Dynamic TLS section symbols

It is possible to create shared libraries on PowerPC using
-ftls-model=inital-exec or -ftls-model=local-exec.  The first is half
reasonable, getting you a shared library that can't be dlopen'd but
otherwise is reasonable.  The second is quite bad.  Not only do you
lose being able to dlopen, the library also has dynamic text
relocations.  Worse, the TPREL16_LO, TPREL16_HA and other TPREL16
dynamic relocs emitted were wrong, resulting in wrong values being
applied by ld.so.

Using the first TLS section symbol in dynamic relocations for local
TLS symbols doesn't work.  It's wrong because TLS symbols used by TLS
relocs have values relative to the TLS segment, whereas the TLS
section symbols are addresses.  This patch instead uses a symbol index
of zero which is used elsewhere by PowerPC on dynamic TLS relocs.
It's not strictly ABI compliant to use a non-TLS symbol with TLS
relocs but symbol index zero can be interpreted as "no symbol".  Not
using the first TLS section symbol means it doesn't need to be dynamic.

The patch also fixes a further problem with PowerPC32 dynamic TPREL16*
relocs, which shouldn't have the symbol value in the addend as we do
for non-TLS symbols.

bfd/
	* elflink.c (_bfd_elf_omit_section_dynsym_default): Don't keep
	tls_sec.
	(_bfd_elf_init_1_index_section): Prefer not using TLS sections.
	(_bfd_elf_init_2_index_sections): Likewise.
	* elf64-ppc.c (ppc64_elf_relocate_section): When emitting dynamic
	relocations for local TLS symbols, use STN_UNDEF as the relocation
	symbol.
	* elf32-ppc.c (ppc_elf_relocate_section): Likewise, and don't
	leave TLS symbol value in the addend.
ld/
	* testsuite/ld-powerpc/tlsso.r: Update.
	* testsuite/ld-powerpc/tlsso32.g: Update.
	* testsuite/ld-powerpc/tlsso32.r: Update.
	* testsuite/ld-powerpc/tlstocso.r: Update.
	* testsuite/ld-cris/tls-dso-dtpoffd2.d: Update.
	* testsuite/ld-cris/tls-dso-dtpoffd4.d: Update.
	* testsuite/ld-cris/tls-dso-tpoffgotcomm1.d: Update.
	* testsuite/ld-cris/tls-gd-1.d: Update.
	* testsuite/ld-cris/tls-gd-1h.d: Update.
	* testsuite/ld-cris/tls-gd-2.d: Update.
	* testsuite/ld-cris/tls-gd-2h.d: Update.
	* testsuite/ld-cris/tls-ie-10.d: Update.
	* testsuite/ld-cris/tls-ie-11.d: Update.
	* testsuite/ld-cris/tls-ie-8.d: Update.
	* testsuite/ld-cris/tls-ie-9.d: Update.
	* testsuite/ld-cris/tls-js1.d: Update.
	* testsuite/ld-cris/tls-ld-4.d: Update.
	* testsuite/ld-cris/tls-ld-5.d: Update.
	* testsuite/ld-cris/tls-ld-6.d: Update.
	* testsuite/ld-cris/tls-ld-7.d: Update.
	* testsuite/ld-cris/tls-ldgd-14.d: Update.
	* testsuite/ld-cris/tls-ldgd-15.d: Update.
	* testsuite/ld-cris/tls-ldgdx-14.d: Update.
	* testsuite/ld-cris/tls-ldgdx-15.d: Update.
	* testsuite/ld-cris/tls-local-54.d: Update.
	* testsuite/ld-cris/tls-local-60.d: Update.
	* testsuite/ld-cris/tls-local-61.d: Update.
	* testsuite/ld-cris/tls-local-63.d: Update.
	* testsuite/ld-cris/tls-local-64.d: Update.
	* testsuite/ld-cris/tls-ok-30.d: Update.
	* testsuite/ld-cris/tls-ok-32.d: Update.
	* testsuite/ld-cris/tls-ok-34.d: Update.
	* testsuite/ld-mips-elf/tls-multi-got-1.got: Update.
	* testsuite/ld-mips-elf/tls-multi-got-1.r: Update.
	* testsuite/ld-mips-elf/tlsdyn-pie-o32.d: Update.
	* testsuite/ld-mips-elf/tlsdyn-pie-o32.got: Update.
	* testsuite/ld-mips-elf/tlslib-o32-hidden.got: Update.
	* testsuite/ld-mips-elf/tlslib-o32-ver.got: Update.
	* testsuite/ld-mips-elf/tlslib-o32.got: Update.
	* testsuite/ld-s390/tlspic.rd: Update.
	* testsuite/ld-s390/tlspic_64.rd: Update.
	* testsuite/ld-sparc/tlssunnopic32.rd: Update.
	* testsuite/ld-sparc/tlssunnopic64.rd: Update.
	* testsuite/ld-sparc/tlssunpic32.rd: Update.
	* testsuite/ld-sparc/tlssunpic64.rd: Update.

