[PATCH, binutils, ARM 6/11] Support for dedicated output section for some veneer types

[Thomas Preudhomme <thomas dot preudhomme at foss dot arm dot com>]

Hi,

This patch is part of a patch series to add support for ARMv8-M security 
extension[1] to GNU ld. This specific patch adds support for having veneers of 
a given type in a dedicated output section.

ARM v8-M security extensions require [3] secure gateway veneers to be 
generated for (secure) entry function in order for code to transition from 
non-secure state to secure state when calling these entry function. One 
requirement for these veneers [4] is to be able to keep their addresses when 
the secure code is relinked in order to avoid relinking the non secure code 
with the secure code. This patch adds support for generating these veneers in 
a dedicated output section and expect the user to specify the address of that 
section (either via --section-start parameter or in the linker script). This 
ensure that they are placed in a memory area with sufficient space for more 
veneers to be added. Ensuring that existing veneers keep their addresses when 
the secure executable is relinked is handled by a subsequent patch of this 
patch series.


[1] Software requirements for ARMv8-M security extension are described in 
document ARM-ECM-0359818 [2]
[2] Available on http://infocenter.arm.com in Developer guides and articles > 
Software development > ARMÂv8-M Security Extensions: Requirements on 
Development Tools
[3] See section 3.4.3 and requirement 44 of ARM-ECM-0359818 [2]
[4] requirement 14 and following comment of ARM-ECM-0359818 [2]


ChangeLog entries are as follow:

*** bfd/ChangeLog ***

2016-02-17  Thomas Preud'homme  <thomas.preudhomme@arm.com>

        * bfd-in.h (bfd_elf32_arm_keep_private_stub_output_sections): Declare
        bfd hook.
        * bfd-in2.h: Regenerate.
        * elf32-arm.c (arm_dedicated_stub_output_section_required): New
        function.
        (arm_dedicated_stub_output_section_required_alignment): Likewise.
        (arm_dedicated_stub_output_section_name): Likewise.
        (arm_dedicated_stub_input_section_ptr): Likewise.
        (elf32_arm_create_or_find_stub_sec): Add stub type parameter and
        function description comment. Add support for dedicated output stub
        section to given stub types.
        (elf32_arm_add_stub): Add a stub type parameter and pass it down to
        elf32_arm_create_or_find_stub_sec.
        (elf32_arm_create_stub): Pass stub type down to elf32_arm_add_stub.
        (elf32_arm_size_stubs): Pass stub type when calling
        elf32_arm_create_or_find_stub_sec for Cortex-A8 erratum veneers.
        (bfd_elf32_arm_keep_private_stub_output_sections): New function.

*** ld/ChangeLog ***

2016-01-04  Thomas Preud'homme  <thomas.preudhomme@arm.com>

        * emultempl/armelf.em (arm_elf_before_allocation): Call
        bfd_elf32_arm_keep_private_stub_output_sections before generic
        before_allocation function.


diff --git a/bfd/bfd-in.h b/bfd/bfd-in.h
index 
571a63672bfda3b4310adf791fb28cf23ae09ae0..c66ce3bba1ad1d1ce670f7404e465834cbf43fb1 
100644
--- a/bfd/bfd-in.h
+++ b/bfd/bfd-in.h
@@ -903,6 +903,9 @@ extern bfd_boolean bfd_elf32_arm_get_bfd_for_interworking
 extern bfd_boolean bfd_elf32_arm_add_glue_sections_to_bfd
   (bfd *, struct bfd_link_info *);
 
+extern void bfd_elf32_arm_keep_private_stub_output_sections
+  (struct bfd_link_info *);
+
 /* ELF ARM mapping symbol support.  */
 #define BFD_ARM_SPECIAL_SYM_TYPE_MAP	(1 << 0)
 #define BFD_ARM_SPECIAL_SYM_TYPE_TAG	(1 << 1)
diff --git a/bfd/bfd-in2.h b/bfd/bfd-in2.h
index 
294da5e1c163bd443c73a99778880a986a08566b..afaca4ef19e49cf9899952a84a90c60fcd3fc8dd 
100644
--- a/bfd/bfd-in2.h
+++ b/bfd/bfd-in2.h
@@ -910,6 +910,9 @@ extern bfd_boolean bfd_elf32_arm_get_bfd_for_interworking
 extern bfd_boolean bfd_elf32_arm_add_glue_sections_to_bfd
   (bfd *, struct bfd_link_info *);
 
+extern void bfd_elf32_arm_keep_private_stub_output_sections
+  (struct bfd_link_info *);
+
 /* ELF ARM mapping symbol support.  */
 #define BFD_ARM_SPECIAL_SYM_TYPE_MAP	(1 << 0)
 #define BFD_ARM_SPECIAL_SYM_TYPE_TAG	(1 << 1)
diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
index 
7beac0a3b81239a1b87db41518232e74b2531c46..af5f1f2417576dc496bf242f381f9e3464350d9a 
100644
--- a/bfd/elf32-arm.c
+++ b/bfd/elf32-arm.c
@@ -4135,68 +4135,179 @@ elf32_arm_get_stub_entry (const asection 
*input_section,
   return stub_entry;
 }
 
