elf: Add -z unique-symbol to avoid duplicated local symbol names

The symbol string table in the .symtab section is optional and cosmetic.
The contents of the .symtab section have no impact on run-time execution.
The symbol names in the symbol string table help distinguish addresses at
different locations.  Add a linker option, -z unique-symbol, to avoid
duplicated local symbol names in the symbol string table.

This feature was well received by the livepatch maintainers.  It not only
solves the duplicated local symbol name problem, but also would allow
livepatch to more precisely locate duplicate symbols in general for
patching.

bfd/

	PR ld/26391
	* elflink.c (elf_final_link_info): Add local_hash_table.
	(local_hash_entry): New.
	(local_hash_newfunc): Likewise.
	(elf_link_output_symstrtab): Append ".COUNT" to duplicated local
	symbols.
	(bfd_elf_final_link): Initialize and free local_hash_table for
	"-z unique-symbol".

include/

	PR ld/26391
	* bfdlink.h (bfd_link_info): Add unique_symbol.

ld/

	PR ld/26391
	* NEWS: Mention "-z unique-symbol".
	* emultempl/elf.em (gld${EMULATION_NAME}_handle_option): Handle
	"-z unique-symbol" and "-z nounique-symbol".
	* ld.texi: Document "-z unique-symbol" and "-z nounique-symbol".
	* lexsup.c (elf_static_list_options): Add "-z unique-symbol" and
	"-z nounique-symbol".
	* testsuite/ld-elf/elf.exp: Add PR ld/26391 tests.
	* testsuite/ld-elf/pr26391.nd: New file.
	* testsuite/ld-elf/pr26391.out: Likewise.
	* testsuite/ld-elf/pr26391a.c: Likewise.
	* testsuite/ld-elf/pr26391b.c: Likewise.
	* testsuite/ld-elf/pr26391c.c: Likewise.
	* testsuite/ld-elf/pr26391d.c: Likewise.

2 files changed, 177 insertions, 41 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 19415d6..4f0faa5 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,14 @@
+2020-09-12  H.J. Lu  <hongjiu.lu@intel.com>
+
+	PR ld/26391
+	* elflink.c (elf_final_link_info): Add local_hash_table.
+	(local_hash_entry): New.
+	(local_hash_newfunc): Likewise.
+	(elf_link_output_symstrtab): Append ".COUNT" to duplicated local
+	symbols.
+	(bfd_elf_final_link): Initialize and free local_hash_table for
+	"-z unique-symbol".
+
 2020-09-10  Siddhesh Poyarekar  <siddesh.poyarekar@arm.com>
 
 	* elfnn-aarch64.c (elfNN_aarch64_final_link_relocate): Revert
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 0e339f3..b693729 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -8401,8 +8401,49 @@ struct elf_final_link_info
   Elf_External_Sym_Shndx *symshndxbuf;
   /* Number of STT_FILE syms seen.  */
   size_t filesym_count;
+  /* Local symbol hash table.  */
+  struct bfd_hash_table local_hash_table;
 };
 
+struct local_hash_entry
+{
+  /* Base hash table entry structure.  */
+  struct bfd_hash_entry root;
+  /* Size of the local symbol name.  */
+  size_t size;
+  /* Number of the duplicated local symbol names.  */
+  long count;
+};
+
+/* Create an entry in the local symbol hash table.  */
+
+static struct bfd_hash_entry *
+local_hash_newfunc (struct bfd_hash_entry *entry,
+		    struct bfd_hash_table *table,
+		    const char *string)
+{
+
+  /* Allocate the structure if it has not already been allocated by a
+     subclass.  */
+  if (entry == NULL)
+    {
+      entry = bfd_hash_allocate (table,
+				 sizeof (struct local_hash_entry));
+      if (entry == NULL)
+        return entry;
+    }
+
+  /* Call the allocation method of the superclass.  */
+  entry = bfd_hash_newfunc (entry, table, string);
+  if (entry != NULL)
+    {
+      ((struct local_hash_entry *) entry)->count = 0;
+      ((struct local_hash_entry *) entry)->size = 0;
+    }
+
+  return entry;
+}
+
 /* This struct is used to pass information to elf_link_output_extsym.  */
 
