2016-08-04 Thomas Preud'homme <thomas.preudhomme@arm.com>

bfd/
	* elf32-arm.c (CMSE_PREFIX): Define macro.
	(elf32_arm_stub_cmse_branch_thumb_only): Define stub sequence.
	(cmse_branch_thumb_only): Declare stub.
	(struct elf32_arm_link_hash_table): Define cmse_stub_sec field.
	(elf32_arm_get_plt_info): Add globals parameter.  Use it to return
	FALSE if there is no PLT.
	(arm_type_of_stub): Adapt to new elf32_arm_get_plt_info signature.
	(elf32_arm_final_link_relocate): Likewise.
	(elf32_arm_gc_sweep_hook): Likewise.
	(elf32_arm_gc_mark_extra_sections): Mark sections holding ARMv8-M
	secure entry functions.
	(arm_stub_is_thumb): Add case for arm_stub_cmse_branch_thumb_only.
	(arm_dedicated_stub_output_section_required): Change to a switch case
	and add a case for arm_stub_cmse_branch_thumb_only.
	(arm_dedicated_stub_output_section_required_alignment): Likewise.
	(arm_stub_dedicated_output_section_name): Likewise.
	(arm_stub_dedicated_input_section_ptr): Likewise and remove
	ATTRIBUTE_UNUSED for htab parameter.
	(arm_stub_required_alignment): Likewise.
	(arm_stub_sym_claimed): Likewise.
	(arm_dedicated_stub_section_padding): Likewise.
	(cmse_scan): New function.
	(elf32_arm_size_stubs): Call cmse_scan for ARM M profile targets.
	Set stub_changed to TRUE if such veneers were created.
	(elf32_arm_swap_symbol_in): Add detection code for CMSE special
	symbols.

include/
	* arm.h (ARM_GET_SYM_CMSE_SPCL): Define macro.
	(ARM_SET_SYM_CMSE_SPCL): Likewise.

ld/
	* ld.texinfo (Placement of SG veneers): New concept entry.
	* testsuite/ld-arm/arm-elf.exp
	(Secure gateway veneers: no .gnu.sgstubs section): New test.
	(Secure gateway veneers: wrong entry functions): Likewise.
	(Secure gateway veneers (ARMv8-M Baseline)): Likewise.
	(Secure gateway veneers (ARMv8-M Mainline)): Likewise.
	* testsuite/ld-arm/cmse-veneers.s: New file.
	* testsuite/ld-arm/cmse-veneers.d: Likewise.
	* testsuite/ld-arm/cmse-veneers.rd: Likewise.
	* testsuite/ld-arm/cmse-veneers.sd: Likewise.
	* testsuite/ld-arm/cmse-veneers-no-gnu_sgstubs.out: Likewise.
	* testsuite/ld-arm/cmse-veneers-wrong-entryfct.out: Likewise.

13 files changed, 608 insertions, 20 deletions

diff --git a/bfd/ChangeLog b/bfd/ChangeLog
index 753df715ef6..312bfae8957 100644
--- a/bfd/ChangeLog
+++ b/bfd/ChangeLog
@@ -1,3 +1,32 @@
+2016-08-04  Thomas Preud'homme  <thomas.preudhomme@arm.com>
+
+	* elf32-arm.c (CMSE_PREFIX): Define macro.
+	(elf32_arm_stub_cmse_branch_thumb_only): Define stub sequence.
+	(cmse_branch_thumb_only): Declare stub.
+	(struct elf32_arm_link_hash_table): Define cmse_stub_sec field.
+	(elf32_arm_get_plt_info): Add globals parameter.  Use it to return
+	FALSE if there is no PLT.
+	(arm_type_of_stub): Adapt to new elf32_arm_get_plt_info signature.
+	(elf32_arm_final_link_relocate): Likewise.
+	(elf32_arm_gc_sweep_hook): Likewise.
+	(elf32_arm_gc_mark_extra_sections): Mark sections holding ARMv8-M
+	secure entry functions.
+	(arm_stub_is_thumb): Add case for arm_stub_cmse_branch_thumb_only.
+	(arm_dedicated_stub_output_section_required): Change to a switch case
+	and add a case for arm_stub_cmse_branch_thumb_only.
+	(arm_dedicated_stub_output_section_required_alignment): Likewise.
+	(arm_stub_dedicated_output_section_name): Likewise.
+	(arm_stub_dedicated_input_section_ptr): Likewise and remove
+	ATTRIBUTE_UNUSED for htab parameter.
+	(arm_stub_required_alignment): Likewise.
+	(arm_stub_sym_claimed): Likewise.
+	(arm_dedicated_stub_section_padding): Likewise.
+	(cmse_scan): New function.
+	(elf32_arm_size_stubs): Call cmse_scan for ARM M profile targets.
+	Set stub_changed to TRUE if such veneers were created.
+	(elf32_arm_swap_symbol_in): Add detection code for CMSE special
+	symbols.
+
 2016-08-02  Alan Modra  <amodra@gmail.com>
 
 	PR ld/20428
diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
index 834d6150652..10155125ce6 100644
--- a/bfd/elf32-arm.c
+++ b/bfd/elf32-arm.c
@@ -2138,6 +2138,8 @@ typedef unsigned short int insn16;
 
 #define STUB_ENTRY_NAME   "__%s_veneer"
 
