[GOLD] question about gold handling SPARC style .rela.plt, .rela.plt overlapping

[GOLD] question about gold handling SPARC style .rela.plt, .rela.plt overlapping

[WANG.Jiong]

Hi David & Ian,

   currently, I am porting gold linker for a private target which allow 
PLTREL overlapping

   so, I met exactly the same problem as you have discussed two years ago

   http://sourceware.org/ml/binutils/2010-02/msg00140.html

   I see you have done a fix with the following logic:

   1. .rela.dyn,  .rela.plt are seperate
   2. generate DT_RELA only when there is .rela.dyn, and DT_RELASZ be 
the total size of both .rela.dyn and .rela.plt

   But, If there is no .rela.dyn, without DT_RELA, it seems dynamic 
linker behave incorrectly when ELF_MACHINE_PLTREL_OVERLAP defined

   I checked the implementation of  _ELF_DYNAMIC_DO_RELOC in glib

   elf/dynamic-link.h:260
   # define _ELF_DYNAMIC_DO_RELOC(RELOC, reloc, map, do_lazy, 
skip_ifunc, test_rel)

   without DT_REL or DT_RELA,  ranges[0] are not initialized properly.

   So, should we always generate DT_RELA, DT_RELASZ, DT_RELAENT, and 
make DT_RELA, DT_RELASZ exactly the same value as DT_JMPREL, DT_PLTRELSZ ?

   that is, for the following condition check in 
Layout::add_target_dynamic_tags

4344   if (dyn_rel != NULL && dyn_rel->output_section() != NULL)
4345 {
4346       odyn->add_section_address(use_rel ? elfcpp::DT_REL : 
elfcpp::DT_RELA,
4347 dyn_rel->output_section());
4348       if (plt_rel != NULL
4349           && plt_rel->output_section() != NULL
4350           && dynrel_includes_plt)

    should we check dynrel_includes_plt even when dyn_rel == NULL ?

   or I have misunderstood something ?

   thanks very much

---
Regards,
WANG.Jiong

Re: [GOLD] question about gold handling SPARC style .rela.plt, .rela.plt overlapping

[Ian Lance Taylor]

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On Tue, Aug 7, 2012 at 1:24 AM, WANG.Jiong <wong.kwongyuan@gmail.com> wrote:
>
>   currently, I am porting gold linker for a private target which allow
> PLTREL overlapping
>
> ...
>
>   So, should we always generate DT_RELA, DT_RELASZ, DT_RELAENT, and make
> DT_RELA, DT_RELASZ exactly the same value as DT_JMPREL, DT_PLTRELSZ ?
>
>   that is, for the following condition check in
> Layout::add_target_dynamic_tags
>
> 4344   if (dyn_rel != NULL && dyn_rel->output_section() != NULL)
> 4345 {
> 4346       odyn->add_section_address(use_rel ? elfcpp::DT_REL :
> elfcpp::DT_RELA,
> 4347 dyn_rel->output_section());
> 4348       if (plt_rel != NULL
> 4349           && plt_rel->output_section() != NULL
> 4350           && dynrel_includes_plt)
>
>    should we check dynrel_includes_plt even when dyn_rel == NULL ?

Yes, I agree.  If dynrel_includes_plt && dyn_rel == NULL && plt_rel !=
NULL, we should generate the DT_REL tags.

I committed the attached patch.

Ian

2012-08-07  Ian Lance Taylor  <iant@google.com>

	* layout.cc (Layout::add_target_dynamic_tags): If
	dynrel_includes_plt but no dyn_rel, emit dynamic reloc tags for
	plt_rel.

