Help to figure out meaning of assert

[Vanegicloh J]

Hello. I'm trying to use arena in protobuf with C++ but keep getting weird assertion fail. I create std::array<char, 1024> on the stack and pass it to the arena as the initial block like this:

google::protobuf::Arena m_arena{arenaBuf.data(), arenaBuf.size()}.

During arena construction i get "CHECK failed: (reinterpret_cast<uintptr_t>(mem) & 7) == (0u)". Could you please help me to figure out what does it mean? What should i do to fix it?

P.s. it's very weird because only in 1 test file this assert fails. I do the same everywhere in the project, but only 1 test doesn't want to run and fails with this assert.

Also, we got some old protobuf code. Not one that in github master. The function with weird assert is this:

void ThreadSafeArena::InitializeFrom(void* mem, size_t size)

{

GOOGLE_DCHECK_EQ(reinterpret_cast<uintptr_t>(mem) & 7, 0u);

GOOGLE_DCHECK(!AllocPolicy());

// Reset should call InitializeWithPolicy instead. Init();

// Ignore initial block if it is too small.

if (mem != nullptr && size >= kBlockHeaderSize + kSerialArenaSize) 

{ 

alloc_policy_.set_is_user_owned_initial_block(true); SetInitialBlock(mem, size); 

}

}

[Samuel Benzaquen]

On Thu, Apr 3, 2025 at 10:44 AM Vanegicloh J <vaneg...@gmail.com> wrote:

Hello. I'm trying to use arena in protobuf with C++ but keep getting weird assertion fail. I create std::array<char, 1024> on the stack and pass it to the arena as the initial block like this:

google::protobuf::Arena m_arena{arenaBuf.data(), arenaBuf.size()}.

During arena construction i get "CHECK failed: (reinterpret_cast<uintptr_t>(mem) & 7) == (0u)". Could you please help me to figure out what does it mean? What should i do to fix it?

The buffer is not properly aligned.

The arena requires the provided input buffer to be at least 8-byte aligned.

You can solve this by declaring your variable with `alignas(8)`, or use a type that is already aligned.

 

P.s. it's very weird because only in 1 test file this assert fails. I do the same everywhere in the project, but only 1 test doesn't want to run and fails with this assert.

Also, we got some old protobuf code. Not one that in github master. The function with weird assert is this:

void ThreadSafeArena::InitializeFrom(void* mem, size_t size)

{

GOOGLE_DCHECK_EQ(reinterpret_cast<uintptr_t>(mem) & 7, 0u);

GOOGLE_DCHECK(!AllocPolicy());

// Reset should call InitializeWithPolicy instead. Init();

// Ignore initial block if it is too small.

if (mem != nullptr && size >= kBlockHeaderSize + kSerialArenaSize) 

{ 

alloc_policy_.set_is_user_owned_initial_block(true); SetInitialBlock(mem, size); 

}

}

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