+#define CMSE_PREFIX "__acle_se_"
+
 /* The name of the dynamic interpreter.  This is put in the .interp
    section.  */
 #define ELF_DYNAMIC_INTERPRETER     "/usr/lib/ld.so.1"
@@ -2561,6 +2563,13 @@ static const insn_sequence elf32_arm_stub_long_branch_arm_nacl_pic[] =
   DATA_WORD (0, R_ARM_NONE, 0),         /* .word 0 */
 };
 
+/* Stub used for transition to secure state (aka SG veneer).  */
+static const insn_sequence elf32_arm_stub_cmse_branch_thumb_only[] =
+{
+  THUMB32_INSN (0xe97fe97f),		/* sg.  */
+  THUMB32_B_INSN (0xf000b800, -4),	/* b.w original_branch_dest.  */
+};
+
 
 /* Cortex-A8 erratum-workaround stubs.  */
 
@@ -2640,6 +2649,7 @@ static const insn_sequence elf32_arm_stub_a8_veneer_blx[] =
   DEF_STUB(long_branch_v4t_thumb_tls_pic) \
   DEF_STUB(long_branch_arm_nacl) \
   DEF_STUB(long_branch_arm_nacl_pic) \
+  DEF_STUB(cmse_branch_thumb_only) \
   DEF_STUB(a8_veneer_b_cond) \
   DEF_STUB(a8_veneer_b) \
   DEF_STUB(a8_veneer_bl) \
@@ -3192,6 +3202,9 @@ struct elf32_arm_link_hash_table
      information on stub grouping.  */
   struct map_stub *stub_group;
 
+  /* Input stub section holding secure gateway veneers.  */
+  asection *cmse_stub_sec;
+
   /* Number of elements in stub_group.  */
   unsigned int top_id;
 
@@ -3340,12 +3353,16 @@ elf32_arm_create_local_iplt (bfd *abfd, unsigned long r_symndx)
    union and *ARM_PLT at the ARM-specific information.  */
 
 static bfd_boolean
-elf32_arm_get_plt_info (bfd *abfd, struct elf32_arm_link_hash_entry *h,
+elf32_arm_get_plt_info (bfd *abfd, struct elf32_arm_link_hash_table *globals,
+			struct elf32_arm_link_hash_entry *h,
 			unsigned long r_symndx, union gotplt_union **root_plt,
 			struct arm_plt_info **arm_plt)
 {
   struct arm_local_iplt_info *local_iplt;
 
+  if (globals->root.splt == NULL && globals->root.iplt == NULL)
+    return FALSE;
+
   if (h != NULL)
     {
       *root_plt = &h->root.plt;
@@ -3826,6 +3843,7 @@ arm_stub_is_thumb (enum elf32_arm_stub_type stub_type)
     case arm_stub_long_branch_v4t_thumb_arm_pic:
     case arm_stub_long_branch_v4t_thumb_tls_pic:
     case arm_stub_long_branch_thumb_only_pic:
+    case arm_stub_cmse_branch_thumb_only:
       return TRUE;
     case arm_stub_none:
       BFD_FAIL ();
@@ -3897,8 +3915,9 @@ arm_type_of_stub (struct bfd_link_info *info,
      the address of the appropriate trampoline.  */
   if (r_type != R_ARM_TLS_CALL
       && r_type != R_ARM_THM_TLS_CALL
-      && elf32_arm_get_plt_info (input_bfd, hash, ELF32_R_SYM (rel->r_info),
-				 &root_plt, &arm_plt)
+      && elf32_arm_get_plt_info (input_bfd, globals, hash,
+				 ELF32_R_SYM (rel->r_info), &root_plt,
+				 &arm_plt)
       && root_plt->offset != (bfd_vma) -1)
     {
       asection *splt;
@@ -4250,7 +4269,16 @@ arm_dedicated_stub_output_section_required (enum elf32_arm_stub_type stub_type)
   if (stub_type >= max_stub_type)
     abort ();  /* Should be unreachable.  */
 
-  return FALSE;
+  switch (stub_type)
+    {
+    case arm_stub_cmse_branch_thumb_only:
+      return TRUE;
+
+    default:
+      return FALSE;
+    }
+
+  abort ();  /* Should be unreachable.  */
 }
 
 /* Required alignment (as a power of 2) for the dedicated section holding
@@ -4264,8 +4292,19 @@ arm_dedicated_stub_output_section_required_alignment
   if (stub_type >= max_stub_type)
     abort ();  /* Should be unreachable.  */
 
-  BFD_ASSERT (!arm_dedicated_stub_output_section_required (stub_type));
-  return 0;
+  switch (stub_type)
+    {
+    /* Vectors of Secure Gateway veneers must be aligned on 32byte
+       boundary.  */
+    case arm_stub_cmse_branch_thumb_only:
+      return 5;
+
+    default:
+      BFD_ASSERT (!arm_dedicated_stub_output_section_required (stub_type));
+      return 0;
+    }
+
+  abort ();  /* Should be unreachable.  */
 }
 
 /* Name of the dedicated output section to put veneers of type STUB_TYPE, or
@@ -4277,8 +4316,17 @@ arm_dedicated_stub_output_section_name (enum elf32_arm_stub_type stub_type)
   if (stub_type >= max_stub_type)
     abort ();  /* Should be unreachable.  */
 
-  BFD_ASSERT (!arm_dedicated_stub_output_section_required (stub_type));
-  return NULL;
+  switch (stub_type)
+    {
+    case arm_stub_cmse_branch_thumb_only:
+      return ".gnu.sgstubs";
+
+    default:
+      BFD_ASSERT (!arm_dedicated_stub_output_section_required (stub_type));
+      return NULL;
+    }
+
+  abort ();  /* Should be unreachable.  */
 }
 
