diff options
| -rw-r--r-- | src/corelib/tools/qhash.cpp | 32 | ||||
| -rw-r--r-- | tests/auto/corelib/tools/qhashfunctions/tst_qhashfunctions.cpp | 8 |
2 files changed, 27 insertions, 13 deletions
diff --git a/src/corelib/tools/qhash.cpp b/src/corelib/tools/qhash.cpp index 662c304a2e..09f3fd8e83 100644 --- a/src/corelib/tools/qhash.cpp +++ b/src/corelib/tools/qhash.cpp @@ -203,7 +203,7 @@ static inline uint hash(const uchar *p, size_t len, uint seed) Q_DECL_NOTHROW { uint h = seed; - if (hasFastCrc32()) + if (seed && hasFastCrc32()) return crc32(p, len, h); for (size_t i = 0; i < len; ++i) @@ -221,7 +221,7 @@ static inline uint hash(const QChar *p, size_t len, uint seed) Q_DECL_NOTHROW { uint h = seed; - if (hasFastCrc32()) + if (seed && hasFastCrc32()) return crc32(p, len, h); for (size_t i = 0; i < len; ++i) @@ -288,8 +288,15 @@ static uint qt_create_qhash_seed() #ifndef QT_BOOTSTRAPPED QByteArray envSeed = qgetenv("QT_HASH_SEED"); - if (!envSeed.isNull()) - return envSeed.toUInt(); + if (!envSeed.isNull()) { + uint seed = envSeed.toUInt(); + if (seed) { + // can't use qWarning here (reentrancy) + fprintf(stderr, "QT_HASH_SEED: forced seed value is not 0, cannot guarantee that the " + "hashing functions will produce a stable value."); + } + return seed; + } #ifdef Q_OS_UNIX int randomfd = qt_safe_open("/dev/urandom", O_RDONLY); @@ -379,14 +386,17 @@ int qGlobalQHashSeed() is needed. We discourage to do it in production code as it can make your application susceptible to \l{algorithmic complexity attacks}. + From Qt 5.10 and onwards, the only allowed values are 0 and -1. Passing the + value -1 will reinitialize the global QHash seed to a random value, while + the value of 0 is used to request a stable algorithm for C++ primitive + types types (like \c int) and string types (QString, QByteArray). + The seed is set in any newly created QHash. See \l{qHash} about how this seed is being used by QHash. If the environment variable \c QT_HASH_SEED is set, calling this function will result in a no-op. - Passing the value -1 will reinitialize the global QHash seed to a random value. - \sa qGlobalQHashSeed */ void qSetGlobalQHashSeed(int newSeed) @@ -397,6 +407,11 @@ void qSetGlobalQHashSeed(int newSeed) int x(qt_create_qhash_seed() & INT_MAX); qt_qhash_seed.store(x); } else { + if (newSeed) { + // can't use qWarning here (reentrancy) + fprintf(stderr, "qSetGlobalQHashSeed: forced seed value is not 0, cannot guarantee that the " + "hashing functions will produce a stable value."); + } qt_qhash_seed.store(newSeed & INT_MAX); } } @@ -1254,9 +1269,8 @@ uint qHash(long double key, uint seed) Q_DECL_NOTHROW should never depend on a particular QHash ordering, there may be situations where you temporarily need deterministic behavior, for example for debugging or regression testing. To disable the randomization, define the environment - variable \c QT_HASH_SEED. The contents of that variable, interpreted as a - decimal value, will be used as the seed for qHash(). Alternatively, you can - call the qSetGlobalQHashSeed() function. + variable \c QT_HASH_SEED to have the value 0. Alternatively, you can call + the qSetGlobalQHashSeed() function with the value 0. \sa QHashIterator, QMutableHashIterator, QMap, QSet */ diff --git a/tests/auto/corelib/tools/qhashfunctions/tst_qhashfunctions.cpp b/tests/auto/corelib/tools/qhashfunctions/tst_qhashfunctions.cpp index dbfcf57955..124e3cdf00 100644 --- a/tests/auto/corelib/tools/qhashfunctions/tst_qhashfunctions.cpp +++ b/tests/auto/corelib/tools/qhashfunctions/tst_qhashfunctions.cpp @@ -284,17 +284,17 @@ void tst_QHashFunctions::rangeCommutative() void tst_QHashFunctions::setGlobalQHashSeed() { // Setter works as advertised - qSetGlobalQHashSeed(0x10101010); - QCOMPARE(qGlobalQHashSeed(), 0x10101010); + qSetGlobalQHashSeed(0); + QCOMPARE(qGlobalQHashSeed(), 0); // Creating a new QHash doesn't reset the seed QHash<QString, int> someHash; someHash.insert("foo", 42); - QCOMPARE(qGlobalQHashSeed(), 0x10101010); + QCOMPARE(qGlobalQHashSeed(), 0); // Reset works as advertised qSetGlobalQHashSeed(-1); - QVERIFY(qGlobalQHashSeed() != -1); + QVERIFY(qGlobalQHashSeed() > 0); } QTEST_APPLESS_MAIN(tst_QHashFunctions) |