implements sequence traversal and

    comparison without caching indeces and rules.

diff --git a/string/strcoll_l.c b/string/strcoll_l.c

index 1bb9e23..1be6874 100644

--- a/string/strcoll_l.c

+++ b/string/strcoll_l.c

@@ -55,6 +55,12 @@ typedef struct

   const USTRING_TYPE *us;	/* The string.  */

   int32_t *idxarr;		/* Array to cache weight indeces.  */

   unsigned char *rulearr;	/* Array to cache rules.  */

+  unsigned char rule;		/* Saved rule for the first sequence.  */

+  int32_t idx;			/* Index to weight of the current sequence.  */

+  int32_t save_idx;		/* Save looked up index of a forward

+				   sequence after the last backward

+				   sequence.  */

+  const USTRING_TYPE *back_us;	/* Beginning of the backward sequence.  */

 } coll_seq;

 /* Get next sequence.  The weight indeces are cached, so we don't need to

@@ -227,7 +233,191 @@ get_next_seq (coll_seq *seq, int nrules, const unsigned char *rulesets,

   seq->us = us;

 }

-/* Compare two sequences.  */

+/* Get next sequence.  Traverse the string as required.  This function does not

+   set or use any index or rule cache.  */

+static void

+get_next_seq_nocache (coll_seq *seq, int nrules, const unsigned char *rulesets,

+		      const USTRING_TYPE *weights, const int32_t *table,

+		      const USTRING_TYPE *extra, const int32_t *indirect,

+		      int pass)

+{

+#include WEIGHT_H

+  int val = seq->val = 0;

+  int len = seq->len;

+  size_t backw_stop = seq->backw_stop;

+  size_t backw = seq->backw;

+  size_t idxcnt = seq->idxcnt;

+  size_t idxmax = seq->idxmax;

+  int32_t idx = seq->idx;

+  const USTRING_TYPE *us = seq->us;

+

+  while (len == 0)

+    {

+      ++val;

+      if (backw_stop != ~0ul)

+	{

+	  /* The is something pushed.  */

+	  if (backw == backw_stop)

+	    {

+	      /* The last pushed character was handled.  Continue

+		 with forward characters.  */

+	      if (idxcnt < idxmax)

+		{

+		  idx = seq->save_idx;

+		  backw_stop = ~0ul;

+		}

+	      else

+		{

+		  /* Nothing anymore.  The backward sequence ended with

+		     the last sequence in the string.  Note that len is

+		     still zero.  */

+		  idx = 0;

+		  break;

+	        }

+	    }

+	  else

+	    {

+	      /* XXX Traverse BACKW sequences from the beginning of

+		 BACKW_STOP to get the next sequence.  Is ther a quicker way

+	         to do this?  */

+	      int i = backw_stop;

+	      us = seq->back_us;

+	      while (i < backw)

+		{

+		  int32_t tmp = findidx (&us, -1);

+		  idx = tmp & 0xffffff;

+		  i++;

+		}

+	      --backw;

+	      us = seq->us;

+	    }

+	}

+      else

+	{

+	  backw_stop = idxmax;

+	  int32_t prev_idx = idx;

+

+	  while (*us != L('\0'))

+	    {

+	      int32_t tmp = findidx (&us, -1);

+	      unsigned char rule = tmp >> 24;

+	      prev_idx = idx;

+	      idx = tmp & 0xffffff;

+	      idxcnt = idxmax++;

+

+	      /* Save the rule for the first sequence.  */

+	      if (__glibc_unlikely (idxcnt == 0))

+	        seq->rule = rule;

+

+	      if ((rulesets[rule * nrules + pass]

+		   & sort_backward) == 0)

+		/* No more backward characters to push.  */

+		break;

+	      ++idxcnt;

+	    }

+

+	  if (backw_stop >= idxcnt)

+	    {

+	      /* No sequence at all or just one.  */

+	      if (idxcnt == idxmax || backw_stop > idxcnt)

+		/* Note that len is still zero.  */

+		break;

+

+	      backw_stop = ~0ul;

+	    }

+	  else

+	    {

+	      /* We pushed backward sequences.  If the stream ended with the

+		 backward sequence, then we process the last sequence we

+		 found.  Otherwise we process the sequence before the last

+		 one since the last one was a forward sequence.  */

+	      seq->back_us = seq->us;

+	      seq->us = us;

+	      backw = idxcnt;

+	      if (idxmax > idxcnt)

+		{

+		  backw--;

+		  seq->save_idx = idx;

+		  idx = prev_idx;

+		}

+	      if (backw > backw_stop)

+		backw--;

+	    }

+	}

+

+      len = weights[idx++];

+      /* Skip over indeces of previous levels.  */

+      for (int i = 0; i < pass; i++)

+	{

+	  idx += len;

+	  len = weights[idx];

+	  idx++;

+	}

+    }

+

+  /* Update the structure.  */

+  seq->val = val;

+  seq->len = len;

+  seq->backw_stop = backw_stop;

+  seq->backw = backw;

+  seq->idxcnt = idxcnt;

+  seq->idxmax = idxmax;

+  seq->us = us;

+  seq->idx = idx;

+}

+

+/* Compare two sequences.  This version does not use the index and rules

+   cache.  */

+static int

+do_compare_nocache (coll_seq *seq1, coll_seq *seq2, int position,

+		    const USTRING_TYPE *weights)

+{

+  int seq1len = seq1->len;

+  int seq2len = seq2->len;

+  int val1 = seq1->val;