 /* If veneers of type STUB_TYPE should go in a dedicated output section,
@@ -4286,15 +4334,23 @@ arm_dedicated_stub_output_section_name (enum elf32_arm_stub_type stub_type)
    corresponding input section.  Otherwise, returns NULL.  */
 
 static asection **
-arm_dedicated_stub_input_section_ptr
-  (struct elf32_arm_link_hash_table *htab ATTRIBUTE_UNUSED,
-   enum elf32_arm_stub_type stub_type)
+arm_dedicated_stub_input_section_ptr (struct elf32_arm_link_hash_table *htab,
+				      enum elf32_arm_stub_type stub_type)
 {
   if (stub_type >= max_stub_type)
     abort ();  /* Should be unreachable.  */
 
-  BFD_ASSERT (!arm_dedicated_stub_output_section_required (stub_type));
-  return NULL;
+  switch (stub_type)
+    {
+    case arm_stub_cmse_branch_thumb_only:
+      return &htab->cmse_stub_sec;
+
+    default:
+      BFD_ASSERT (!arm_dedicated_stub_output_section_required (stub_type));
+      return NULL;
+    }
+
+  abort ();  /* Should be unreachable.  */
 }
 
 /* Find or create a stub section to contain a stub of type STUB_TYPE.  SECTION
@@ -4518,6 +4574,7 @@ arm_stub_required_alignment (enum elf32_arm_stub_type stub_type)
     case arm_stub_long_branch_thumb_only_pic:
     case arm_stub_long_branch_any_tls_pic:
     case arm_stub_long_branch_v4t_thumb_tls_pic:
+    case arm_stub_cmse_branch_thumb_only:
     case arm_stub_a8_veneer_blx:
       return 4;
 
@@ -4539,7 +4596,16 @@ arm_stub_sym_claimed (enum elf32_arm_stub_type stub_type)
   if (stub_type >= max_stub_type)
     abort ();  /* Should be unreachable.  */
 
-  return FALSE;
+  switch (stub_type)
+    {
+    case arm_stub_cmse_branch_thumb_only:
+      return TRUE;
+
+    default:
+      return FALSE;
+    }
+
+  abort ();  /* Should be unreachable.  */
 }
 
 /* Returns the padding needed for the dedicated section used stubs of type
@@ -4551,7 +4617,16 @@ arm_dedicated_stub_section_padding (enum elf32_arm_stub_type stub_type)
   if (stub_type >= max_stub_type)
     abort ();  /* Should be unreachable.  */
 
-  return 0;
+  switch (stub_type)
+    {
+    case arm_stub_cmse_branch_thumb_only:
+      return 32;
+
+    default:
+      return 0;
+    }
+
+  abort ();  /* Should be unreachable.  */
 }
 
 static bfd_boolean
@@ -5442,6 +5517,204 @@ elf32_arm_create_stub (struct elf32_arm_link_hash_table *htab,
   return TRUE;
 }
 
