shufti-double: fix regressions from #325 (#368)

* shufti-double: Fix double shufti's caller

run_accel() passed c_end - 1 to shuftiDoubleExec().
shuftiDoubleExecReal already handles the last-byte boundary internally
via check_last_byte(), so shortening the buffer caused it to miss
valid matches near the end and apply the wildcard check to the wrong
byte. Changed to pass c_end.

Fixes: ca70a3d9beca61b58c6709fead60ec662482d36e ("Fix double shufti's
vector end false positive (#325)")

Signed-off-by: Byeonguk Jeong <jungbu2855@gmail.com>
* shufti-double: Preserve first_char_mask after peel-off

first_char_mask was reset to Ones() after the peel-off block,
discarding carry-over state for cross-boundary pattern detection.
Remove the reset.

Fixes: ca70a3d9beca61b58c6709fead60ec662482d36e ("Fix double shufti's
vector end false positive (#325)")

Signed-off-by: Byeonguk Jeong <jungbu2855@gmail.com>
* shufti-double: Fix check_last_byte() loop condition

loop condition i > 2 missed the final vshr(1), leaving odd-indexed
bytes out of the reduce. Use i >= 2.

Fixes: ca70a3d9beca61b58c6709fead60ec662482d36e ("Fix double shufti's
vector end false positive (#325)")

Signed-off-by: Byeonguk Jeong <jungbu2855@gmail.com>
* shufti-double: Add regression tests for double shufti

Add three tests exercising the double shufti edge cases.

- ExecMatchVectorEdge: Two-byte pair ("ab") spanning the peel-off to
  aligned block boundary is correctly detected. Validates that
  first_char_mask state carries over and is not reset after peel-off.

- ExecNoMatchLastByte: First character of a double-byte pair ('x' from
  "xy") at the last buffer byte does not cause a false positive when
  the second character is absent.

- ExecMatchLastByte: Single-byte pattern ('a') at the last buffer byte
  is detected via check_last_byte's reduce.

Signed-off-by: Byeonguk Jeong <jungbu2855@gmail.com>
---------

Signed-off-by: Byeonguk Jeong <jungbu2855@gmail.com>

diff --git a/src/nfa/accel.c b/src/nfa/accel.c
index 027f1182bf69785dd1a45086c61c8fed6f01a520..b59d1c8c1c3b6fa46dca441457e3df671fdaf061 100644 (file)
--- a/src/nfa/accel.c
+++ b/src/nfa/accel.c
@@ -160,11 +160,12 @@ const u8 *run_accel(const union AccelAux *accel, const u8 *c, const u8 *c_end) {
             return c;
         }
 
-        /* need to stop one early to get an accurate end state */
+        /* Shufti double handles its own ending boundary checks internally
+         * to correctly identify matches at the last byte. */
         rv = shuftiDoubleExec(accel->dshufti.lo1,
                               accel->dshufti.hi1,
                               accel->dshufti.lo2,
-                              accel->dshufti.hi2, c, c_end - 1);
+                              accel->dshufti.hi2, c, c_end);
         break;
 
     case ACCEL_RED_TAPE:

diff --git a/src/nfa/shufti_simd.hpp b/src/nfa/shufti_simd.hpp
index c5989aa0f36644eb6f42e003de7f3cb9df08a835..9b3d5a29a382459aaab2bccd13db6202dc3c4029 100644 (file)
--- a/src/nfa/shufti_simd.hpp
+++ b/src/nfa/shufti_simd.hpp
@@ -208,7 +208,7 @@ const u8 *check_last_byte(SuperVector<S> mask2_lo, SuperVector<S> mask2_hi,
     uint8_t last_elem = mask.u.u8[mask_len - 1];
 
     SuperVector<S> reduce = mask2_lo | mask2_hi;
-    for(uint16_t i = S; i > 2; i/=2) {
+    for(uint16_t i = S; i >= 2; i/=2) {
         reduce = reduce | reduce.vshr(i/2);
     }
     uint8_t match_inverted = reduce.u.u8[0] | last_elem;
@@ -260,7 +260,6 @@ const u8 *shuftiDoubleExecReal(m128 mask1_lo, m128 mask1_hi, m128 mask2_lo, m128
             first_char_mask.print8("inout_c1 shifted");
         }
 