4 files changed, 74 insertions, 36 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 7daec6b..b41c059 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,15 @@
+2019-07-13  Alan Modra  <amodra@gmail.com>
+
+	* elflink.c (_bfd_elf_omit_section_dynsym_default): Don't keep
+	tls_sec.
+	(_bfd_elf_init_1_index_section): Prefer not using TLS sections.
+	(_bfd_elf_init_2_index_sections): Likewise.
+	* elf64-ppc.c (ppc64_elf_relocate_section): When emitting dynamic
+	relocations for local TLS symbols, use STN_UNDEF as the relocation
+	symbol.
+	* elf32-ppc.c (ppc_elf_relocate_section): Likewise, and don't
+	leave TLS symbol value in the addend.
+
 2019-07-08  Alan Modra  <amodra@gmail.com>
 
 	PR 24785
diff --git a/bfd/elf32-ppc.c b/bfd/elf32-ppc.c
index ae03d72..33ab4e0 100644
--- a/bfd/elf32-ppc.c
+++ b/bfd/elf32-ppc.c
@@ -8209,19 +8209,27 @@ ppc_elf_relocate_section (bfd *output_bfd,
 			     but ld.so expects buggy relocs.
 			     FIXME: Why not always use a zero index?  */
 			  osec = sec->output_section;
-			  indx = elf_section_data (osec)->dynindx;
-			  if (indx == 0)
+			  if ((osec->flags & SEC_THREAD_LOCAL) != 0)
+			    {
+			      osec = htab->elf.tls_sec;
+			      indx = 0;
+			    }
+			  else
 			    {
-			      osec = htab->elf.text_index_section;
 			      indx = elf_section_data (osec)->dynindx;
+			      if (indx == 0)
+				{
+				  osec = htab->elf.text_index_section;
+				  indx = elf_section_data (osec)->dynindx;
+				}
+			      BFD_ASSERT (indx != 0);
 			    }
-			  BFD_ASSERT (indx != 0);
-#ifdef DEBUG
-			  if (indx == 0)
-			    printf ("indx=%ld section=%s flags=%08x name=%s\n",
-				    indx, osec->name, osec->flags,
-				    h->root.root.string);
-#endif
+
+			  /* ld.so doesn't expect buggy TLS relocs.
+			     Don't leave the symbol value in the
+			     addend for them.  */
+			  if (IS_PPC_TLS_RELOC (r_type))
+			    outrel.r_addend -= osec->vma;
 			}
 
 		      outrel.r_info = ELF32_R_INFO (indx, r_type);
diff --git a/bfd/elf64-ppc.c b/bfd/elf64-ppc.c
index c5c18d0..d77cfdf 100644
--- a/bfd/elf64-ppc.c
+++ b/bfd/elf64-ppc.c
@@ -15891,21 +15891,38 @@ ppc64_elf_relocate_section (bfd *output_bfd,
 			}
 		      else
 			{
-			  asection *osec;
+			  asection *osec = sec->output_section;
 