+/* Scan symbols in INPUT_BFD to identify secure entry functions needing a
+   gateway veneer to transition from non secure to secure state and create them
+   accordingly.
+
+   "ARMv8-M Security Extensions: Requirements on Development Tools" document
+   defines the conditions that govern Secure Gateway veneer creation for a
+   given symbol <SYM> as follows:
+   - it has function type
+   - it has non local binding
+   - a symbol named __acle_se_<SYM> (called special symbol) exists with the
+     same type, binding and value as <SYM> (called normal symbol).
+   An entry function can handle secure state transition itself in which case
+   its special symbol would have a different value from the normal symbol.
+
+   OUT_ATTR gives the output attributes, SYM_HASHES the symbol index to hash
+   entry mapping while HTAB gives the name to hash entry mapping.
+
+   If any secure gateway veneer is created, *STUB_CHANGED is set to TRUE.  The
+   return value gives whether a stub failed to be allocated.  */
+
+static bfd_boolean
+cmse_scan (bfd *input_bfd, struct elf32_arm_link_hash_table *htab,
+	   obj_attribute *out_attr, struct elf_link_hash_entry **sym_hashes,
+	   bfd_boolean *stub_changed)
+{
+  const struct elf_backend_data *bed;
+  Elf_Internal_Shdr *symtab_hdr;
+  unsigned i, j, sym_count, ext_start;
+  Elf_Internal_Sym *cmse_sym, *local_syms;
+  struct elf32_arm_link_hash_entry *hash, *cmse_hash = NULL;
+  enum arm_st_branch_type branch_type;
+  char *sym_name, *lsym_name;
+  bfd_vma sym_value;
+  asection *section;
+  bfd_boolean is_v8m, new_stub, created_stub, cmse_invalid, ret = TRUE;
+
+  bed = get_elf_backend_data (input_bfd);
+  symtab_hdr = &elf_tdata (input_bfd)->symtab_hdr;
+  sym_count = symtab_hdr->sh_size / bed->s->sizeof_sym;
+  ext_start = symtab_hdr->sh_info;
+  is_v8m = (out_attr[Tag_CPU_arch].i >= TAG_CPU_ARCH_V8M_BASE
+	    && out_attr[Tag_CPU_arch_profile].i == 'M');
+
+  local_syms = (Elf_Internal_Sym *) symtab_hdr->contents;
+  if (local_syms == NULL)
+    local_syms = bfd_elf_get_elf_syms (input_bfd, symtab_hdr,
+				       symtab_hdr->sh_info, 0, NULL, NULL,
+				       NULL);
+  if (symtab_hdr->sh_info && local_syms == NULL)
+    return FALSE;
+
+  /* Scan symbols.  */
+  for (i = 0; i < sym_count; i++)
+    {
+      cmse_invalid = FALSE;
+
+      if (i < ext_start)
+	{
+	  cmse_sym = &local_syms[i];
+	  /* Not a special symbol.  */
+	  if (!ARM_GET_SYM_CMSE_SPCL (cmse_sym->st_target_internal))
+	    continue;
+	  sym_name = bfd_elf_string_from_elf_section (input_bfd,
+						      symtab_hdr->sh_link,
+						      cmse_sym->st_name);
+	  /* Special symbol with local binding.  */
+	  cmse_invalid = TRUE;
+	}
+      else
+	{
+	  cmse_hash = elf32_arm_hash_entry (sym_hashes[i - ext_start]);
+	  sym_name = (char *) cmse_hash->root.root.root.string;
+
+	  /* Not a special symbol.  */
+	  if (!ARM_GET_SYM_CMSE_SPCL (cmse_hash->root.target_internal))
+	    continue;
+
+	  /* Special symbol has incorrect binding or type.  */
+	  if ((cmse_hash->root.root.type != bfd_link_hash_defined
+	       && cmse_hash->root.root.type != bfd_link_hash_defweak)
+	      || cmse_hash->root.type != STT_FUNC)
+	    cmse_invalid = TRUE;
+	}
+
+      if (!is_v8m)
+	{
+	  (*_bfd_error_handler) (_("%B: Special symbol `%s' only allowed for "
+				   "ARMv8-M architecture or later."),
+				 input_bfd, sym_name);
+	  is_v8m = TRUE; /* Avoid multiple warning.  */
+	  ret = FALSE;
+	}
+
+      if (cmse_invalid)
+	{
+	  (*_bfd_error_handler) (_("%B: invalid special symbol `%s'."),
+				 input_bfd, sym_name);
+	  (*_bfd_error_handler) (_("It must be a global or weak function "
+				   "symbol."));
+	  ret = FALSE;
+	  if (i < ext_start)
+	    continue;
+	}
+
+      sym_name += strlen (CMSE_PREFIX);
+      hash = (struct elf32_arm_link_hash_entry *)
+	elf_link_hash_lookup (&(htab)->root, sym_name, FALSE, FALSE, TRUE);
+
+      /* No associated normal symbol or it is neither global nor weak.  */
+      if (!hash
+	  || (hash->root.root.type != bfd_link_hash_defined
+	      && hash->root.root.type != bfd_link_hash_defweak)
+	  || hash->root.type != STT_FUNC)
+	{
+	  /* Initialize here to avoid warning about use of possibly
+	     uninitialized variable.  */
+	  j = 0;
+
+	  if (!hash)
+	    {
+	      /* Searching for a normal symbol with local binding.  */
+	      for (; j < ext_start; j++)
+		{
+		  lsym_name =
+		    bfd_elf_string_from_elf_section (input_bfd,
+						     symtab_hdr->sh_link,
+						     local_syms[j].st_name);
+		  if (!strcmp (sym_name, lsym_name))
+		    break;
+		}
+	    }
+
+	  if (hash || j < ext_start)
+	    {
+	      (*_bfd_error_handler)
+		(_("%B: invalid standard symbol `%s'."), input_bfd, sym_name);
+	      (*_bfd_error_handler)
+		(_("It must be a global or weak function symbol."));
+	    }
+	  else
+	    (*_bfd_error_handler)
+	      (_("%B: absent standard symbol `%s'."), input_bfd, sym_name);
+	  ret = FALSE;
+	  if (!hash)
+	    continue;
+	}
+
+      sym_value = hash->root.root.u.def.value;
+      section = hash->root.root.u.def.section;
+
+      if (cmse_hash->root.root.u.def.section != section)
+	{
+	  (*_bfd_error_handler)
+	    (_("%B: `%s' and its special symbol are in different sections."),
+	     input_bfd, sym_name);
+	  ret = FALSE;
+	}
+      if (cmse_hash->root.root.u.def.value != sym_value)
+	continue; /* Ignore: could be an entry function starting with SG.  */
+
+	/* If this section is a link-once section that will be discarded, then
+	   don't create any stubs.  */
+      if (section->output_section == NULL)
+	{
+	  (*_bfd_error_handler)
+	    (_("%B: entry function `%s' not output."), input_bfd, sym_name);
+	  continue;
+	}
+
+      if (hash->root.size == 0)
+	{
+	  (*_bfd_error_handler)
+	    (_("%B: entry function `%s' is empty."), input_bfd, sym_name);
+	  ret = FALSE;
+	}
+
+      if (!ret)
+	continue;
+      branch_type = ARM_GET_SYM_BRANCH_TYPE (hash->root.target_internal);
+      created_stub
+	= elf32_arm_create_stub (htab, arm_stub_cmse_branch_thumb_only,
+				 NULL, NULL, section, hash, sym_name,
+				 sym_value, branch_type, &new_stub);
+
+      if (!created_stub)
+	 ret = FALSE;
+      else
+	{
+	  BFD_ASSERT (new_stub);
+	  *stub_changed = TRUE;
+	}
+    }
+
+  if (!symtab_hdr->contents)
+    free (local_syms);
+  return ret;
+}
+
 /* Determine and set the size of the stub section for a final link.
 
