[PATCH] D19844: ELF: Forbid all relative relocations to absolute symbols in PIC, except for weak undefined.

[Peter Collingbourne via llvm-commits]

pcc created this revision.
pcc added reviewers: rafael, ruiu.
pcc added a subscriber: llvm-commits.

Weak undefined symbols resolve to the image base. This is a little strange,
but it allows us to link function calls to such symbols. Normally such a
call will be guarded with a comparison, which will load a zero from the GOT.

There's one example of such a function call in crti.o in Linux's CRT.

As part of this change, I also needed to make the synthetic start and end
symbols image base relative in the case where their sections were empty,
so that PC-relative references to those symbols would continue to work.

http://reviews.llvm.org/D19844

Files:
  ELF/OutputSections.cpp
  ELF/SymbolTable.cpp
  ELF/SymbolTable.h
  ELF/Symbols.cpp
  ELF/Symbols.h
  ELF/Writer.cpp
  test/ELF/relocation-relative-absolute.s
  test/ELF/relocation-relative-synthetic.s
  test/ELF/relocation-relative-weak.s

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