Add support for a MIPS specific .MIPS.xhash section.

  This patch is a reimplementation of [1] which was submitted in 2015 by
Neil Schellenberger. Copyright issue was sorted out [2] last year.
It proposed a new section (.gnu.xhash) and related dynamic tag
(DT_GNU_XHASH). The new section would be virtually identical to the
existing .gnu.hash except for the translation table (xlat) which would
contain correct MIPS .dynsym indexes corresponding to the hashvals in
chains. This is because MIPS ABI imposes a different ordering on the
dynsyms than the one expected by the .gnu.hash section. Another addition
would be a leading word (ngnusyms) which would contain the number of
entries in the translation table.

  In this patch, the new section name and dynamic tag are changed to
reflect the fact that the section should be treated as MIPS-specific
(.MIPS.xhash and DT_MIPS_XHASH).

  This patch addresses the alignment issue as reported in [3], which is
caused by the leading word added to the .MIPS.xhash section. Leading word
is removed in this patch, and the number of entries in the translation
table is now calculated using DT_MIPS_SYMTABNO dynamic tag (this is
addressed by the corresponding glibc patch).

  Suggestions on coding style in [4] were taken into account. Existing
GNU hash testcase was covered, and another one was added in the MIPS
part of the testsuite.

  The other major change is reserving MIPS ABI version 5 for .MIPS.xhash,
marking the need of support for .MIPS.xhash in the dynamic linker (again,
addressed in the corresponding glibc patch). This is something which I
am not sure of, especially after reading [5]. I am confused on whether
this ABI version is reserved for IFUNC, or it can be used for this
purpose.

Already mentioned glibc patch is submitted at:
https://sourceware.org/ml/libc-alpha/2019-06/msg00456.html

[1] https://sourceware.org/ml/binutils/2015-10/msg00057.html
[2] https://sourceware.org/ml/binutils/2018-03/msg00025.html
[3] https://sourceware.org/ml/binutils/2016-01/msg00006.html
[4] https://sourceware.org/ml/binutils/2016-02/msg00097.html
[5] https://sourceware.org/ml/libc-alpha/2016-12/msg00853.html

ld      * emulparams/elf32bmip.sh: Add .MIPS.xhash section.
        * emulparams/elf32bmipn32-defs.sh: Add .MIPS.xhash section.
        * emulparams/elf64bmip-defs.sh: Add .MIPS.xhash section.
        * emultempl/mipself.em: Remove mips_after_parse function.
        * testsuite/ld-elf/hash.d: Update comment.
        * testsuite/ld-mips-elf/hash1.d: New test.
        * testsuite/ld-mips-elf/hash1.s: Ditto.
        * testsuite/ld-mips-elf/hash1a.d: Remove.
        * testsuite/ld-mips-elf/hash1b.d: Ditto.
        * testsuite/ld-mips-elf/hash1c.d: Ditto
        * testsuite/ld-mips-elf/hash2.d: New test.
        * testsuite/ld-mips-elf/mips-elf.exp: New tests.
        * testsuite/ld-mips-elf/start.s: New test.