    The basic idea here is to examine all the relocations looking for
@@ -5458,8 +5731,9 @@ elf32_arm_size_stubs (bfd *output_bfd,
 						      unsigned int),
 		      void (*layout_sections_again) (void))
 {
+  obj_attribute *out_attr;
   bfd_size_type stub_group_size;
-  bfd_boolean stubs_always_after_branch;
+  bfd_boolean m_profile, stubs_always_after_branch, first_veneer_scan = TRUE;
   struct elf32_arm_link_hash_table *htab = elf32_arm_hash_table (info);
   struct a8_erratum_fix *a8_fixes = NULL;
   unsigned int num_a8_fixes = 0, a8_fix_table_size = 10;
@@ -5488,6 +5762,8 @@ elf32_arm_size_stubs (bfd *output_bfd,
   htab->layout_sections_again = layout_sections_again;
   stubs_always_after_branch = group_size < 0;
 
+  out_attr = elf_known_obj_attributes_proc (output_bfd);
+  m_profile = out_attr[Tag_CPU_arch_profile].i == 'M';
   /* The Cortex-A8 erratum fix depends on stubs not being in the same 4K page
      as the first half of a 32-bit branch straddling two 4K pages.  This is a
      crude way of enforcing that.  */
@@ -5553,6 +5829,18 @@ elf32_arm_size_stubs (bfd *output_bfd,
 	  if (symtab_hdr->sh_info == 0)
 	    continue;
 
+	  /* Limit scan of symbols to object file whose profile is
+	     Microcontroller to not hinder performance in the general case.  */
+	  if (m_profile && first_veneer_scan)
+	    {
+	      struct elf_link_hash_entry **sym_hashes;
+
+	      sym_hashes = elf_sym_hashes (input_bfd);
+	      if (!cmse_scan (input_bfd, htab, out_attr, sym_hashes,
+			      &stub_changed))
+		goto error_ret_free_local;
+	    }
+
 	  /* Walk over each section attached to the input bfd.  */
 	  for (section = input_bfd->sections;
 	       section != NULL;
@@ -5939,6 +6227,7 @@ elf32_arm_size_stubs (bfd *output_bfd,
 
       /* Ask the linker to do its stuff.  */
       (*htab->layout_sections_again) ();
+      first_veneer_scan = FALSE;
     }
 
   /* Add stubs for Cortex-A8 erratum fixes now.  */
@@ -9280,7 +9569,8 @@ elf32_arm_final_link_relocate (reloc_howto_type *           howto,
   /* Find out whether the symbol has a PLT.  Set ST_VALUE, BRANCH_TYPE and
      VALUE appropriately for relocations that we resolve at link time.  */
   has_iplt_entry = FALSE;
-  if (elf32_arm_get_plt_info (input_bfd, eh, r_symndx, &root_plt, &arm_plt)
+  if (elf32_arm_get_plt_info (input_bfd, globals, eh, r_symndx, &root_plt,
+			      &arm_plt)
       && root_plt->offset != (bfd_vma) -1)
     {
       plt_offset = root_plt->offset;
@@ -13693,7 +13983,8 @@ elf32_arm_gc_sweep_hook (bfd *                     abfd,
 	}
 
       if (may_need_local_target_p
-	  && elf32_arm_get_plt_info (abfd, eh, r_symndx, &root_plt, &arm_plt))
+	  && elf32_arm_get_plt_info (abfd, globals, eh, r_symndx, &root_plt,
+				     &arm_plt))
 	{
 	  /* If PLT refcount book-keeping is wrong and too low, we'll
 	     see a zero value (going to -1) for the root PLT reference
@@ -14161,7 +14452,11 @@ elf32_arm_check_relocs (bfd *abfd, struct bfd_link_info *info,
 }
 
 /* Unwinding tables are not referenced directly.  This pass marks them as
-   required if the corresponding code section is marked.  */
+   required if the corresponding code section is marked.  Similarly, ARMv8-M
+   secure entry functions can only be referenced by SG veneers which are
+   created after the GC process. They need to be marked in case they reside in
+   their own section (as would be the case if code was compiled with
+   -ffunction-sections).  */
 
 static bfd_boolean
 elf32_arm_gc_mark_extra_sections (struct bfd_link_info *info,
@@ -14169,10 +14464,21 @@ elf32_arm_gc_mark_extra_sections (struct bfd_link_info *info,
 {
   bfd *sub;
   Elf_Internal_Shdr **elf_shdrp;
-  bfd_boolean again;
+  asection *cmse_sec;
+  obj_attribute *out_attr;
+  Elf_Internal_Shdr *symtab_hdr;
+  unsigned i, sym_count, ext_start;
+  const struct elf_backend_data *bed;
+  struct elf_link_hash_entry **sym_hashes;
+  struct elf32_arm_link_hash_entry *cmse_hash;
+  bfd_boolean again, is_v8m, first_bfd_browse = TRUE;
 
   _bfd_elf_gc_mark_extra_sections (info, gc_mark_hook);
 
