On Tue, 11 Nov 2025 14:11:28 GMT, Harald Eilertsen <[email protected]> wrote:
> `jdk.internal.foreign.SegmentFactories::allocateNativeInternal` assumes that > the underlying implementation of malloc aligns allocations on 16 byte > boundaries for 64 bit platforms, and 8 byte boundaries on 32 bit platforms. > So for any allocation where the requested alignment is less than or equal to > this default alignment it makes no adjustment. > > However, this assumption does not hold for all allocators. Specifically > jemallc, used by libc on FreeBSD will align small allocations on 8 or 4 byte > boundaries, respectively. This causes allocateNativeInternal to sometimes > return memory that is not properly aligned when the requested alignment is > exactly 16 bytes. > > To make sure we honour the requested alignment when it exaclty matches the > quantum as defined by MAX_MALLOC_ALIGN, this patch ensures that we adjust the > alignment also in this case. > > This should make no difference for platforms where malloc allready aligns on > the quantum, except for a few unnecessary trivial calculations. > > This work was sponsored by: The FreeBSD Foundation Are you saying that jemalloc aligns allocations that are _exactly_ 16 bytes on an 8 byte boundary? How does this work when you want to allocate space for a single 16-byte size, 16-byte aligned value? (e.g. long double? I think FreeBSD uses the SysV ABI, right?) ------------- PR Comment: https://git.openjdk.org/jdk/pull/28235#issuecomment-3517472567
