[Bug ld/21181] All executables segfault when linked with -z,now on Alpha.

[amodra at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=21181

Alan Modra <amodra at gmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2017-02-20
                 CC|                            |amodra at gmail dot com
           Assignee|unassigned at sourceware dot org   |amodra at gmail dot com
     Ever confirmed|0                           |1

--- Comment #1 from Alan Modra <amodra at gmail dot com> ---
I think this was very likely triggered by my elf_backend_dtrel_excludes_plt
change, git commit 64f52338e9.  Architectures other than alpha are likely to be
affected too, if you can manage to create a binary with plt dynamic relocs but
no other dynamic relocs, and DT_RELA/DT_RELASZ are emitted.

I'm guessing that all the bad -z now binaries have DT_RELASZ zero, which would
mean that the value of DT_RELA should not matter.  Except that it does, due to
a glibc bug.  See glibc/elf/dynamic_link.h _ELF_DYNAMIC_DO_RELOC and note what
happens during processing of DT_PLTREL with DT_RELA/DT_RELASIZ as you describe.
 No PLT reloc processing for you!

It's also a bug that alpha ld emits DT_RELA/DT_RELASZ when DT_RELASZ is zero.

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