 struct elf_outext_info
@@ -9666,23 +9707,66 @@ elf_link_output_symstrtab (struct elf_final_link_info *flinfo,
       /* Call _bfd_elf_strtab_offset after _bfd_elf_strtab_finalize
 	 to get the final offset for st_name.  */
       char *versioned_name = (char *) name;
-      if (h != NULL && h->versioned == versioned && h->def_dynamic)
-	{
-	  /* Keep only one '@' for versioned symbols defined in shared
-	     objects.  */
-	  char *version = strrchr (name, ELF_VER_CHR);
-	  char *base_end = strchr (name, ELF_VER_CHR);
-	  if (version != base_end)
-	    {
-	      size_t base_len;
-	      size_t len = strlen (name);
-	      versioned_name = bfd_alloc (flinfo->output_bfd, len);
-	      if (versioned_name == NULL)
+      if (h != NULL)
+	{
+	  if (h->versioned == versioned && h->def_dynamic)
+	    {
+	      /* Keep only one '@' for versioned symbols defined in
+	         shared objects.  */
+	      char *version = strrchr (name, ELF_VER_CHR);
+	      char *base_end = strchr (name, ELF_VER_CHR);
+	      if (version != base_end)
+		{
+		  size_t base_len;
+		  size_t len = strlen (name);
+		  versioned_name = bfd_alloc (flinfo->output_bfd, len);
+		  if (versioned_name == NULL)
+		    return 0;
+		  base_len = base_end - name;
+		  memcpy (versioned_name, name, base_len);
+		  memcpy (versioned_name + base_len, version,
+			  len - base_len);
+		}
+	    }
+	}
+      else if (flinfo->info->unique_symbol
+	       && ELF_ST_BIND (elfsym->st_info) == STB_LOCAL)
+	{
+	  struct local_hash_entry *lh;
+	  switch (ELF_ST_TYPE (elfsym->st_info))
+	    {
+	    case STT_FILE:
+	    case STT_SECTION:
+	      break;
+	    default:
+	      lh = (struct local_hash_entry *) bfd_hash_lookup
+		     (&flinfo->local_hash_table, name, TRUE, FALSE);
+	      if (lh == NULL)
 		return 0;
-	      base_len = base_end - name;
-	      memcpy (versioned_name, name, base_len);
-	      memcpy (versioned_name + base_len, version,
-		      len - base_len);
+	      if (lh->count)
+		{
+		  /* Append ".COUNT" to duplicated local symbols.  */
+		  size_t count_len;
+		  size_t base_len = lh->size;
+		  char buf[30];
+		  sprintf (buf, "%lx", lh->count);
+		  if (!base_len)
+		    {
+		      base_len = strlen (name);
+		      lh->size = base_len;
+		    }
+		  count_len = strlen (buf);
+		  versioned_name = bfd_alloc (flinfo->output_bfd,
+					      base_len + count_len + 2);
+		  if (versioned_name == NULL)
+		    return 0;
+		  memcpy (versioned_name, name, base_len);
+		  versioned_name[base_len] = '.';
+		  memcpy (versioned_name + base_len + 1, buf,
+			  count_len + 1);
+		}
+	      lh->count++;
+	      break;
 	    }
 	}
       elfsym->st_name
@@ -11996,6 +12080,7 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
   const char *std_attrs_section;
   struct elf_link_hash_table *htab = elf_hash_table (info);
   bfd_boolean sections_removed;
+  bfd_boolean ret;
 
   if (!is_elf_hash_table (htab))
     return FALSE;
@@ -12009,6 +12094,7 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
   emit_relocs = (bfd_link_relocatable (info)
 		 || info->emitrelocations);
 
+  memset (&flinfo, 0, sizeof (flinfo));
   flinfo.info = info;
   flinfo.output_bfd = abfd;
   flinfo.symstrtab = _bfd_elf_strtab_init ();
@@ -12028,16 +12114,11 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
       /* Note that it is OK if symver_sec is NULL.  */
     }
 
-  flinfo.contents = NULL;
-  flinfo.external_relocs = NULL;
-  flinfo.internal_relocs = NULL;
-  flinfo.external_syms = NULL;
-  flinfo.locsym_shndx = NULL;
-  flinfo.internal_syms = NULL;
-  flinfo.indices = NULL;
-  flinfo.sections = NULL;
-  flinfo.symshndxbuf = NULL;
-  flinfo.filesym_count = 0;
+  if (info->unique_symbol
+      && !bfd_hash_table_init (&flinfo.local_hash_table,
+			       local_hash_newfunc,
+			       sizeof (struct local_hash_entry)))
+    return FALSE;
 
   /* The object attributes have been merged.  Remove the input
      sections from the link, and set the contents of the output
@@ -12572,6 +12653,8 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
 	  }
     }
 
+  ret = TRUE;
+
   /* Output any global symbols that got converted to local in a
      version script or due to symbol visibility.  We do this in a
      separate step since ELF requires all local symbols to appear
@@ -12584,7 +12667,10 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
   eoinfo.file_sym_done = FALSE;
   bfd_hash_traverse (&info->hash->table, elf_link_output_extsym, &eoinfo);
   if (eoinfo.failed)
-    return FALSE;
+    {
+      ret = FALSE;
+      goto return_local_hash_table;
+    }
 
   /* If backend needs to output some local symbols not present in the hash
      table, do it now.  */
@@ -12598,7 +12684,10 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
       if (! ((*bed->elf_backend_output_arch_local_syms)
 	     (abfd, info, &flinfo,
 	      (out_sym_func) elf_link_output_symstrtab)))
-	return FALSE;
+	{
+	  ret = FALSE;
+	  goto return_local_hash_table;
+	}
     }
 
