V8 10.8: Static asserts on Windows x86 build

[ClearScript Developers]

Folks,

We're hitting the following in Windows x86 builds of 10.8:

./../..\src/heap/spaces.h(344,35): note: expression evaluates to '152 <= 148'
static_assert(sizeof(MemoryChunk) <= MemoryChunk::kHeaderSize);

Anyone else?

[dinf...@chromium.org]

Hi,

We recently looked into such an issue. This was caused by std::bitset (used by MemoryChunk::active_system_pages_) having different sizes in clang vs msvc. Are you using msvc by chance?

Cheers,

Dominik

[ClearScript Developers]

Hi Dominik,

Thanks for your reply. Here's our GN config:

enable_precompiled_headers = false
fatal_linker_warnings = false
is_component_build = false
is_debug = false
target_cpu = "x86"
use_custom_libcxx = false
use_thin_lto = false
v8_enable_pointer_compression = false
v8_enable_31bit_smis_on_64bit_arch = false
v8_monolithic = true
v8_target_cpu = "x86"
v8_use_external_startup_data = false

Thanks!

[ClearScript Developers]

We added the following:

static_assert(offsetof(MemoryChunk, was_used_for_allocation_) == MemoryChunkLayout::kWasUsedForAllocationOffset);
static_assert(sizeof(MemoryChunk) == MemoryChunkLayout::kWasUsedForAllocationOffset + sizeof(size_t));

The second assert fails, as if MemoryChunk had an extra field or was padded out to an 8-byte boundary. Probably the latter?