bfd     * elf-bfd.h (struct elf_backend_data): New members.
        * elflink.c (_bfd_elf_link_create_dynamic_sections): Create
        .gnu.hash section if necessary.
        (struct collect_gnu_hash_codes): New member.
        (elf_gnu_hash_process_symidx): New function name.
        (elf_renumber_gnu_hash_syms): Ignore local and undefined
        symbols. Record xlat location for every symbol which should have
        a .MIPS.xhash entry.
        (bfd_elf_size_dynamic_sections): Add DT_GNU_HASH dynamic tag to
        dynamic section if necessary.
        (GNU_HASH_SECTION_NAME): New define.
        (bfd_elf_size_dynsym_hash_dynstr): Get .MIPS.xhash section.
        Update the section size info.
        * elfxx-mips.c (struct mips_elf_hash_sort_data): New members.
        (struct mips_elf_link_hash_entry): New member.
        (mips_elf_link_hash_newfunc): Initialize .MIPS.xhash translation
        table location.
        (mips_elf_sort_hash_table): Initialize the pointer to the
        .MIPS.xhash section.
        (mips_elf_sort_hash_table_f): Populate the .MIPS.xhash
        translation table entry with the symbol dynindx.
        (_bfd_mips_elf_section_from_shdr): Add SHT_MIPS_XHASH.
        (_bfd_mips_elf_fake_sections): Initialize .MIPS.xhash section
        info.
        (_bfd_mips_elf_create_dynamic_sections): Create .MIPS.xhash
        section.
        (_bfd_mips_elf_size_dynamic_sections): Add DT_MIPS_XHASH tag to
        dynamic section.
        (_bfd_mips_elf_finish_synamic_sections): Add DT_MIPS_XHASH.
        (_bfd_mips_elf_final_write_processing): Set .MIPS.xhash section
        sh_link info.
        (_bfd_mips_elf_get_target_dtag): Get DT_MIPS_XHASH tag.
        (MIPS_LIBC_ABI_XHASH): New ABI version enum value.
        (_bfd_mips_post_process_headers): Mark the ABI version as
        MIPS_LIBC_ABI_XHASH if there exists a .MIPS.xhash section,
        but not a .hash section.
        (_bfd_mips_elf_record_xhash_symbol): New function. Record a
        position in the translation table, associated with the hash
        entry.
        * elfxx-mips.h (literal_reloc_p): Define
        elf_backend_record_xhash_symbol backend hook.
        * elfxx-target.h: Initialize elf_backend_record_xhash_symbol
        backend hook.

include * elf/mips.h (SHT_GNU_XHASH): New define.
        (DT_GNU_XHASH): New define.

binutils * readelf.c (get_mips_dynamic_type): Return MIPS_XHASH dynamic type.
        (get_mips_section_type_name): Return MI{S_XHASH name string.
        (dynamic_section_mips_val): Initialize the .MIPS.xhash dynamic
        info.
        (process_symbol_table): Initialize the .MIPS.xhash section
        pointer. Adjust the readelf output to support the new section.
        (process_object): Set the .MIPS.xhash dynamic info to zero.

1 files changed, 78 insertions, 0 deletions

diff --git a/bfd/elfxx-mips.c b/bfd/elfxx-mips.c
index 8e577b2..e845c90 100644
--- a/bfd/elfxx-mips.c
+++ b/bfd/elfxx-mips.c
@@ -322,6 +322,11 @@ struct mips_elf_hash_sort_data
   /* The greatest dynamic symbol table index corresponding to an external
      symbol without a GOT entry.  */
   bfd_size_type max_non_got_dynindx;
+  /* If non-NULL, output BFD for .MIPS.xhash finalization.  */
+  bfd *output_bfd;
+  /* If non-NULL, pointer to contents of .MIPS.xhash for filling in
+     real final dynindx.  */
+  bfd_byte *mipsxhash;
 };
 
 /* We make up to two PLT entries if needed, one for standard MIPS code
@@ -379,6 +384,9 @@ struct mips_elf_link_hash_entry
      being called returns a floating point value.  */
   asection *call_fp_stub;
 
+  /* If non-zero, location in .MIPS.xhash to write real final dynindx.  */
+  bfd_vma mipsxhash_loc;
+
   /* The highest GGA_* value that satisfies all references to this symbol.  */
   unsigned int global_got_area : 2;
 
