[lld-macho] Ensure __bss sections we output have file offset of zero
Summary:
llvm-mc emits `__bss` sections with an offset of zero, but we weren't expecting
that in our input, so we were copying non-zero data from the start of the file and
putting it in `__bss`, with obviously undesirable runtime results. (It appears that
the kernel will copy those nonzero bytes as long as the offset is nonzero, regardless
of whether S_ZERO_FILL is set.)
I debated on whether to make a special ZeroFillSection -- separate from a
regular InputSection -- but it seemed like too much work for now. But I'm happy
to refactor if anyone feels strongly about having it as a separate class.
Depends on D80857.
Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee
Reviewed By: smeenai
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D80859