-        first_char_mask = SuperVector<S>::Ones();
         while(d + S <= buf_end) {
             __builtin_prefetch(d + 64);
             DEBUG_PRINTF("d %p \n", d);

diff --git a/unit/internal/shufti.cpp b/unit/internal/shufti.cpp
index d5f291d9e7707c4871980874d322d849f8782e6d..29e6f64f96fb529c414ac138483cd03137a23493 100644 (file)
--- a/unit/internal/shufti.cpp
+++ b/unit/internal/shufti.cpp
@@ -990,6 +990,94 @@ TEST(DoubleShufti, ExecNoOverreadPageBoundary) {
     munmap(pages, page_size);
 }
 
+TEST(DoubleShufti, ExecMatchVectorEdge) {
+    m128 lo1, hi1, lo2, hi2;
+
+    flat_set<pair<u8, u8>> lits;
+    lits.insert(make_pair('a', 'b'));
+
+    bool ret = shuftiBuildDoubleMasks(CharReach(), lits, reinterpret_cast<u8 *>(&lo1), reinterpret_cast<u8 *>(&hi1),
+                                      reinterpret_cast<u8 *>(&lo2), reinterpret_cast<u8 *>(&hi2));
+    ASSERT_TRUE(ret);
+
+    const int len = 80;
+    const int vector_size = 16;
+    for (size_t start = 1; start < vector_size; start++) {
+        char t[len];
+        memset(t, 'z', len);
+        char *buf = t + start;
+        int buf_len = len - start;
+
+        uintptr_t aligned = (reinterpret_cast<uintptr_t>(buf) + vector_size - 1) &
+                            ~static_cast<uintptr_t>(vector_size - 1);
+        ptrdiff_t boundary = reinterpret_cast<const char *>(aligned) - buf;
+
+        if (boundary < 1 || boundary >= buf_len - 1) continue;
+
+        buf[boundary - 1] = 'a';
+        buf[boundary] = 'b';
+
+        const u8 *rv = shuftiDoubleExec(lo1, hi1, lo2, hi2,
+                                        reinterpret_cast<u8 *>(buf),
+                                        reinterpret_cast<u8 *>(buf) + buf_len);
+
+        ASSERT_EQ(reinterpret_cast<const u8 *>(buf + boundary - 1), rv)
+            << "Failed for start=" << start << " boundary=" << boundary;
+    }
+}
+
+TEST(DoubleShufti, ExecNoMatchLastByte) {
+    m128 lo1, hi1, lo2, hi2;
+
+    flat_set<pair<u8, u8>> lits;
+    lits.insert(make_pair('x', 'y'));
+
+    bool ret = shuftiBuildDoubleMasks(CharReach(), lits, reinterpret_cast<u8 *>(&lo1), reinterpret_cast<u8 *>(&hi1),
+                                      reinterpret_cast<u8 *>(&lo2), reinterpret_cast<u8 *>(&hi2));
+    ASSERT_TRUE(ret);
+
+    const int maxlen = 80;
+    char t1[maxlen + 1];
+    for (int len = 17; len < maxlen; len++) {
+        memset(t1, 'b', len + 1);
+        t1[len - 1] = 'x';
+
+        const u8 *rv = shuftiDoubleExec(lo1, hi1, lo2, hi2,
+                                        reinterpret_cast<u8 *>(t1),
+                                        reinterpret_cast<u8 *>(t1) + len);
+
+        ASSERT_EQ(reinterpret_cast<const u8 *>(t1 + len), rv)
+            << "Failed for len=" << len;
+    }
+}
+
+TEST(DoubleShufti, ExecMatchLastByte) {
+    m128 lo1, hi1, lo2, hi2;
+
+    CharReach onebyte;
+    flat_set<pair<u8, u8>> twobyte;
+
+    onebyte.set('a');
+    twobyte.insert(make_pair('x', 'y'));
+
+    bool ret = shuftiBuildDoubleMasks(onebyte, twobyte, reinterpret_cast<u8 *>(&lo1), reinterpret_cast<u8 *>(&hi1),
+                                      reinterpret_cast<u8 *>(&lo2), reinterpret_cast<u8 *>(&hi2));
+    ASSERT_TRUE(ret);
+
+    const int maxlen = 80;
+    char t1[maxlen + 1];
+    for (int len = 17; len < maxlen; len++) {
+        memset(t1, 'b', len + 1);
+        t1[len - 1] = 'a';
+
+        const u8 *rv = shuftiDoubleExec(lo1, hi1, lo2, hi2,
+                                        reinterpret_cast<u8 *>(t1),
+                                        reinterpret_cast<u8 *>(t1) + len);
+
+        ASSERT_EQ(reinterpret_cast<const u8 *>(t1 + len - 1), rv);
+    }
+}
+
 TEST(ReverseShufti, ExecNoMatch1) {
     m128 lo, hi;