[PATCH] D100848: [lld-macho] Ensure segments are laid out contiguously

[Jez Ng via Phabricator via llvm-commits]

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codesign/libstuff checks that the `__LLVM` segment is directly
before `__LINKEDIT` by checking that `fileOff + fileSize == next segment
fileOff`. Previously, there would be gaps between the segments due to
the fact that their fileOffs are page-aligned but their fileSizes
aren't. In order to satisfy codesign, we page-align fileOff *before*
calculating fileSize. (I don't think codesign checks for the relative
ordering of other segments, so in theory we could do this just for
`__LLVM`, but ld64 seems to do it for all segments.)

Note that we *don't* round up the fileSize of the `__LINKEDIT` segment.
Since it's the last segment, so it doesn't need to worry about
contiguity; in addition, codesign checks that the last (hidden) section
in `__LINKEDIT` covers the last byte of the segment, so if we rounded up
`__LINKEDIT`'s size we would have to do the same for its last section,
which is a bother.

While at it, I also addressed a FIXME in the linkedit-contiguity.s test
to cover more `__LINKEDIT` sections.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D100848

Files:
  lld/MachO/OutputSegment.h
  lld/MachO/Writer.cpp
  lld/test/MachO/bitcode-bundle.ll
  lld/test/MachO/bss.s
  lld/test/MachO/linkedit-contiguity.s
  lld/test/MachO/section-headers.s
  lld/test/MachO/segments.s

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