@@ -1335,6 +1343,7 @@ mips_elf_link_hash_newfunc (struct bfd_hash_entry *entry,
       ret->fn_stub = NULL;
       ret->call_stub = NULL;
       ret->call_fp_stub = NULL;
+      ret->mipsxhash_loc = 0;
       ret->global_got_area = GGA_NONE;
       ret->got_only_for_calls = TRUE;
       ret->readonly_reloc = FALSE;
@@ -3907,6 +3916,18 @@ mips_elf_sort_hash_table (bfd *abfd, struct bfd_link_info *info)
      at the head of the table; see `_bfd_elf_link_renumber_dynsyms'.  */
   hsd.max_local_dynindx = count_section_dynsyms (abfd, info) + 1;
   hsd.max_non_got_dynindx = htab->root.local_dynsymcount + 1;
+  hsd.output_bfd = abfd;
+  if (htab->root.dynobj != NULL
+      && htab->root.dynamic_sections_created
+      && info->emit_gnu_hash)
+    {
+      asection *s = bfd_get_linker_section (htab->root.dynobj, ".MIPS.xhash");
+      BFD_ASSERT (s != NULL);
+      hsd.mipsxhash = s->contents;
+      BFD_ASSERT (hsd.mipsxhash != NULL);
+    }
+  else
+    hsd.mipsxhash = NULL;
   mips_elf_link_hash_traverse (htab, mips_elf_sort_hash_table_f, &hsd);
 
   /* There should have been enough room in the symbol table to
@@ -3958,6 +3979,12 @@ mips_elf_sort_hash_table_f (struct mips_elf_link_hash_entry *h, void *data)
       break;
     }
 
+  /* Populate the .MIPS.xhash translation table entry with
+     the symbol dynindx.  */
+  if (h->mipsxhash_loc != 0 && hsd->mipsxhash != NULL)
+    bfd_put_32 (hsd->output_bfd, h->root.dynindx,
+		hsd->mipsxhash + h->mipsxhash_loc);
+
   return TRUE;
 }
 
@@ -7475,6 +7502,9 @@ _bfd_mips_elf_section_from_shdr (bfd *abfd,
 	  && ! CONST_STRNEQ (name, ".MIPS.post_rel"))
 	return FALSE;
       break;
+    case SHT_MIPS_XHASH:
+      if (strcmp (name, ".MIPS.xhash") != 0)
+	return FALSE;
     default:
       break;
     }
@@ -7708,6 +7738,12 @@ _bfd_mips_elf_fake_sections (bfd *abfd, Elf_Internal_Shdr *hdr, asection *sec)
       hdr->sh_flags |= SHF_ALLOC;
       hdr->sh_entsize = 8;
     }
+  else if (strcmp (name, ".MIPS.xhash") == 0)
+    {
+      hdr->sh_type = SHT_MIPS_XHASH;
+      hdr->sh_flags |= SHF_ALLOC;
+      hdr->sh_entsize = get_elf_backend_data(abfd)->s->arch_size == 64 ? 0 : 4;
+    }
 
   /* The generic elf_fake_sections will set up REL_HDR using the default
    kind of relocations.  We used to set up a second header for the
@@ -7994,6 +8030,11 @@ _bfd_mips_elf_create_dynamic_sections (bfd *abfd, struct bfd_link_info *info)
 	return FALSE;
     }
 
+  /* Create .MIPS.xhash section.  */
+  if (info->emit_gnu_hash)
+    s = bfd_make_section_anyway_with_flags (abfd, ".MIPS.xhash",
+					    flags | SEC_READONLY);
+
   /* On IRIX5, we adjust add some additional symbols and change the
      alignments of several sections.  There is no ABI documentation
      indicating that this is necessary on IRIX6, nor any evidence that
@@ -10176,6 +10217,10 @@ _bfd_mips_elf_size_dynamic_sections (bfd *output_bfd,
 	  if (! MIPS_ELF_ADD_DYNAMIC_ENTRY (info, DT_MIPS_GOTSYM, 0))
 	    return FALSE;
 
+	  if (info->emit_gnu_hash
+	      && ! MIPS_ELF_ADD_DYNAMIC_ENTRY (info, DT_MIPS_XHASH, 0))
+	    return FALSE;
+
 	  if (IRIX_COMPAT (dynobj) == ict_irix5
 	      && ! MIPS_ELF_ADD_DYNAMIC_ENTRY (info, DT_MIPS_HIPAGENO, 0))
 	    return FALSE;
@@ -11953,6 +11998,12 @@ _bfd_mips_elf_finish_dynamic_sections (bfd *output_bfd,
 		swap_out_p = FALSE;
 	      break;
 
