diff options
| -rw-r--r-- | src/corelib/global/qrandom.cpp | 29 |
1 files changed, 26 insertions, 3 deletions
diff --git a/src/corelib/global/qrandom.cpp b/src/corelib/global/qrandom.cpp index eb9eaa68de..0601dbdb30 100644 --- a/src/corelib/global/qrandom.cpp +++ b/src/corelib/global/qrandom.cpp @@ -52,6 +52,10 @@ # include "qhashfunctions.h" #endif +#if QT_HAS_INCLUDE(<sys/auxv.h>) +# include <sys/auxv.h> +#endif + #ifdef Q_OS_UNIX # include <fcntl.h> # include <private/qcore_unix_p.h> @@ -247,12 +251,31 @@ static void fallback_fill(quint32 *ptr, qssize_t left) Q_DECL_NOTHROW { Q_ASSERT(left); + // ELF's auxv AT_RANDOM has 16 random bytes + using RandomBytes = quint32[16 / sizeof(quint32)]; + RandomBytes scratch = {}; + RandomBytes *auxvSeed = nullptr; + +#if QT_HAS_INCLUDE(<sys/auxv.h>) && defined(AT_RANDOM) + // works on Linux -- all modern libc have getauxval + // other ELF-based systems don't seem to have AT_RANDOM + auxvSeed = reinterpret_cast<RandomBytes *>(getauxval(AT_RANDOM)); + if (auxvSeed) + memcpy(scratch, auxvSeed, sizeof(RandomBytes)); +#endif + quint32 v = seed.load(); - if (Q_UNLIKELY(v == 0)) - emergency_seed(v); + if (Q_LIKELY(v)) { + // mix the stored seed value + // (using the fact that qHash(unsigned) is idempotent) + scratch[0] = QtPrivate::QHashCombine()(scratch[0], v); + } else if (Q_UNLIKELY(auxvSeed == nullptr)) { + emergency_seed(scratch[0]); + } // this is highly inefficient, we should save the generator across calls... - std::mt19937 generator(v); + std::seed_seq sseq(std::begin(scratch), std::end(scratch)); + std::mt19937 generator(sseq); std::generate(ptr, ptr + left, generator); fallback_update_seed(*ptr); |