+  out_attr = elf_known_obj_attributes_proc (info->output_bfd);
+  is_v8m = out_attr[Tag_CPU_arch].i >= TAG_CPU_ARCH_V8M_BASE
+	   && out_attr[Tag_CPU_arch_profile].i == 'M';
+
   /* Marking EH data may cause additional code sections to be marked,
      requiring multiple passes.  */
   again = TRUE;
@@ -14203,7 +14509,34 @@ elf32_arm_gc_mark_extra_sections (struct bfd_link_info *info,
 		    return FALSE;
 		}
 	    }
+
+	  /* Mark section holding ARMv8-M secure entry functions.  We mark all
+	     of them so no need for a second browsing.  */
+	  if (is_v8m && first_bfd_browse)
+	    {
+	      sym_hashes = elf_sym_hashes (sub);
+	      bed = get_elf_backend_data (sub);
+	      symtab_hdr = &elf_tdata (sub)->symtab_hdr;
+	      sym_count = symtab_hdr->sh_size / bed->s->sizeof_sym;
+	      ext_start = symtab_hdr->sh_info;
+
+	      /* Scan symbols.  */
+	      for (i = ext_start; i < sym_count; i++)
+		{
+		  cmse_hash = elf32_arm_hash_entry (sym_hashes[i - ext_start]);
+
+		  /* Assume it is a special symbol.  If not, cmse_scan will
+		     warn about it and user can do something about it.  */
+		  if (ARM_GET_SYM_CMSE_SPCL (cmse_hash->root.target_internal))
+		    {
+		      cmse_sec = cmse_hash->root.root.u.def.section;
+		      if (!_bfd_elf_gc_mark (info, cmse_sec, gc_mark_hook))
+			return FALSE;
+		    }
+		}
+	    }
 	}
+      first_bfd_browse = FALSE;
     }
 
   return TRUE;
@@ -17855,6 +18188,9 @@ elf32_arm_swap_symbol_in (bfd * abfd,
 			  const void *pshn,
 			  Elf_Internal_Sym *dst)
 {
+  Elf_Internal_Shdr *symtab_hdr;
+  const char *name = NULL;
+
   if (!bfd_elf32_swap_symbol_in (abfd, psrc, pshn, dst))
     return FALSE;
   dst->st_target_internal = 0;
@@ -17883,6 +18219,13 @@ elf32_arm_swap_symbol_in (bfd * abfd,
   else
     ARM_SET_SYM_BRANCH_TYPE (dst->st_target_internal, ST_BRANCH_UNKNOWN);
 
+  /* Mark CMSE special symbols.  */
+  symtab_hdr = & elf_symtab_hdr (abfd);
+  if (symtab_hdr->sh_size)
+    name = bfd_elf_sym_name (abfd, symtab_hdr, dst, NULL);
+  if (name && CONST_STRNEQ (name, CMSE_PREFIX))
+    ARM_SET_SYM_CMSE_SPCL (dst->st_target_internal);
+
   return TRUE;
 }
 
diff --git a/include/ChangeLog b/include/ChangeLog
index f48ed0a4188..4d51d0b367b 100644
--- a/include/ChangeLog
+++ b/include/ChangeLog
@@ -1,3 +1,8 @@
+2016-08-04  Thomas Preud'homme  <thomas.preudhomme@arm.com>
+
+	* arm.h (ARM_GET_SYM_CMSE_SPCL): Define macro.
+	(ARM_SET_SYM_CMSE_SPCL): Likewise.
+
 2016-08-01  Andrew Jenner  <andrew@codesourcery.com>
 
 	* opcode/ppc.h (PPC_OPCODE_E200Z4): New define.
diff --git a/include/elf/arm.h b/include/elf/arm.h
index 27ce6b88ce5..87a6e5869d6 100644
--- a/include/elf/arm.h
+++ b/include/elf/arm.h
@@ -384,4 +384,11 @@ enum arm_st_branch_type {
 	   | ((TYPE) & ENUM_ARM_ST_BRANCH_TYPE_BITMASK))
 #endif
 
+/* Get or set whether a symbol is a special symbol of an entry function of CMSE
+   secure code.  */
+#define ARM_GET_SYM_CMSE_SPCL(SYM_TARGET_INTERNAL) \
+  (((SYM_TARGET_INTERNAL) >> 2) & 1)
+#define ARM_SET_SYM_CMSE_SPCL(SYM_TARGET_INTERNAL) \
+  (SYM_TARGET_INTERNAL) |= 4
+
 #endif /* _ELF_ARM_H */
diff --git a/ld/ChangeLog b/ld/ChangeLog
index 8dec408ff08..49f79726f2b 100644
--- a/ld/ChangeLog
+++ b/ld/ChangeLog
@@ -1,3 +1,18 @@
+2016-08-04  Thomas Preud'homme  <thomas.preudhomme@arm.com>
+
+	* ld.texinfo (Placement of SG veneers): New concept entry.
+	* testsuite/ld-arm/arm-elf.exp
+	(Secure gateway veneers: no .gnu.sgstubs section): New test.
+	(Secure gateway veneers: wrong entry functions): Likewise.
+	(Secure gateway veneers (ARMv8-M Baseline)): Likewise.
+	(Secure gateway veneers (ARMv8-M Mainline)): Likewise.
+	* testsuite/ld-arm/cmse-veneers.s: New file.
+	* testsuite/ld-arm/cmse-veneers.d: Likewise.
+	* testsuite/ld-arm/cmse-veneers.rd: Likewise.
+	* testsuite/ld-arm/cmse-veneers.sd: Likewise.
+	* testsuite/ld-arm/cmse-veneers-no-gnu_sgstubs.out: Likewise.
+	* testsuite/ld-arm/cmse-veneers-wrong-entryfct.out: Likewise.
+
 2016-08-02  Nick Clifton  <nickc@redhat.com>
 
 	PR ld/17739
diff --git a/ld/ld.texinfo b/ld/ld.texinfo
index b2dff10e449..af8cee39561 100644
--- a/ld/ld.texinfo
+++ b/ld/ld.texinfo
@@ -6853,6 +6853,12 @@ entries which only support 512Mb of code.
 The @samp{--no-apply-dynamic-relocs} option makes AArch64 linker do not apply
 link-time values for dynamic relocations.
 
