[binutils-gdb] MIPS/LD: Fix crashing with a discarded dynamic relocation section

[Maciej W.Rozycki <macro at sourceware dot org>]

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=db841b6fcd8b3bc2e6d6774e81c14dfbb9ac815d

commit db841b6fcd8b3bc2e6d6774e81c14dfbb9ac815d
Author: Maciej W. Rozycki <macro@mips.com>
Date:   Fri Jul 20 13:21:33 2018 +0100

    MIPS/LD: Fix crashing with a discarded dynamic relocation section
    
    Fix a crash that occurs in `_bfd_mips_elf_finish_dynamic_sections' if a
    dynamic relocation section has been created, but marked to be discarded
    by an assignment to the /DISCARD/ output section in a linker script.
    In that case the output section is the absolute section, which has no
    ELF section data attached, so trying to set its `sh_size' parameter
    causes a null pointer dereference.
    
    This is only done as the value for the DT_RELSZ dynamic entry is being
    set, so fix the problem by not creating DT_REL, DT_RELSZ or DT_RELENT
    dynamic entries in the first place if the dynamic relocation section
    will not be output, as with no dynamic relocation data present these
    would not serve their purpose anyway.
    
    Add a generic ELF test case to verify that no dynamic relocation data is
    reported in the dynamic segment.
    
    	bfd/
    	* elfxx-mips.c (_bfd_mips_elf_size_dynamic_sections): Do not
    	create DT_REL, DT_RELSZ or DT_RELENT dynamic entries if the
    	dynamic relocation section will be discarded from output.
    	(_bfd_mips_elf_finish_dynamic_sections) <DT_RELSZ>: Assert that
    	the dynamic relocation section will be retained in output.
    
    	ld/
    	* testsuite/ld-elf/reloc-discard.d: New test.
    	* testsuite/ld-elf/reloc-discard.ld: New test linker script.
    	* testsuite/ld-elf/reloc-discard.s: New test source.

Diff:
---
 bfd/ChangeLog                        |  8 ++++++++
 bfd/elfxx-mips.c                     |  4 +++-
 ld/ChangeLog                         |  6 ++++++
 ld/testsuite/ld-elf/reloc-discard.d  | 10 ++++++++++
 ld/testsuite/ld-elf/reloc-discard.ld |  6 ++++++
 ld/testsuite/ld-elf/reloc-discard.s  |  2 ++
 6 files changed, 35 insertions(+), 1 deletion(-)

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index c5960e6..9b7048c 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,11 @@
+2018-07-20  Maciej W. Rozycki  <macro@mips.com>
+
+	* elfxx-mips.c (_bfd_mips_elf_size_dynamic_sections): Do not
+	create DT_REL, DT_RELSZ or DT_RELENT dynamic entries if the
+	dynamic relocation section will be discarded from output.
+	(_bfd_mips_elf_finish_dynamic_sections) <DT_RELSZ>: Assert that
+	the dynamic relocation section will be retained in output.
+
 2018-07-18  Maciej W. Rozycki  <macro@mips.com>
 
 	* xcofflink.c (xcoff_write_global_symbol): Fix symbol type
diff --git a/bfd/elfxx-mips.c b/bfd/elfxx-mips.c
index d919423..cc767ea 100644
--- a/bfd/elfxx-mips.c
+++ b/bfd/elfxx-mips.c
@@ -9890,7 +9890,8 @@ _bfd_mips_elf_size_dynamic_sections (bfd *output_bfd,
 	}
       else
 	{
-	  if (sreldyn && sreldyn->size > 0)
+	  if (sreldyn && sreldyn->size > 0
+	      && !bfd_is_abs_section (sreldyn->output_section))
 	    {
 	      if (! MIPS_ELF_ADD_DYNAMIC_ENTRY (info, DT_REL, 0))
 		return FALSE;
@@ -11798,6 +11799,7 @@ _bfd_mips_elf_finish_dynamic_sections (bfd *output_bfd,
 				   : sizeof (Elf32_External_Rel)));
 	      /* Adjust the section size too.  Tools like the prelinker
 		 can reasonably expect the values to the same.  */
+	      BFD_ASSERT (!bfd_is_abs_section (s->output_section));
 	      elf_section_data (s->output_section)->this_hdr.sh_size
 		= dyn.d_un.d_val;
 	      break;
diff --git a/ld/ChangeLog b/ld/ChangeLog
index c2f6b28..8c7d2df 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,9 @@
+2018-07-20  Maciej W. Rozycki  <macro@mips.com>
+
+	* testsuite/ld-elf/reloc-discard.d: New test.
+	* testsuite/ld-elf/reloc-discard.ld: New test linker script.
+	* testsuite/ld-elf/reloc-discard.s: New test source.
+
 2018-07-18  Nick Clifton  <nickc@redhat.com>
 
 	* po/fr.po: Updated French translation.
diff --git a/ld/testsuite/ld-elf/reloc-discard.d b/ld/testsuite/ld-elf/reloc-discard.d
new file mode 100644
index 0000000..b8aad88
--- /dev/null
+++ b/ld/testsuite/ld-elf/reloc-discard.d
@@ -0,0 +1,10 @@
+#name: Discarded dynamic relocation section
+#ld: -shared -T reloc-discard.ld
+#readelf: -r --use-dynamic
+#target: [check_shared_lib_support]
+#source: reloc-discard.s
+#xfail: nds32*-*-* tic6x-*-*
+# Need to figure out how to pass `-fpic' for NDS32 or `-mpic -mpid=near'
+# for TI C6X targets to GAS for this test.
+
+There are no dynamic relocations in this file\.
diff --git a/ld/testsuite/ld-elf/reloc-discard.ld b/ld/testsuite/ld-elf/reloc-discard.ld
new file mode 100644
index 0000000..b16b80a
--- /dev/null
+++ b/ld/testsuite/ld-elf/reloc-discard.ld
@@ -0,0 +1,6 @@
+SECTIONS
+{
+  /* .dynamic needs to go first with MIPS IRIX-style emulations.  */
+  .dynamic : { *(.dynamic) }
+  /DISCARD/ : { *(.rel.dyn) *(.rela.dyn) }
+}
diff --git a/ld/testsuite/ld-elf/reloc-discard.s b/ld/testsuite/ld-elf/reloc-discard.s
new file mode 100644
index 0000000..23f187a
--- /dev/null
+++ b/ld/testsuite/ld-elf/reloc-discard.s
@@ -0,0 +1,2 @@
+	.data
+	.dc.a	foo