PR28827 - [2.38 Regression] ld hits assertion building LLVM 9 on powerpc64le-linux-gnu

[Alan Modra]

Hi Nick, HJ,
I've spent most of today debugging a build of libclang-cpp.so.9 using
the binutils 2.38 release branch.  The problem occurs after only a few
iterations of stub sizing, so all the patches I already committed for
potential bugs when we hit 20 iteration don't so anything as far as
actually linking the real object files.

The problem is caused by the new relro code introducing a gap at the
end of the relro segment.  On powerpc64 that means between the .got
and .plt section.  That gap changes when .eh_frame shrinks after
consolidating CIEs and garbage collecting unused FDEs, which happens
after the stub sizing passes are run from ldemul_after_allocation.
Unfortunately, if the .got/.plt gap increases, plt call stubs may need
to be larger to access addresses in the PLT from the toc pointer reg
and thus not fit in space allocated for them.

Please revert the relro patches on the branch.  I'm now certain that
PR28827 is directly caused by them.

-- 
Alan Modra
Australia Development Lab, IBM