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LibWasm: Fix UB in LibWasm

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Now that `Optional<T&>` are trivially copyable/movable, it is
triggering Undefined Behaviour checks on GCC. We can resolve those
by using an union.
This commit is contained in:
Jonne Ransijn 2024-11-28 12:13:01 +01:00 • committed by Ali Mohammad Pur
parent 55383998b1
commit d7a721951e
Notes: github-actions[bot] 2024-12-04 00:59:38 +00:00
1 changed files with 18 additions and 15 deletions
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33
Libraries/LibWasm/Wasi.h
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@ -738,30 +738,31 @@ static_assert(sizeof(SockRecvResult) == 8);
template<typename TResult, typename Tag = u32>
struct Result {
Result(TResult&& result)
: bits {}
: m_result(result)
, tag(0)
{
new (&bits) TResult(move(result));
}
Result(Errno&& error)
: bits {}
: m_error(error)
, tag(1)
{
new (&bits) Errno(error);
}
Optional<TResult&> result() const
static_assert(IsTriviallyDestructible<TResult>);
static_assert(IsTriviallyDestructible<Errno>);
Optional<TResult const&> result() const
{
if (tag == 0)
return *bit_cast<TResult*>(&bits[0]);
return m_result;
return {};
}
Optional<Errno&> error() const
Optional<Errno const&> error() const
{
if (tag == 1)
return *bit_cast<Errno*>(&bits[0]);
return m_error;
return {};
}
@ -778,23 +779,25 @@ struct Result {
}
private:
alignas(max(alignof(TResult), alignof(Errno))) u8 bits[max(sizeof(TResult), sizeof(Errno))];
union {
TResult m_result;
Errno m_error;
};
LittleEndian<Tag> tag;
};
template<typename Tag>
struct Result<void, Tag> {
Result()
: error_bits {}
: m_error()
, tag(0)
{
}
Result(Errno&& error)
: error_bits {}
: m_error(error)
, tag(1)
{
new (&error_bits) Errno(error);
}
Optional<Empty> result() const
@ -803,16 +806,16 @@ struct Result<void, Tag> {
return { Empty {} };
return {};
}
Optional<Errno&> error() const
Optional<Errno const&> error() const
{
if (tag == 1)
return *bit_cast<Errno*>(&error_bits[0]);
return m_error;
return {};
}
bool is_error() const { return tag == 1; }
private:
alignas(Errno) u8 error_bits[sizeof(Errno)];
Errno m_error;
LittleEndian<Tag> tag;
};