[Bug 232176] elftoolchain elfcopy/strip incorrectly strips relocations

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=232176

--- Comment #6 from commit-hook at freebsd.org ---
A commit references this bug:

Author: emaste
Date: Thu Oct 25 13:46:28 UTC 2018
New revision: 339710
URL: https://svnweb.freebsd.org/changeset/base/339710

Log:
  elfcopy: avoid stripping relocations from static binaries

  MFC r339350: elfcopy: delete filter_reloc, it is broken and unnecessary

  elfcopy contained logic to filter individual relocations in STRIP_ALL
  mode.  However, this is not valid; relocations emitted by the linker are
  required, unless they apply to an entire section being removed (which is
  handled by other logic in elfcopy).

  Note that filter_reloc was also buggy: for RELA relocation sections it
  operated on uninitialized rel.r_info resulting in invalid operation.

  The logic most likely needs to be inverted: instead of removing
  relocations because their associated symbols are being removed, we must
  keep symbols referenced by relocations.  That said, in practice we do
  not encounter this code path today: objects being stripped are either
  dynamically linked binaries which retain .dynsym, or static binaries
  with no relocations.

  Just remove filter_reloc.  This fixes certain cases including statically
  linked binaries containing ifuncs.  Stripping binaries with relocations
  referencing removed symbols was already broken, and after this change
  may still be broken in a different way.

  MFC r339451: objcopy: restore behaviour required by GCC's build

  In r339350 filter_reloc() was removed, to fix the case of stripping
  statically linked binaries with relocations (which may come from ifunc
  use, for example).  As a side effect this changed the behaviour when
  stripping object files - the output was broken both before and after
  r339350, in different ways.  Unfortunately GCC's build process relies
  on the previous behaviour, so:

  - Revert r339350, restoring filter_reloc().
  - Fix an unitialized variable use (commited as r3638 in ELF Tool Chain).
  - Change filter_reloc() to omit relocations referencing removed
    symbols, while retaining relocations with no symbol reference.
  - Retain the entire relocation section if it references the dynamic
    symbol table (fix from kaiw in D17596).

  PR:           232176
  Sponsored by: The FreeBSD Foundation

Changes:
_U  stable/11/
  stable/11/contrib/elftoolchain/elfcopy/sections.c

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