Squash readelf warning on zero sh_link reloc section

On readelf examining a static executable built with current glibc,
we get a silly warning.

Section Headers:
  [Nr] Name              Type            Address          Off    Size   ES Flg Lk Inf Al
  [ 0]                   NULL            0000000000000000 000000 000000 00      0   0  0
  [ 1] .note.ABI-tag     NOTE            0000000000400190 000190 000020 00   A  0   0  4
  [ 2] .note.gnu.build-id NOTE            00000000004001b0 0001b0 000024 00   A  0   0  4
readelf: Warning: [ 3]: Link field (0) should index a symtab section.
  [ 3] .rela.plt         RELA            00000000004001d8 0001d8 000228 18  AI  0  20  8

This .rela.plt section contains only IRELATIVE relocations (which have
symbol index zero), so it isn't appropriate to warn.  A zero sh_link
section is deliberately chosen for such a section (see PR10337 and
PR23850).

So this patch disables the SHT_REL* sh_link warning.  I've also
removed the .rel.dyn/.rela.dyn section name test to disable the
sh_info warning for SHT_REL* sections.  While relocation sections in
an executable need not specify the section they relocate (the
relocation sh_offset field is an address, not a section offset), that
isn't true in a relocatable file where sh_offset is relative to a
section.  If .rela.dyn happens to exist in an ET_REL object it must
specify a valid section.

	* readelf.c (process_section_headers): Don't warn on a zero
	sh_info or sh_link for any reloc section in an executable or
	shared library.  Do warn for .rel.dyn/.rela.dyn in ET_REL.

2 files changed, 26 insertions, 20 deletions

diff --git a/binutils/ChangeLog b/binutils/ChangeLog
index 8404b67..662ee24 100644
--- a/binutils/ChangeLog
+++ b/binutils/ChangeLog
@@ -1,3 +1,9 @@
+2018-11-02  Alan Modra  <amodra@gmail.com>
+
+	* readelf.c (process_section_headers): Don't warn on a zero
+	sh_info or sh_link for any reloc section in an executable or
+	shared library.  Do warn for .rel.dyn/.rela.dyn in ET_REL.
+
 2018-11-01  Thomas Preud'homme  <thomas.preudhomme@linaro.org>
 
 	* testsuite/config/default.exp: Define LD, LDFLAGS and
diff --git a/binutils/readelf.c b/binutils/readelf.c
index d8d0d6e..3974400 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -6299,14 +6299,21 @@ process_section_headers (Filedata * filedata)
       /* Check the sh_link field.  */
       switch (section->sh_type)
 	{
+	case SHT_REL:
+	case SHT_RELA:
+	  if (section->sh_link == 0
+	      && (filedata->file_header.e_type == ET_EXEC
+		  || filedata->file_header.e_type == ET_DYN))
+	    /* A dynamic relocation section where all entries use a
+	       zero symbol index need not specify a symtab section.  */
+	    break;
+	  /* Fall through.  */
 	case SHT_SYMTAB_SHNDX:
 	case SHT_GROUP:
 	case SHT_HASH:
 	case SHT_GNU_HASH:
 	case SHT_GNU_versym:
-	case SHT_REL:
-	case SHT_RELA:
-	  if (section->sh_link < 1
+	  if (section->sh_link == 0
 	      || section->sh_link >= filedata->file_header.e_shnum
 	      || (filedata->section_headers[section->sh_link].sh_type != SHT_SYMTAB
 		  && filedata->section_headers[section->sh_link].sh_type != SHT_DYNSYM))
@@ -6320,7 +6327,7 @@ process_section_headers (Filedata * filedata)
 	case SHT_GNU_verneed:
 	case SHT_GNU_verdef:
 	case SHT_GNU_LIBLIST:
-	  if (section->sh_link < 1
+	  if (section->sh_link == 0
 	      || section->sh_link >= filedata->file_header.e_shnum
 	      || filedata->section_headers[section->sh_link].sh_type != SHT_STRTAB)
 	    warn (_("[%2u]: Link field (%u) should index a string section.\n"),
@@ -6353,7 +6360,13 @@ process_section_headers (Filedata * filedata)
 	{
 	case SHT_REL:
 	case SHT_RELA:
-	  if (section->sh_info < 1
+	  if (section->sh_info == 0
+	      && (filedata->file_header.e_type == ET_EXEC
+		  || filedata->file_header.e_type == ET_DYN))
+	    /* Dynamic relocations apply to segments, so they do not
+	       need to specify the section they relocate.  */
+	    break;
+	  if (section->sh_info == 0
 	      || section->sh_info >= filedata->file_header.e_shnum
 	      || (filedata->section_headers[section->sh_info].sh_type != SHT_PROGBITS
 		  && filedata->section_headers[section->sh_info].sh_type != SHT_NOBITS
@@ -6363,21 +6376,8 @@ process_section_headers (Filedata * filedata)
 		  && filedata->section_headers[section->sh_info].sh_type != SHT_PREINIT_ARRAY
 		  /* FIXME: Are other section types valid ?  */
 		  && filedata->section_headers[section->sh_info].sh_type < SHT_LOOS))
-	    {
-	      if (section->sh_info == 0
-		  && (filedata->file_header.e_type == ET_EXEC
-		      || filedata->file_header.e_type == ET_DYN
-		      /* These next two tests may be redundant, but
-			 they have been left in for paranoia's sake.  */
-		      || streq (SECTION_NAME (section), ".rel.dyn")
-		      || streq (SECTION_NAME (section), ".rela.dyn")))
-		/* Dynamic relocations apply to segments, not sections, so
-		   they do not need an sh_info value.  */
-		;
-	      else
-		warn (_("[%2u]: Info field (%u) should index a relocatable section.\n"),
-		      i, section->sh_info);
-	    }
+	    warn (_("[%2u]: Info field (%u) should index a relocatable section.\n"),
+		  i, section->sh_info);
 	  break;
 
 	case SHT_DYNAMIC: