[PATCH v2 1/2] aarch64: Fix DT_RELR support with discarded sections

[Szabolcs Nagy]

In case of discarded sections, via /DISCARD/ or .gnu.linkonce,
relr relocation accounting was wrong.  This broke building linux.

The issue was that the *_relocate_section logic was copied to
*_late_size_sections to record relative relocations that can
be packed, however *_relocate_section is not called on sections
that are discarded, while record_relr_non_got_relocs is called
for all input sections. The fix is to filter out the discarded
sections with the same logic that is used to count non-GOT
relocs for local symbols earlier.

GOT relocations are affected too if all sections are discarded
that reference the GOT entry of a particular symbol, however
this can cause unused GOT entries independently of DT_RELR, and
the only difference with DT_RELR is that a relative reloc may be
emitted instead of a R_AARCH64_NONE for the unused GOT entry
which is acceptable. A proper fix would require redoing the GOT
refcounting after we know the discarded sections.
---
v2:
- only commit msg update: i realized that the GOT case is not
  handled right when DT_RELR is disabled so there is no point
  trying to fix that here and unnecessary relative relocation
  in such corner-case is acceptable. i updated the test case
  patch to cover the GOT cases that currently work.
---
 bfd/elfnn-aarch64.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/bfd/elfnn-aarch64.c b/bfd/elfnn-aarch64.c
index 81f1a646125..02873f2ceb2 100644
--- a/bfd/elfnn-aarch64.c
+++ b/bfd/elfnn-aarch64.c
@@ -9327,6 +9327,10 @@ record_relr_non_got_relocs (bfd *input_bfd, struct bfd_link_info *info,
     return true;
   if (sec->alignment_power == 0)
     return true;
+  if (!bfd_is_abs_section (sec)
+      && bfd_is_abs_section (sec->output_section))
+    /* Input section has been discarded.  */
+    return true;
   sreloc = elf_section_data (sec)->sreloc;
   if (sreloc == NULL)
     return true;
-- 
2.25.1