Re: [gold] arm: fix exidx in relocatable builds

[Yury Usishchev <y dot usishchev at samsung dot com>]

Forgot to attach the file=)

commit 84d5b00ce910369002227cd7e380660b39da8ba9
Author: Yury Usishchev <y.usishchev@samsung.com>
Date:   Mon Jan 25 17:47:01 2016 +0300

    add relaxation to relocatable builds, only fix exidx there

diff --git a/gold/arm.cc b/gold/arm.cc
index 9716195..4984ff8 100644
--- a/gold/arm.cc
+++ b/gold/arm.cc
@@ -2520,7 +2520,8 @@ class Target_arm : public Sized_target<32, big_endian>
   // not doing relocatable linking.
   bool
   do_may_relax() const
-  { return !parameters->options().relocatable(); }
+  { return 1; }
+  //{ return !parameters->options().relocatable(); }
 
   bool
   do_relax(int, const Input_objects*, Symbol_table*, Layout*, const Task*);
@@ -5634,6 +5635,7 @@ Arm_exidx_fixup::process_exidx_section(
   bool prev_delete_entry = false;
   gold_assert(this->section_offset_map_ == NULL);
 
+  if(!parameters->options().relocatable())
   for (section_size_type i = 0; i < section_size; i += 8)
     {
       typedef typename elfcpp::Swap<32, big_endian>::Valtype Valtype;
@@ -5665,6 +5667,7 @@ Arm_exidx_fixup::process_exidx_section(
 
   // If section offset map is not NULL, make an entry for the end of
   // section.
+  if(!parameters->options().relocatable())
   if (this->section_offset_map_ != NULL)
     update_offset_map(section_size - 1, deleted_bytes, prev_delete_entry);
 
@@ -6083,9 +6086,11 @@ Arm_output_section<big_endian>::fix_exidx_coverage(
     }
 
   // Insert an EXIDX_CANTUNWIND entry at the end of output if necessary.
-  exidx_fixup.add_exidx_cantunwind_as_needed();
+  if(parameters->options().relocatable())
+    exidx_fixup.add_exidx_cantunwind_as_needed();
 
   // Remove any known EXIDX input sections that are not processed.
+  if(!parameters->options().relocatable())
   for (Input_section_list::const_iterator p = input_sections.begin();
        p != input_sections.end();
        ++p)
@@ -12203,11 +12208,42 @@ Target_arm<big_endian>::do_relax(
     const Task* task)
 {
   // No need to generate stubs if this is a relocatable link.
-  gold_assert(!parameters->options().relocatable());
+  bool done_exidx_fixup = false;
+  if (pass == 1)
+    {
+      Arm_output_section<big_endian>* exidx_output_section = NULL;
+      for (Layout::Section_list::const_iterator p =
+	     layout->section_list().begin();
+	   p != layout->section_list().end();
+	   ++p)
+	if ((*p)->type() == elfcpp::SHT_ARM_EXIDX)
+	  {
+	    if (exidx_output_section == NULL)
+	      exidx_output_section =
+		Arm_output_section<big_endian>::as_arm_output_section(*p);
+	    else
+	      // We cannot handle this now.
+	      gold_error(_("multiple SHT_ARM_EXIDX sections %s and %s in a "
+			   "non-relocatable link"),
+			  exidx_output_section->name(),
+			  (*p)->name());
+	  }
+
+      if (exidx_output_section != NULL)
+	{
+	  this->fix_exidx_coverage(layout, input_objects, exidx_output_section,
+				   symtab, task);
+	  done_exidx_fixup = true;
+	}
+    }
+
+  // if not relocatable - we dont need second run
+  if(parameters->options().relocatable())
+    return done_exidx_fixup;
+  //gold_assert(!parameters->options().relocatable());
 
   // If this is the first pass, we need to group input sections into
   // stub groups.
-  bool done_exidx_fixup = false;
   typedef typename Stub_table_list::iterator Stub_table_iterator;
   if (pass == 1)
     {
@@ -12252,30 +12288,6 @@ Target_arm<big_endian>::do_relax(
       group_sections(layout, stub_group_size, stubs_always_after_branch, task);
 
       // Also fix .ARM.exidx section coverage.
-      Arm_output_section<big_endian>* exidx_output_section = NULL;
-      for (Layout::Section_list::const_iterator p =
-	     layout->section_list().begin();
-	   p != layout->section_list().end();
-	   ++p)
-	if ((*p)->type() == elfcpp::SHT_ARM_EXIDX)
-	  {
-	    if (exidx_output_section == NULL)
-	      exidx_output_section =
-		Arm_output_section<big_endian>::as_arm_output_section(*p);
-	    else
-	      // We cannot handle this now.
-	      gold_error(_("multiple SHT_ARM_EXIDX sections %s and %s in a "
-			   "non-relocatable link"),
-			  exidx_output_section->name(),
-			  (*p)->name());
-	  }
-
-      if (exidx_output_section != NULL)
-	{
-	  this->fix_exidx_coverage(layout, input_objects, exidx_output_section,
-				   symtab, task);
-	  done_exidx_fixup = true;
-	}
     }
   else
     {

BR,
Yury Usishchev

Yury Usishchev <y.usishchev@samsung.com> writes:
> Hello all!
>
> I want to fix PR19524 (https://sourceware.org/bugzilla/show_bug.cgi?id=19524).
> In relocatable builds linker does not fix unwind info, leaving some gaps, this can cause problems in unwinder including
> segmentation faults.
> The same issue was fixed for BFD linker in PR17323 (https://sourceware.org/bugzilla/show_bug.cgi?id=17323).
>
> To fix the problem I suppose I need to add part of relaxation where exidx fixup is done to relocatable builds and
> generate correct relocation for new unwind info.
>
> For now I managed to generate required 'cantunwind' but not the relocation, and it is done in very hacky way (see
> attached).
>
> Could some Gold hacker help me with advice on creating the fix? Here are the main issues I would like to discuss:
> 1) Where exidx fix should be called from in relocatable builds?(how wrong is it to run relaxation in such builds)
> 2) Is it possible to create a relocation in Gold? If so, how can I achieve this?
> 3) Where should this relocation be created and placed?
>
> Any help will be appreciated.
>
> BR,
> Yury Usishchev