Re: [PATCH] PR ld/16322: ld fails to generate GNU_RELRO segment

[Alan Modra <amodra at gmail dot com>]

On Fri, Jan 10, 2014 at 03:19:30PM +1030, Alan Modra wrote:
> I think what we should do instead is fix Jakub's original code setting
> up the PR_GNU_RELRO segment from the PT_LOAD segment..

This is what I ended up committing.

	PR ld/14207
	PR ld/16322
	PR binutils/16323
bfd/
	* elf.c (assign_file_positions_for_load_sections): Revert last change.
	(assign_file_positions_for_non_load_sections): When setting up
	PT_GNU_RELRO header, don't require a corresponding PT_LOAD
	header that completely covers the relro region.
ld/
	* ldlang.c (lang_size_sections): Remove unneeded RELRO base
	adjust.  Tidy comments.
	* ld.texinfo (DATA_SEGMENT_RELRO_END): Correct description.
ld/testsuite/
	* ld-x86-64/pr14207.d: Adjust

diff --git a/bfd/elf.c b/bfd/elf.c
index 870e281..3815e32 100644
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -4376,7 +4376,6 @@ assign_file_positions_for_load_sections (bfd *abfd,
   unsigned int alloc;
   unsigned int i, j;
   bfd_vma header_pad = 0;
-  bfd_vma relro_start = 0, relro_end = 0;
 
   if (link_info == NULL
       && !_bfd_elf_map_sections_to_segments (abfd, link_info))
@@ -4447,23 +4446,6 @@ assign_file_positions_for_load_sections (bfd *abfd,
     header_pad -= off;
   off += header_pad;
 
-  /* Get start and end of PT_GNU_RELRO segment.  */
-  if (link_info != NULL)
-    {
-      relro_start = link_info->relro_start;
-      relro_end = link_info->relro_end;
-    }
-  else
-    {
-      for (m = elf_seg_map (abfd); m != NULL; m = m->next)
-	if (m->p_type == PT_GNU_RELRO)
-	  {
-	    relro_start = m->p_paddr;
-	    relro_end = relro_start + m->p_size;
-	    break;
-	  }
-    }
-
   for (m = elf_seg_map (abfd), p = phdrs, j = 0;
        m != NULL;
        m = m->next, p++, j++)
@@ -4807,22 +4789,6 @@ assign_file_positions_for_load_sections (bfd *abfd,
 	    }
 	}
 
-      if (relro_start != 0
-	  && p->p_type == PT_LOAD
-	  && p->p_vaddr >= relro_start)
-	{
-	  /* If PT_LOAD segment doesn't fit PT_GNU_RELRO segment,
-	     adjust its p_filesz and p_memsz.  */
-	  if (p->p_vaddr + p->p_filesz < relro_end)
-	    {
-	      bfd_vma adjust = relro_end - (p->p_vaddr + p->p_filesz);
-	      p->p_filesz += adjust;
-	      off += adjust;
-	    }
-	  if (p->p_vaddr + p->p_memsz < relro_end)
-	    p->p_memsz += relro_end - (p->p_vaddr + p->p_memsz);
-	}
-
       off -= off_adjust;
 
       /* Check that all sections are in a PT_LOAD segment.
@@ -5024,14 +4990,11 @@ assign_file_positions_for_non_load_sections (bfd *abfd,
 		{
 		  if (lp->p_type == PT_LOAD
 		      && lp->p_vaddr < link_info->relro_end
-		      && lp->p_vaddr + lp->p_filesz >= link_info->relro_end
 		      && lm->count != 0
 		      && lm->sections[0]->vma >= link_info->relro_start)
 		    break;
 		}
 
-	      /* PR ld/14207.  If the RELRO segment doesn't fit in the
-		 LOAD segment, it should be removed.  */
 	      BFD_ASSERT (lm != NULL);
 	    }
 	  else
diff --git a/ld/ld.texinfo b/ld/ld.texinfo
index 398dd59..ae3d568 100644
--- a/ld/ld.texinfo
+++ b/ld/ld.texinfo
@@ -5916,13 +5916,15 @@ evaluation purposes.
 @item DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp})
 @kindex DATA_SEGMENT_RELRO_END(@var{offset}, @var{exp})
 This defines the end of the @code{PT_GNU_RELRO} segment when
-@samp{-z relro} option is used.  Second argument is returned.
+@samp{-z relro} option is used.
 When @samp{-z relro} option is not present, @code{DATA_SEGMENT_RELRO_END}
 does nothing, otherwise @code{DATA_SEGMENT_ALIGN} is padded so that
 @var{exp} + @var{offset} is aligned to the most commonly used page
 boundary for particular target.  If present in the linker script,
 it must always come in between @code{DATA_SEGMENT_ALIGN} and
-@code{DATA_SEGMENT_END}.
+@code{DATA_SEGMENT_END}.  Evaluates to the second argument plus any
+padding needed at the end of the @code{PT_GNU_RELRO} segment due to
+section alignment.
 