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Index: layout.cc
===================================================================
RCS file: /cvs/src/src/gold/layout.cc,v
retrieving revision 1.231
retrieving revision 1.232
diff -u -p -r1.231 -r1.232
--- layout.cc	22 Jun 2012 18:02:24 -0000	1.231
+++ layout.cc	7 Aug 2012 13:24:47 -0000	1.232
@@ -4341,19 +4341,26 @@ Layout::add_target_dynamic_tags(bool use
 			 use_rel ? elfcpp::DT_REL : elfcpp::DT_RELA);
     }
 
-  if (dyn_rel != NULL && dyn_rel->output_section() != NULL)
+  if ((dyn_rel != NULL && dyn_rel->output_section() != NULL)
+      || (dynrel_includes_plt
+	  && plt_rel != NULL
+	  && plt_rel->output_section() != NULL))
     {
+      bool have_dyn_rel = dyn_rel != NULL && dyn_rel->output_section() != NULL;
+      bool have_plt_rel = plt_rel != NULL && plt_rel->output_section() != NULL;
       odyn->add_section_address(use_rel ? elfcpp::DT_REL : elfcpp::DT_RELA,
-				dyn_rel->output_section());
-      if (plt_rel != NULL
-	  && plt_rel->output_section() != NULL
-	  && dynrel_includes_plt)
-	odyn->add_section_size(use_rel ? elfcpp::DT_RELSZ : elfcpp::DT_RELASZ,
+				(have_dyn_rel
+				 ? dyn_rel->output_section()
+				 : plt_rel->output_section()));
+      elfcpp::DT size_tag = use_rel ? elfcpp::DT_RELSZ : elfcpp::DT_RELASZ;
+      if (have_dyn_rel && have_plt_rel && dynrel_includes_plt)
+	odyn->add_section_size(size_tag,
 			       dyn_rel->output_section(),
 			       plt_rel->output_section());
+      else if (have_dyn_rel)
+	odyn->add_section_size(size_tag, dyn_rel->output_section());
       else
-	odyn->add_section_size(use_rel ? elfcpp::DT_RELSZ : elfcpp::DT_RELASZ,
-			       dyn_rel->output_section());
+	odyn->add_section_size(size_tag, plt_rel->output_section());
       const int size = parameters->target().get_size();
       elfcpp::DT rel_tag;
       int rel_size;
@@ -4379,7 +4386,7 @@ Layout::add_target_dynamic_tags(bool use
 	}
       odyn->add_constant(rel_tag, rel_size);
 
-      if (parameters->options().combreloc())
+      if (parameters->options().combreloc() && have_dyn_rel)
 	{
 	  size_t c = dyn_rel->relative_reloc_count();
 	  if (c > 0)

Re: [GOLD] question about gold handling SPARC style .rela.plt, .rela.plt overlapping

[Jiong WANG]

Thanks!

---
Regards,
WANG.Jiong

2012/8/7 Ian Lance Taylor <iant@google.com>:
> On Tue, Aug 7, 2012 at 1:24 AM, WANG.Jiong <wong.kwongyuan@gmail.com> wrote:
>>
>>   currently, I am porting gold linker for a private target which allow
>> PLTREL overlapping
>>
>> ...
>>
>>   So, should we always generate DT_RELA, DT_RELASZ, DT_RELAENT, and make
>> DT_RELA, DT_RELASZ exactly the same value as DT_JMPREL, DT_PLTRELSZ ?
>>
>>   that is, for the following condition check in
>> Layout::add_target_dynamic_tags
>>
>> 4344   if (dyn_rel != NULL && dyn_rel->output_section() != NULL)
>> 4345 {
>> 4346       odyn->add_section_address(use_rel ? elfcpp::DT_REL :
>> elfcpp::DT_RELA,
>> 4347 dyn_rel->output_section());
>> 4348       if (plt_rel != NULL
>> 4349           && plt_rel->output_section() != NULL
>> 4350           && dynrel_includes_plt)
>>
>>    should we check dynrel_includes_plt even when dyn_rel == NULL ?
>
> Yes, I agree.  If dynrel_includes_plt && dyn_rel == NULL && plt_rel !=
> NULL, we should generate the DT_REL tags.
>
> I committed the attached patch.
>
> Ian
>
> 2012-08-07  Ian Lance Taylor  <iant@google.com>
>
>         * layout.cc (Layout::add_target_dynamic_tags): If
>         dynrel_includes_plt but no dyn_rel, emit dynamic reloc tags for
>         plt_rel.