+	    case DT_MIPS_XHASH:
+	      name = ".MIPS.xhash";
+	      s = bfd_get_linker_section (dynobj, name);
+	      dyn.d_un.d_ptr = s->output_section->vma + s->output_offset;
+	      break;
+
 	    default:
 	      swap_out_p = FALSE;
 	      if (htab->is_vxworks
@@ -12440,6 +12491,10 @@ _bfd_mips_final_write_processing (bfd *abfd)
 	  (*hdrpp)->sh_link = elf_section_data (sec)->this_idx;
 	  break;
 
+	case SHT_MIPS_XHASH:
+	  sec = bfd_get_section_by_name (abfd, ".dynsym");
+	  if (sec != NULL)
+	    (*hdrpp)->sh_link = elf_section_data (sec)->this_idx;
 	}
     }
 }
@@ -15943,6 +15998,8 @@ _bfd_mips_elf_get_target_dtag (bfd_vma dtag)
       return "DT_MIPS_PLTGOT";
     case DT_MIPS_RWPLT:
       return "DT_MIPS_RWPLT";
+    case DT_MIPS_XHASH:
+      return "DT_MIPS_XHASH";
     }
 }
 
@@ -16276,6 +16333,7 @@ const struct bfd_elf_special_section _bfd_mips_elf_special_sections[] =
   { STRING_COMMA_LEN (".sbss"),	 -2, SHT_NOBITS,     SHF_ALLOC + SHF_WRITE + SHF_MIPS_GPREL },
   { STRING_COMMA_LEN (".sdata"), -2, SHT_PROGBITS,   SHF_ALLOC + SHF_WRITE + SHF_MIPS_GPREL },
   { STRING_COMMA_LEN (".ucode"),  0, SHT_MIPS_UCODE, 0 },
+  { STRING_COMMA_LEN (".MIPS.xhash"),  0, SHT_MIPS_XHASH,   SHF_ALLOC },
   { NULL,		      0,  0, 0,		     0 }
 };
 
@@ -16590,6 +16648,7 @@ enum
   MIPS_LIBC_ABI_UNIQUE,
   MIPS_LIBC_ABI_MIPS_O32_FP64,
   MIPS_LIBC_ABI_ABSOLUTE,
+  MIPS_LIBC_ABI_XHASH,
   MIPS_LIBC_ABI_MAX
 };
 
@@ -16617,6 +16676,11 @@ _bfd_mips_post_process_headers (bfd *abfd, struct bfd_link_info *link_info)
   if (htab != NULL && htab->use_absolute_zero && htab->gnu_target)
     i_ehdrp->e_ident[EI_ABIVERSION] = MIPS_LIBC_ABI_ABSOLUTE;
 
+  /* Mark that we need support for .MIPS.xhash in the dynamic linker,
+     if it is the only hash section that will be created.  */
+  if (link_info && link_info->emit_gnu_hash && !link_info->emit_hash)
+    i_ehdrp->e_ident[EI_ABIVERSION] = MIPS_LIBC_ABI_XHASH;
+
   _bfd_elf_post_process_headers (abfd, link_info);
 }
 
@@ -16635,3 +16699,17 @@ _bfd_mips_elf_cant_unwind_opcode
 {
   return COMPACT_EH_CANT_UNWIND_OPCODE;
 }
+
+/* Record a position XLAT_LOC in the xlat translation table, associated with
+   the hash entry H.  The entry in the translation table will later be
+   populated with the real symbol dynindx.  */
+
+void
+_bfd_mips_elf_record_xhash_symbol (struct elf_link_hash_entry *h,
+				   bfd_vma xlat_loc)
+{
+  struct mips_elf_link_hash_entry *hmips;
+
+  hmips = (struct mips_elf_link_hash_entry *) h;
+  hmips->mipsxhash_loc = xlat_loc;
+}