diff options
author | Andrei Golubev <andrei.golubev@qt.io> | 2021-01-22 09:26:09 +0100 |
---|---|---|
committer | Qt Cherry-pick Bot <cherrypick_bot@qt-project.org> | 2021-01-26 16:27:37 +0000 |
commit | a6c6d0bb8964f8860f53973410c70e00ac373201 (patch) | |
tree | 651a22dca251582700c7683703ee311e29681110 /src | |
parent | 3947279d68859a445a3f723e31cef9aa1104be3d (diff) |
Extend alignment of QArrayData to std::max_align_t in allocation
Make stricter alignment requirements for the allocated header
This strict alignment allows reallocateUnaligned() to property account
for the padding occurring in cases when
alignof(QArrayData) < alignof(T) <= alignof(std::max_align_t), which
happens to be the case on e.g. 32-bit platforms with specific alignment
requirements.
This adds 4 bytes (the difference between alignof(std::max_align_t) and
sizeof(QArrayData)) of overhead for QString, QByteArray and certain QLists
on 32-bit systems.
Task-number: QTBUG-90359
Change-Id: I8176a4cc79f100ee772b09425e88fe8ff3ae226a
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
(cherry picked from commit 37e26d2b3011acc86bbda1e1f46114d7c8441915)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
Diffstat (limited to 'src')
-rw-r--r-- | src/corelib/tools/qarraydata.cpp | 23 |
1 files changed, 16 insertions, 7 deletions
diff --git a/src/corelib/tools/qarraydata.cpp b/src/corelib/tools/qarraydata.cpp index 8ca315024d..3297b51cfe 100644 --- a/src/corelib/tools/qarraydata.cpp +++ b/src/corelib/tools/qarraydata.cpp @@ -1,6 +1,6 @@ /**************************************************************************** ** -** Copyright (C) 2020 The Qt Company Ltd. +** Copyright (C) 2021 The Qt Company Ltd. ** Copyright (C) 2016 Intel Corporation. ** Contact: https://www.qt.io/licensing/ ** @@ -184,6 +184,15 @@ static QArrayData *allocateData(qsizetype allocSize) return header; } + +namespace { +// QArrayData with strictest alignment requirements supported by malloc() +struct alignas(std::max_align_t) AlignedQArrayData : QArrayData +{ +}; +} + + void *QArrayData::allocate(QArrayData **dptr, qsizetype objectSize, qsizetype alignment, qsizetype capacity, QArrayData::AllocationOption option) noexcept { @@ -197,13 +206,13 @@ void *QArrayData::allocate(QArrayData **dptr, qsizetype objectSize, qsizetype al return nullptr; } - qsizetype headerSize = sizeof(QArrayData); - const qsizetype headerAlignment = alignof(QArrayData); + qsizetype headerSize = sizeof(AlignedQArrayData); + const qsizetype headerAlignment = alignof(AlignedQArrayData); if (alignment > headerAlignment) { - // Allocate extra (alignment - Q_ALIGNOF(QArrayData)) padding bytes so we - // can properly align the data array. This assumes malloc is able to - // provide appropriate alignment for the header -- as it should! + // Allocate extra (alignment - Q_ALIGNOF(AlignedQArrayData)) padding + // bytes so we can properly align the data array. This assumes malloc is + // able to provide appropriate alignment for the header -- as it should! headerSize += alignment - headerAlignment; } Q_ASSERT(headerSize > 0); @@ -233,7 +242,7 @@ QArrayData::reallocateUnaligned(QArrayData *data, void *dataPointer, { Q_ASSERT(!data || !data->isShared()); - const qsizetype headerSize = sizeof(QArrayData); + const qsizetype headerSize = sizeof(AlignedQArrayData); qsizetype allocSize = calculateBlockSize(capacity, objectSize, headerSize, option); if (Q_UNLIKELY(allocSize < 0)) return qMakePair<QArrayData *, void *>(nullptr, nullptr); |