[PATCH 1/5] gold: Properly align the NT_GNU_PROPERTY_TYPE_0 note

[H.J. Lu]

On Sat, Oct 10, 2020 at 5:20 PM Fangrui Song <i@maskray.me> wrote:
>
>
> On 2020-10-10, H.J. Lu via Binutils wrote:
> >The NT_GNU_PROPERTY_TYPE_0 note should be aligned to 8 bytes for 64-bit
> >ELF as specified by gABI.  A note section can be only placed in a PT_NOTE
> >segment with the same alignment.
> >
> >       PR gold/22914
> >       PR gold/23535
> >       * layout.cc (Layout::attach_allocated_section_to_segment): Place
> >       a note section in a PT_NOTE segment with the same alignment.  Set
> >       the alignment of the PT_NOTE segment from the alignment of the
> >       note section.
> >       (Layout::create_note): Align the NT_GNU_PROPERTY_TYPE_0 note to 8
> >       bytes for 64-bit ELF.
> >       (Layout::segment_precedes): Place segments with larger alignments
> >       first.
> >       * output.cc (Output_segment::Output_segment): Initialize align_.
> >       * output.h (Output_segment): Add align, set_align and align_.
> >       * testsuite/Makefile.am (gnu_property_test.stdout): Pass -lhSWn
> >       to $(TEST_READELF).
> >       (gnu_property_test): Pass --build-id to ld.
> >       * testsuite/Makefile.in: Regenerated.
> >       * testsuite/gnu_property_test.sh (check_alignment): New.
> >       Use check_alignment to check the NT_GNU_PROPERTY_TYPE_0 note
> >       alignment.  Verify that there are 2 PT_NOTE segments.
> >---
> > gold/layout.cc                      | 15 ++++++++++++++-
> > gold/output.cc                      |  1 +
> > gold/output.h                       | 12 ++++++++++++
> > gold/testsuite/Makefile.am          |  4 ++--
> > gold/testsuite/Makefile.in          |  4 ++--
> > gold/testsuite/gnu_property_test.sh | 20 ++++++++++++++++++++
> > 6 files changed, 51 insertions(+), 5 deletions(-)
> >
> >diff --git a/gold/layout.cc b/gold/layout.cc
> >index 13e533aaf21..6948ff7214c 100644
> >--- a/gold/layout.cc
> >+++ b/gold/layout.cc
> >@@ -2062,12 +2062,15 @@ Layout::attach_allocated_section_to_segment(const Target* target,
> >   // segment.
> >   if (os->type() == elfcpp::SHT_NOTE)
> >     {
> >+      uint64_t os_align = os->addralign();
> >+
> >       // See if we already have an equivalent PT_NOTE segment.
> >       for (p = this->segment_list_.begin();
> >          p != segment_list_.end();
> >          ++p)
> >       {
> >         if ((*p)->type() == elfcpp::PT_NOTE
> >+            && (*p)->align() == os_align
> >             && (((*p)->flags() & elfcpp::PF_W)
> >                 == (seg_flags & elfcpp::PF_W)))
> >           {
> >@@ -2081,6 +2084,7 @@ Layout::attach_allocated_section_to_segment(const Target* target,
> >         Output_segment* oseg = this->make_output_segment(elfcpp::PT_NOTE,
> >                                                          seg_flags);
> >         oseg->add_output_section_to_nonload(os, seg_flags);
> >+        oseg->set_align(os_align);
> >       }
> >     }
>
> LG. I used the same approach for LLD: there will be two PT_NOTE if there are
> SHT_NOTE of mixed alignments.
>
> >@@ -3184,6 +3188,10 @@ Layout::create_note(const char* name, int note_type,
> > #else
> >   const int size = 32;
> > #endif
> >+  // The NT_GNU_PROPERTY_TYPE_0 note conforms to gABI.
> >+  const int addralign = ((note_type == elfcpp::NT_GNU_PROPERTY_TYPE_0
> >+                       ? parameters->target().get_size()
> >+                       : size) / 8);
>
> This comment may be incorrect. gABI uses 64-bit integers on ELFCLASS64.
> A NT_GNU_PROPERTY_TYPE_0 has an alignment of 8 but its elements still do
> not conform to gABI. This can be Linux ABI or GNU ABI.
>

Changed to

// The NT_GNU_PROPERTY_TYPE_0 note is aligned to the pointer size.

-- 
H.J.