+@cindex Placement of SG veneers
+All SG veneers are placed in the special output section @code{.gnu.sgstubs}.
+Its start address must be set, either with the command line option
+@samp{--section-start} or in a linker script, to indicate where to place these
+veneers in memory.
+
 @ifclear GENERIC
 @lowersections
 @end ifclear
diff --git a/ld/testsuite/ld-arm/arm-elf.exp b/ld/testsuite/ld-arm/arm-elf.exp
index d0c9a2f240d..b3c8a84b86f 100644
--- a/ld/testsuite/ld-arm/arm-elf.exp
+++ b/ld/testsuite/ld-arm/arm-elf.exp
@@ -642,6 +642,33 @@ set armeabitests_nonacl {
      {{objdump -d jump-reloc-veneers-long.d}}
      "jump-reloc-veneers-long"}
 
+    {"Secure gateway veneers: no .gnu.sgstubs section" "" ""
+     "-march=armv8-m.base -mthumb"
+     {cmse-veneers.s}
+     {{ld cmse-veneers-no-gnu_sgstubs.out}}
+     "cmse-veneers-no-gnu_sgstubs"}
+    {"Secure gateway veneers: wrong entry functions" "" ""
+     "-march=armv7-m -mthumb --defsym CHECK_ERRORS=1"
+     {cmse-veneers.s}
+     {{ld cmse-veneers-wrong-entryfct.out}}
+     "cmse-veneers-wrong-entryfct"}
+    {"Secure gateway veneers (ARMv8-M Baseline)"
+     "-Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 --gc-sections" ""
+     "-march=armv8-m.base -mthumb"
+     {cmse-veneers.s}
+     {{objdump {-d -j .gnu.sgstubs} cmse-veneers.d}
+      {objdump {-h -j .gnu.sgstubs} cmse-veneers.sd}
+      {nm {} cmse-veneers.rd}}
+     "cmse-veneers-baseline"}
+    {"Secure gateway veneers (ARMv8-M Mainline)"
+     "-Ttext=0x8000 --section-start .gnu.sgstubs=0x20000 --gc-sections" ""
+     "-march=armv8-m.main -mthumb"
+     {cmse-veneers.s}
+     {{objdump {-d -j .gnu.sgstubs} cmse-veneers.d}
+      {objdump {-h -j .gnu.sgstubs} cmse-veneers.sd}
+      {nm {} cmse-veneers.rd}}
+     "cmse-veneers-mainline"}
+
     {"R_ARM_THM_JUMP19 Relocation veneers: Short"
      "--section-start destsect=0x000108002 --section-start .text=0x8000" ""
      "-march=armv7-m -mthumb"
diff --git a/ld/testsuite/ld-arm/cmse-veneers-no-gnu_sgstubs.out b/ld/testsuite/ld-arm/cmse-veneers-no-gnu_sgstubs.out
new file mode 100644
index 00000000000..9d1e5ba3215
--- /dev/null
+++ b/ld/testsuite/ld-arm/cmse-veneers-no-gnu_sgstubs.out
@@ -0,0 +1,3 @@
+.*: No address assigned to the veneers output section .gnu.sgstubs
+.*: cannot size stub section: Invalid operation
+#...
diff --git a/ld/testsuite/ld-arm/cmse-veneers-wrong-entryfct.out b/ld/testsuite/ld-arm/cmse-veneers-wrong-entryfct.out
new file mode 100644
index 00000000000..fd4766ab877
--- /dev/null
+++ b/ld/testsuite/ld-arm/cmse-veneers-wrong-entryfct.out
@@ -0,0 +1,19 @@
+.*: .*: Special symbol `__acle_se_loc_entry_veneer1' only allowed for ARMv8-M architecture or later.
+.*: .*: invalid .* symbol `.*loc_entry_veneer1'.
+.*: It must be a global or weak function symbol.
+.*: .*: invalid special symbol `__acle_se_loc_entry_veneer2'.
+.*: It must be a global or weak function symbol.
+.*: .*: invalid special symbol `__acle_se_loc_entry_veneer4'.
+.*: It must be a global or weak function symbol.
+.*: .*: invalid standard symbol `loc_entry_veneer3'.
+.*: It must be a global or weak function symbol.
+.*: .*: invalid standard symbol `loc_entry_veneer5'.
+.*: It must be a global or weak function symbol.
+.*: .*: absent standard symbol `fake_entry_veneer1'.
+.*: .*: invalid standard symbol `obj_entry_veneer1'.
+.*: It must be a global or weak function symbol.
+.*: .*: invalid special symbol `__acle_se_obj_entry_veneer2'.
+.*: It must be a global or weak function symbol.
+.*: .*: `fake_entry_veneer2' and its special symbol are in different sections.
+.*: cannot size stub section: Invalid operation
+#...
diff --git a/ld/testsuite/ld-arm/cmse-veneers.d b/ld/testsuite/ld-arm/cmse-veneers.d
new file mode 100644
index 00000000000..6a44a2b5dce
--- /dev/null
+++ b/ld/testsuite/ld-arm/cmse-veneers.d
@@ -0,0 +1,21 @@
+
+.*
+
+
