mozilla/rust — comment on commit 1c7a62c93b21ad1958db80b39bca14a09ea8b4bc
File: src/rt/rust_upcall.cpp line 236
By nikomatsakis:

I don't think the use of align_to() here makes sense. The alignment affects on what boundary ptr will be aligned, not the size. If `align` represented the alignment of the next field in the structure, then this would have the effect of zeroing out the padding as well as the structure in `ptr`, but that doesn't seem necessary to do.