 @smallexample
   . = DATA_SEGMENT_RELRO_END(24, .);
diff --git a/ld/ldlang.c b/ld/ldlang.c
index 7851615..c5e7a3d 100644
--- a/ld/ldlang.c
+++ b/ld/ldlang.c
@@ -5362,18 +5362,14 @@ lang_size_sections (bfd_boolean *relax, bfd_boolean check_regions)
       && link_info.relro && expld.dataseg.relro_end)
     {
       /* If DATA_SEGMENT_ALIGN DATA_SEGMENT_RELRO_END pair was seen, try
-	 to put expld.dataseg.relro on a (common) page boundary.  */
-      bfd_vma min_base, old_base, relro_end, maxpage;
+	 to put expld.dataseg.relro_end on a (common) page boundary.  */
+      bfd_vma min_base, relro_end, maxpage;
 
       expld.dataseg.phase = exp_dataseg_relro_adjust;
       maxpage = expld.dataseg.maxpagesize;
       /* MIN_BASE is the absolute minimum address we are allowed to start the
 	 read-write segment (byte before will be mapped read-only).  */
       min_base = (expld.dataseg.min_base + maxpage - 1) & ~(maxpage - 1);
-      /* OLD_BASE is the address for a feasible minimum address which will
-	 still not cause a data overlap inside MAXPAGE causing file offset skip
-	 by MAXPAGE.  */
-      old_base = expld.dataseg.base;
       expld.dataseg.base += (-expld.dataseg.relro_end
 			     & (expld.dataseg.pagesize - 1));
       /* Compute the expected PT_GNU_RELRO segment end.  */
@@ -5389,9 +5385,9 @@ lang_size_sections (bfd_boolean *relax, bfd_boolean check_regions)
       if (expld.dataseg.relro_end > relro_end)
 	{
 	  /* The alignment of sections between DATA_SEGMENT_ALIGN
-	     and DATA_SEGMENT_RELRO_END caused huge padding to be
-	     inserted at DATA_SEGMENT_RELRO_END.  Try to start a bit lower so
-	     that the section alignments will fit in.  */
+	     and DATA_SEGMENT_RELRO_END can cause excessive padding to
+	     be inserted at DATA_SEGMENT_RELRO_END.  Try to start a
+	     bit lower so that the section alignments will fit in.  */
 	  asection *sec;
 	  unsigned int max_alignment_power = 0;
 
@@ -5405,9 +5401,10 @@ lang_size_sections (bfd_boolean *relax, bfd_boolean check_regions)
 
 	  if (((bfd_vma) 1 << max_alignment_power) < expld.dataseg.pagesize)
 	    {
-	      if (expld.dataseg.base - (1 << max_alignment_power) < old_base)
-		expld.dataseg.base += expld.dataseg.pagesize;
-	      /* Properly align base to max_alignment_power.  */
+	      /* Aligning the adjusted base guarantees the padding
+		 between sections won't change.  This is better than
+		 simply subtracting 1 << max_alignment_power which is
+		 what we used to do here.  */
 	      expld.dataseg.base &= ~((1 << max_alignment_power) - 1);
 	      lang_reset_memory_regions ();
 	      one_lang_size_sections_pass (relax, check_regions);
diff --git a/ld/testsuite/ld-x86-64/pr14207.d b/ld/testsuite/ld-x86-64/pr14207.d
index b1e2d5a..d4e22a1 100644
--- a/ld/testsuite/ld-x86-64/pr14207.d
+++ b/ld/testsuite/ld-x86-64/pr14207.d
@@ -11,7 +11,7 @@ There are 4 program headers, starting at offset 64
 Program Headers:
   Type           Offset   VirtAddr           PhysAddr           FileSiz  MemSiz   Flg Align
   LOAD           0x000000 0x0000000000000000 0x0000000000000000 0x0001e0 0x0001e0 R   0x200000
-  LOAD           0x000b48 0x0000000000200b48 0x0000000000200b48 0x0004b8 0x000cf8 RW  0x200000
+  LOAD           0x000b48 0x0000000000200b48 0x0000000000200b48 0x0004b0 0x000cf8 RW  0x200000
   DYNAMIC        0x000b90 0x0000000000200b90 0x0000000000200b90 0x0001c0 0x0001c0 RW  0x8
   GNU_RELRO      0x000b48 0x0000000000200b48 0x0000000000200b48 0x0004b8 0x0004b8 R   0x1
 


-- 
Alan Modra
Australia Development Lab, IBM