+Disassembly of section \.gnu.sgstubs:
+
+00020000 <glob_entry_veneer2>:
+   20000:	e97f e97f 	sg
+   20004:	f7e8 b800 	b\.w	8008 <__acle_se_glob_entry_veneer2>
+
+00020008 <weak_entry_veneer2>:
+   20008:	e97f e97f 	sg
+   2000c:	f7e7 bffe 	b\.w	800c <__acle_se_weak_entry_veneer2>
+
+00020010 <glob_entry_veneer1>:
+   20010:	e97f e97f 	sg
+   20014:	f7e7 bff4 	b\.w	8000 <__acle_se_glob_entry_veneer1>
+
+00020018 <weak_entry_veneer1>:
+   20018:	e97f e97f 	sg
+   2001c:	f7e7 bff2 	b\.w	8004 <__acle_se_weak_entry_veneer1>
diff --git a/ld/testsuite/ld-arm/cmse-veneers.rd b/ld/testsuite/ld-arm/cmse-veneers.rd
new file mode 100644
index 00000000000..20fad961bd8
--- /dev/null
+++ b/ld/testsuite/ld-arm/cmse-veneers.rd
@@ -0,0 +1,9 @@
+#...
+[0-9a-f]+ T glob_entry_fct
+#...
+[0-9a-f]+ T glob_entry_veneer1
+[0-9a-f]+ T glob_entry_veneer2
+#...
+[0-9a-f]+ W weak_entry_veneer1
+[0-9a-f]+ W weak_entry_veneer2
+#...
diff --git a/ld/testsuite/ld-arm/cmse-veneers.s b/ld/testsuite/ld-arm/cmse-veneers.s
new file mode 100644
index 00000000000..d5c57f646a7
--- /dev/null
+++ b/ld/testsuite/ld-arm/cmse-veneers.s
@@ -0,0 +1,97 @@
+	.syntax unified
+	.thumb
+	.file	"foo.c"
+	.text
+
+.macro	decltype	name, type
+.ifc \type,object
+	.data
+.else
+	.thumb
+	.thumb_func
+.endif
+	.type	\name, %\type
+.endm
+
+
+.macro	entry	name, type, vis, typespc, visspc, entry_fct
+	.align	2
+.ifb \visspc
+	.\vis	__acle_se_\name
+.else
+	.\visspc	__acle_se_\name
+.endif
+	.\vis	\name
+	.thumb
+	.thumb_func
+.ifb \typespc
+	decltype	__acle_se_\name, \type
+.else
+	decltype	__acle_se_\name, \typespc
+.endif
+	decltype	\name, \type
+__acle_se_\name:
+	\entry_fct
+\name:
+.ifc \type,object
+	.word 42
+.else
+	nop
+.endif
+	.size	\name, .-\name
+	.size	__acle_se_\name, .-__acle_se_\name
+.endm
+
+
+.ifndef CHECK_ERRORS
+	@ Valid setups for veneer generation
+	entry glob_entry_veneer1, function, global
+	entry weak_entry_veneer1, function, weak
+	entry glob_entry_veneer2, function, global, visspc=weak
+	entry weak_entry_veneer2, function, weak, visspc=global
+
+	@ Valid setup for entry function without SG veneer
+	entry glob_entry_fct, function, global, entry_fct=nop
+
+.else
+	@ Invalid setups for veneer generation (visibility)
+	entry loc_entry_veneer1, function, local
+	entry loc_entry_veneer2, function, global, visspc=local
+	entry loc_entry_veneer3, function, local, visspc=global
+	entry loc_entry_veneer4, function, weak, visspc=local
+	entry loc_entry_veneer5, function, local, visspc=weak
+
+	@ Invalid setups for veneer generation (absent standard symbol)
+	.align	2
+	.global	__acle_se_fake_entry_veneer1
+	.thumb
+	.thumb_func
+	.type	__acle_se_fake_entry_veneer1, %function
+__acle_se_fake_entry_veneer1:
+	nop
+	.size	__acle_se_fake_entry_veneer1, .-__acle_se_fake_entry_veneer1
+
+	@ Invalid setups for veneer generation (type)
+	entry obj_entry_veneer1, object, global, typespc=function
+	entry obj_entry_veneer2, function, global, typespc=object
+
+	@ Invalid setup for veneer generation (sections)
+	.section .text.sub1
+	.align	2
+	.thumb
+	.thumb_func
+	.global	__acle_se_fake_entry_veneer2
+	.type	__acle_se_fake_entry_veneer2, %function
+__acle_se_fake_entry_veneer2:
+	nop
+	.size	__acle_se_fake_entry_veneer2, .-__acle_se_fake_entry_veneer2
+	.section .text.sub2
+	.align	2
+	.thumb
+	.thumb_func
+	.global	fake_entry_veneer2
+	.type	fake_entry_veneer2, %function
+fake_entry_veneer2:
+	nop
+	.size	fake_entry_veneer2, .-fake_entry_veneer2
+.endif
diff --git a/ld/testsuite/ld-arm/cmse-veneers.sd b/ld/testsuite/ld-arm/cmse-veneers.sd
new file mode 100644
index 00000000000..99bfc8f37c2
--- /dev/null
+++ b/ld/testsuite/ld-arm/cmse-veneers.sd
@@ -0,0 +1,7 @@
+
+.*
+
+Sections:
+Idx Name          Size      VMA       LMA       File off  Algn
+  \d+ \.gnu\.sgstubs  00000020  00020000  00020000  00010000  2\*\*5
+                  CONTENTS, ALLOC, LOAD, READONLY, CODE