+  int val2 = seq2->val;

+  int idx1 = seq1->idx;

+  int idx2 = seq2->idx;

+  int result = 0;

+

+  /* Test for position if necessary.  */

+  if (position && val1 != val2)

+    {

+      result = val1 - val2;

+      goto out;

+    }

+

+  /* Compare the two sequences.  */

+  do

+    {

+      if (weights[idx1] != weights[idx2])

+	{

+	  /* The sequences differ.  */

+	  result = weights[idx1] - weights[idx2];

+	  goto out;

+	}

+

+      /* Increment the offsets.  */

+      ++idx1;

+      ++idx2;

+

+      --seq1len;

+      --seq2len;

+    }

+  while (seq1len > 0 && seq2len > 0);

+

+  if (position && seq1len != seq2len)

+    result = seq1len - seq2len;

+

+out:

+  seq1->len = seq1len;

+  seq2->len = seq2len;

+  seq1->idx = idx1;

+  seq2->idx = idx2;

+  return result;

+}

+

+/* Compare two sequences using the index cache.  */

 static int

 do_compare (coll_seq *seq1, coll_seq *seq2, int position,

 	    const USTRING_TYPE *weights)

@@ -334,57 +524,62 @@ STRCOLL (const STRING_TYPE *s1, const STRING_TYPE *s2, __locale_t l)

   memset (&seq1, 0, sizeof (seq1));

   seq2 = seq1;

-  /* We need the elements of the strings as unsigned values since they

-     are used as indeces.  */

-  seq1.us = (const USTRING_TYPE *) s1;

-  seq2.us = (const USTRING_TYPE *) s2;

-

   if (! __libc_use_alloca ((s1len + s2len) * (sizeof (int32_t) + 1)))

     {

       seq1.idxarr = (int32_t *) malloc ((s1len + s2len) * (sizeof (int32_t) + 1));

-      seq2.idxarr = &seq1.idxarr[s1len];

-      seq1.rulearr = (unsigned char *) &seq2.idxarr[s2len];

-      seq2.rulearr = &seq1.rulearr[s1len];

-

-      if (seq1.idxarr == NULL)

-	/* No memory.  Well, go with the stack then.

-

-	   XXX Once this implementation is stable we will handle this

-	   differently.  Instead of precomputing the indeces we will

-	   do this in time.  This means, though, that this happens for

-	   every pass again.  */

-	goto try_stack;

-      use_malloc = true;

+

+      /* If we failed to allocate memory, we leave everything as NULL so that

+	 we use the nocache version of traversal and comparison functions.  */

+      if (seq1.idxarr != NULL)

+	{

+	  seq2.idxarr = &seq1.idxarr[s1len];

+	  seq1.rulearr = (unsigned char *) &seq2.idxarr[s2len];

+	  seq2.rulearr = &seq1.rulearr[s1len];

+	  use_malloc = true;

+	}

     }

   else

     {

-    try_stack:

       seq1.idxarr = (int32_t *) alloca (s1len * sizeof (int32_t));

       seq2.idxarr = (int32_t *) alloca (s2len * sizeof (int32_t));

       seq1.rulearr = (unsigned char *) alloca (s1len);

       seq2.rulearr = (unsigned char *) alloca (s2len);

     }

-  seq1.rulearr[0] = 0;

+  int rule = 0;

   /* Cache values in the first pass and if needed, use them in subsequent

      passes.  */

   for (int pass = 0; pass < nrules; ++pass)

     {

       seq1.idxcnt = 0;

+      seq1.idx = 0;

+      seq2.idx = 0;

       seq1.backw_stop = ~0ul;

       seq1.backw = ~0ul;

       seq2.idxcnt = 0;

       seq2.backw_stop = ~0ul;

       seq2.backw = ~0ul;

+      /* We need the elements of the strings as unsigned values since they

+	 are used as indeces.  */

+      seq1.us = (const USTRING_TYPE *) s1;

+      seq2.us = (const USTRING_TYPE *) s2;

+

       /* We assume that if a rule has defined `position' in one section

 	 this is true for all of them.  */

-      int position = rulesets[seq1.rulearr[0] * nrules + pass] & sort_position;

+      int position = rulesets[rule * nrules + pass] & sort_position;

       while (1)

 	{

-	  if (pass == 0)

+	  if (__glibc_unlikely (seq1.idxarr == NULL))

+	    {

+	      get_next_seq_nocache (&seq1, nrules, rulesets, weights, table,

+				    extra, indirect, pass);

+	      get_next_seq_nocache (&seq2, nrules, rulesets, weights, table,

+				    extra, indirect, pass);

+	    }

+	  else if (pass == 0)

 	    {

 	      get_next_seq (&seq1, nrules, rulesets, weights, table, extra,

 			    indirect);

@@ -411,10 +606,18 @@ STRCOLL (const STRING_TYPE *s1, const STRING_TYPE *s2, __locale_t l)

 	      goto free_and_return;

 	    }

-	  result = do_compare (&seq1, &seq2, position, weights);

+	  if (__glibc_unlikely (seq1.idxarr == NULL))

+	    result = do_compare_nocache (&seq1, &seq2, position, weights);

+	  else

+	    result = do_compare (&seq1, &seq2, position, weights);

 	  if (result != 0)

 	    goto free_and_return;

 	}

+

+      if (__glibc_likely (seq1.rulearr != NULL))

+	rule = seq1.rulearr[0];

+      else

+	rule = seq1.rule;

     }

   /* Free the memory if needed.  */