-			  osec = sec->output_section;
-			  indx = elf_section_data (osec)->dynindx;
-
-			  if (indx == 0)
+			  if ((osec->flags & SEC_THREAD_LOCAL) != 0)
+			    {
+			      /* TLS symbol values are relative to the
+				 TLS segment.  Dynamic relocations for
+				 local TLS symbols therefore can't be
+				 reduced to a relocation against their
+				 section symbol because it holds the
+				 address of the section, not a value
+				 relative to the TLS segment.  We could
+				 change the .tdata dynamic section symbol
+				 to be zero value but STN_UNDEF works
+				 and is used elsewhere, eg. for TPREL64
+				 GOT relocs against local TLS symbols.  */
+			      osec = htab->elf.tls_sec;
+			      indx = 0;
+			    }
+			  else
 			    {
-			      if ((osec->flags & SEC_READONLY) == 0
-				  && htab->elf.data_index_section != NULL)
-				osec = htab->elf.data_index_section;
-			      else
-				osec = htab->elf.text_index_section;
 			      indx = elf_section_data (osec)->dynindx;
+			      if (indx == 0)
+				{
+				  if ((osec->flags & SEC_READONLY) == 0
+				      && htab->elf.data_index_section != NULL)
+				    osec = htab->elf.data_index_section;
+				  else
+				    osec = htab->elf.text_index_section;
+				  indx = elf_section_data (osec)->dynindx;
+				}
+			      BFD_ASSERT (indx != 0);
 			    }
-			  BFD_ASSERT (indx != 0);
 
 			  /* We are turning this relocation into one
 			     against a section symbol, so subtract out
diff --git a/bfd/elflink.c b/bfd/elflink.c
index 02ea2dc..d146a4b 100644
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -900,9 +900,6 @@ _bfd_elf_omit_section_dynsym_default (bfd *output_bfd ATTRIBUTE_UNUSED,
 	 SHT_PROGBITS/SHT_NOBITS.  */
     case SHT_NULL:
       htab = elf_hash_table (info);
-      if (p == htab->tls_sec)
-	return FALSE;
-
       if (htab->text_index_section != NULL)
 	return p != htab->text_index_section && p != htab->data_index_section;
 
@@ -7052,14 +7049,17 @@ void
 _bfd_elf_init_1_index_section (bfd *output_bfd, struct bfd_link_info *info)
 {
   asection *s;
+  asection *found = NULL;
 
   for (s = output_bfd->sections; s != NULL; s = s->next)
     if ((s->flags & (SEC_EXCLUDE | SEC_ALLOC)) == SEC_ALLOC
 	&& !_bfd_elf_omit_section_dynsym_default (output_bfd, info, s))
       {
-	elf_hash_table (info)->text_index_section = s;
-	break;
+	found = s;
+	if ((s->flags & SEC_THREAD_LOCAL) == 0)
+	  break;
       }
+  elf_hash_table (info)->text_index_section = found;
 }
 
 /* Find two non-excluded output sections, one for code, one for data.
@@ -7068,29 +7068,30 @@ void
 _bfd_elf_init_2_index_sections (bfd *output_bfd, struct bfd_link_info *info)
 {
   asection *s;
+  asection *found = NULL;
 
   /* Data first, since setting text_index_section changes
      _bfd_elf_omit_section_dynsym_default.  */
   for (s = output_bfd->sections; s != NULL; s = s->next)
-    if (((s->flags & (SEC_EXCLUDE | SEC_ALLOC | SEC_READONLY)) == SEC_ALLOC)
+    if ((s->flags & (SEC_EXCLUDE | SEC_ALLOC)) == SEC_ALLOC
+	&& !(s->flags & SEC_READONLY)
 	&& !_bfd_elf_omit_section_dynsym_default (output_bfd, info, s))
       {
-	elf_hash_table (info)->data_index_section = s;
-	break;
+	found = s;
+	if ((s->flags & SEC_THREAD_LOCAL) == 0)
+	  break;
       }
+  elf_hash_table (info)->data_index_section = found;
 
   for (s = output_bfd->sections; s != NULL; s = s->next)
-    if (((s->flags & (SEC_EXCLUDE | SEC_ALLOC | SEC_READONLY))
-	 == (SEC_ALLOC | SEC_READONLY))
+    if ((s->flags & (SEC_EXCLUDE | SEC_ALLOC)) == SEC_ALLOC
+	&& (s->flags & SEC_READONLY)
 	&& !_bfd_elf_omit_section_dynsym_default (output_bfd, info, s))
       {
-	elf_hash_table (info)->text_index_section = s;
+	found = s;
 	break;
       }
-
-  if (elf_hash_table (info)->text_index_section == NULL)
-    elf_hash_table (info)->text_index_section
-      = elf_hash_table (info)->data_index_section;
+  elf_hash_table (info)->text_index_section = found;
 }
 
 bfd_boolean