   /* That wrote out all the local symbols.  Finish up the symbol table
@@ -12645,7 +12734,10 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
 	      BFD_ASSERT (indx > 0);
 	      sym.st_shndx = indx;
 	      if (! check_dynsym (abfd, &sym))
-		return FALSE;
+		{
+		  ret = FALSE;
+		  goto return_local_hash_table;
+		}
 	      sym.st_value = s->vma;
 	      dest = dynsym + dynindx * bed->s->sizeof_sym;
 	      bed->s->swap_symbol_out (abfd, &sym, dest, 0);
@@ -12677,7 +12769,10 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
 		  sym.st_shndx =
 		    elf_section_data (s->output_section)->this_idx;
 		  if (! check_dynsym (abfd, &sym))
-		    return FALSE;
+		    {
+		      ret = FALSE;
+		      goto return_local_hash_table;
+		    }
 		  sym.st_value = (s->output_section->vma
 				  + s->output_offset
 				  + e->isym.st_value);
@@ -12695,7 +12790,10 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
   eoinfo.flinfo = &flinfo;
   bfd_hash_traverse (&info->hash->table, elf_link_output_extsym, &eoinfo);
   if (eoinfo.failed)
-    return FALSE;
+    {
+      ret = FALSE;
+      goto return_local_hash_table;
+    }
 
   /* If backend needs to output some symbols not present in the hash
      table, do it now.  */
@@ -12709,7 +12807,10 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
       if (! ((*bed->elf_backend_output_arch_syms)
 	     (abfd, info, &flinfo,
 	      (out_sym_func) elf_link_output_symstrtab)))
-	return FALSE;
+	{
+	  ret = FALSE;
+	  goto return_local_hash_table;
+	}
     }
 
   /* Finalize the .strtab section.  */
@@ -12717,7 +12818,10 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
 
   /* Swap out the .strtab section. */
   if (!elf_link_swap_symbols_out (&flinfo))
-    return FALSE;
+    {
+      ret = FALSE;
+      goto return_local_hash_table;
+    }
 
   /* Now we know the size of the symtab section.  */
   if (bfd_get_symcount (abfd) > 0)
@@ -12744,7 +12848,10 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
 
 	      if (bfd_seek (abfd, symtab_shndx_hdr->sh_offset, SEEK_SET) != 0
 		  || (bfd_bwrite (flinfo.symshndxbuf, amt, abfd) != amt))
-		return FALSE;
+		{
+		  ret = FALSE;
+		  goto return_local_hash_table;
+		}
 	    }
 	}
 
@@ -12766,14 +12873,18 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
 
       if (bfd_seek (abfd, symstrtab_hdr->sh_offset, SEEK_SET) != 0
 	  || ! _bfd_elf_strtab_emit (abfd, flinfo.symstrtab))
-	return FALSE;
+	{
+	  ret = FALSE;
+	  goto return_local_hash_table;
+	}
     }
 
   if (info->out_implib_bfd && !elf_output_implib (abfd, info))
     {
       _bfd_error_handler (_("%pB: failed to generate import library"),
 			  info->out_implib_bfd);
-      return FALSE;
+      ret = FALSE;
+      goto return_local_hash_table;
     }
 
   /* Adjust the relocs to have the correct symbol indices.  */
@@ -12788,10 +12899,16 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
       sort = bed->sort_relocs_p == NULL || (*bed->sort_relocs_p) (o);
       if (esdo->rel.hdr != NULL
 	  && !elf_link_adjust_relocs (abfd, o, &esdo->rel, sort, info))
-	return FALSE;
+	{
+	  ret = FALSE;
+	  goto return_local_hash_table;
+	}
       if (esdo->rela.hdr != NULL
 	  && !elf_link_adjust_relocs (abfd, o, &esdo->rela, sort, info))
-	return FALSE;
+	{
+	  ret = FALSE;
+	  goto return_local_hash_table;
+	}
 
       /* Set the reloc_count field to 0 to prevent write_relocs from
 	 trying to swap the relocs out itself.  */
@@ -13110,17 +13227,25 @@ bfd_elf_final_link (bfd *abfd, struct bfd_link_info *info)
     {
       bfd_byte *contents = (bfd_byte *) bfd_malloc (attr_size);
       if (contents == NULL)
-	return FALSE;	/* Bail out and fail.  */
+	{
+	  /* Bail out and fail.  */
+	  ret = FALSE;
+	  goto return_local_hash_table;
+	}
       bfd_elf_set_obj_attr_contents (abfd, contents, attr_size);
       bfd_set_section_contents (abfd, attr_section, contents, 0, attr_size);
       free (contents);
     }
 
-  return TRUE;
+ return_local_hash_table:
+  if (info->unique_symbol)
+    bfd_hash_table_free (&flinfo.local_hash_table);
+  return ret;
 
  error_return:
   elf_final_link_free (abfd, &flinfo);
-  return FALSE;
+  ret = FALSE;
+  goto return_local_hash_table;
 }
 
 /* Initialize COOKIE for input bfd ABFD.  */