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. */