[Bug binutils/23919] New: bfd doesn't handle ELF compressed data alignment

mark at klomp dot org sourceware-bugzilla@sourceware.org
Sat Nov 24 22:09:00 GMT 2018


            Bug ID: 23919
           Summary: bfd doesn't handle ELF compressed data alignment
           Product: binutils
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: binutils
          Assignee: unassigned at sourceware dot org
          Reporter: mark at klomp dot org
                CC: devurandom at gmx dot net, elfutils-devel at sourceware dot org,
                    mark at klomp dot org, slyfox at inbox dot ru,
                    unassigned at sourceware dot org
        Depends on: 23916
  Target Milestone: ---

+++ This bug was initially created as a clone of Bug #23916 +++

The ELF compression header has a field (ch_addralign) that is set to the
alignment of the uncompressed section. This way the section itself can have a
different alignment than the decompressed section. bfd (and readelf) however
explicitly make the section sh_addralign and ch_addralign equal. It also always
sets the alignment to 1 which is wrong when using a Elf32_Chdr (which has
alignment of 4) or Elf64_Chdr (which has alignment of 8).

This shows up with tools that use elfutils libelf which sets up the alignment

First gas creates a compressed section with on alignment of 1.
Second libelf accepts this, but corrects the alignment when it
writes out the section.
Third bfd_check_compression_header sanity checks the section alignment,
but it checks that the compressed and decompressed alignment is equal?!?
I think it wanted to check that the alignment is a power of 2 instead.

Referenced Bugs:

[Bug 23916] [bisected] elifutils-0.175 broke kernel's objtool (elifutils-0.173
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