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AK: Add an option to zero-fill ByteBuffer data upon growth

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This is to avoid UB in cases where we need to be able to read from the
buffer immediately after resizing it.
This commit is contained in:
Timothy Flynn 2023-12-27 10:11:20 -05:00 • committed by Andreas Kling
parent 759c8ccc55
commit 507a5d8a07
2 changed files with 30 additions and 3 deletions
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16
AK/ByteBuffer.h
View file

@ -163,9 +163,14 @@ public:
m_size = 0;
}
ALWAYS_INLINE void resize(size_t new_size)
enum class ZeroFillNewElements {
No,
Yes,
};
ALWAYS_INLINE void resize(size_t new_size, ZeroFillNewElements zero_fill_new_elements = ZeroFillNewElements::No)
{
MUST(try_resize(new_size));
MUST(try_resize(new_size, zero_fill_new_elements));
}
void trim(size_t size, bool may_discard_existing_data)
@ -181,13 +186,18 @@ public:
MUST(try_ensure_capacity(new_capacity));
}
ErrorOr<void> try_resize(size_t new_size)
ErrorOr<void> try_resize(size_t new_size, ZeroFillNewElements zero_fill_new_elements = ZeroFillNewElements::No)
{
if (new_size <= m_size) {
trim(new_size, false);
return {};
}
TRY(try_ensure_capacity(new_size));
if (zero_fill_new_elements == ZeroFillNewElements::Yes) {
__builtin_memset(data() + m_size, 0, new_size - m_size);
}
m_size = new_size;
return {};
}

17
Tests/AK/TestByteBuffer.cpp
View file

@ -46,6 +46,23 @@ TEST_CASE(byte_buffer_vector_contains_slow_bytes)
EXPECT_EQ(vector.contains_slow(c), true);
}
TEST_CASE(zero_fill_new_elements_on_growth)
{
auto buffer = MUST(ByteBuffer::create_uninitialized(5));
buffer.span().fill(1);
EXPECT_EQ(buffer.span(), (Array<u8, 5> { 1, 1, 1, 1, 1 }));
buffer.resize(8, ByteBuffer::ZeroFillNewElements::Yes);
EXPECT_EQ(buffer.span(), (Array<u8, 8> { 1, 1, 1, 1, 1, 0, 0, 0 }));
buffer.span().fill(2);
EXPECT_EQ(buffer.span(), (Array<u8, 8> { 2, 2, 2, 2, 2, 2, 2, 2 }));
buffer.resize(10, ByteBuffer::ZeroFillNewElements::Yes);
EXPECT_EQ(buffer.span(), (Array<u8, 10> { 2, 2, 2, 2, 2, 2, 2, 2, 0, 0 }));
}
BENCHMARK_CASE(append)
{
ByteBuffer bb;