-/* Find or create a stub section.  Returns a pointer to the stub section, and
-   the section to which the stub section will be attached (in *LINK_SEC_P).
+/* Whether veneers of type STUB_TYPE require to be in a dedicated output
+   section.  */
+
+static bfd_boolean
+arm_dedicated_stub_output_section_required (enum elf32_arm_stub_type 
stub_type)
+{
+  if (stub_type >= max_stub_type)
+    abort ();  /* Should be unreachable.  */
+
+  switch (stub_type)
+    {
+    default:
+      return FALSE;
+    }
+
+  abort ();  /* Should be unreachable.  */
+}
+
+/* Required alignment (as a power of 2) for the dedicated section holding
+   veneers of type STUB_TYPE, or 0 if veneers of this type are interspersed
+   with input sections.  */
+
+static int
+arm_dedicated_stub_output_section_required_alignment
+  (enum elf32_arm_stub_type stub_type)
+{
+  if (stub_type >= max_stub_type)
+    abort ();  /* Should be unreachable.  */
+
+  switch (stub_type)
+    {
+    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
+   NULL if veneers of this type are interspersed with input sections.  */
+
+static const char *
+arm_dedicated_stub_output_section_name (enum elf32_arm_stub_type stub_type)
+{
+  if (stub_type >= max_stub_type)
+    abort ();  /* Should be unreachable.  */
+
+  switch (stub_type)
+    {
+    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,
+   returns the address of the hash table field in HTAB holding a pointer to 
the
+   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)
+{
+  if (stub_type >= max_stub_type)
+    abort ();  /* Should be unreachable.  */
+
+  switch (stub_type)
+    {
+    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
+   is the section that branch into veneer and can be NULL if stub should go 
in
+   a dedicated output section.  Returns a pointer to the stub section, and 
the
+   section to which the stub section will be attached (in *LINK_SEC_P).
    LINK_SEC_P may be NULL.  */
 
 static asection *
 elf32_arm_create_or_find_stub_sec (asection **link_sec_p, asection *section,
-				   struct elf32_arm_link_hash_table *htab)
+				   struct elf32_arm_link_hash_table *htab,
+				   enum elf32_arm_stub_type stub_type)
 {
-  asection *link_sec;
-  asection *stub_sec;
-  asection *out_sec;
+  asection *link_sec, *out_sec, **stub_sec_p;
+  const char *stub_sec_prefix;
+  bfd_boolean dedicated_output_section =
+    arm_dedicated_stub_output_section_required (stub_type);
+  int align;
 
-  link_sec = htab->stub_group[section->id].link_sec;
-  BFD_ASSERT (link_sec != NULL);
-  stub_sec = htab->stub_group[section->id].stub_sec;
-
-  if (stub_sec == NULL)
+  if (dedicated_output_section)
     {
-      stub_sec = htab->stub_group[link_sec->id].stub_sec;
-      if (stub_sec == NULL)
+      bfd *output_bfd = htab->obfd;
+      const char *out_sec_name =
+	arm_dedicated_stub_output_section_name (stub_type);
+      link_sec = NULL;
+      stub_sec_p = arm_dedicated_stub_input_section_ptr (htab, stub_type);
+      stub_sec_prefix = out_sec_name;
+      align = arm_dedicated_stub_output_section_required_alignment 
(stub_type);
+      out_sec = bfd_get_section_by_name (output_bfd, out_sec_name);
+      if (out_sec == NULL)
 	{
-	  size_t namelen;
-	  bfd_size_type len;
-	  char *s_name;
-
-	  namelen = strlen (link_sec->name);
-	  len = namelen + sizeof (STUB_SUFFIX);
-	  s_name = (char *) bfd_alloc (htab->stub_bfd, len);
-	  if (s_name == NULL)
-	    return NULL;
-
-	  memcpy (s_name, link_sec->name, namelen);
-	  memcpy (s_name + namelen, STUB_SUFFIX, sizeof (STUB_SUFFIX));
-	  out_sec = link_sec->output_section;
-	  stub_sec = (*htab->add_stub_section) (s_name, out_sec, link_sec,
-						htab->nacl_p ? 4 : 3);
-	  if (stub_sec == NULL)
-	    return NULL;
-	  htab->stub_group[link_sec->id].stub_sec = stub_sec;
+	  (*_bfd_error_handler) (_("No address assigned to the veneers output "
+				   "section %s"), out_sec_name);
+	  return NULL;
 	}
-      htab->stub_group[section->id].stub_sec = stub_sec;
     }
+  else
+    {
+      link_sec = htab->stub_group[section->id].link_sec;
+      BFD_ASSERT (link_sec != NULL);
+      stub_sec_p = &htab->stub_group[section->id].stub_sec;
+      if (*stub_sec_p == NULL)
+	stub_sec_p = &htab->stub_group[link_sec->id].stub_sec;
+      stub_sec_prefix = link_sec->name;
+      out_sec = link_sec->output_section;
+      align = htab->nacl_p ? 4 : 3;
+    }
+
+  if (*stub_sec_p == NULL)
+    {
+      size_t namelen;
+      bfd_size_type len;
+      char *s_name;
+
+      namelen = strlen (stub_sec_prefix);
+      len = namelen + sizeof (STUB_SUFFIX);
+      s_name = (char *) bfd_alloc (htab->stub_bfd, len);
+      if (s_name == NULL)
+	return NULL;
+
+      memcpy (s_name, stub_sec_prefix, namelen);
+      memcpy (s_name + namelen, STUB_SUFFIX, sizeof (STUB_SUFFIX));
+      *stub_sec_p = (*htab->add_stub_section) (s_name, out_sec, link_sec,
+					       align);
+      if (*stub_sec_p == NULL)
+	return NULL;
+
+      out_sec->flags |= SEC_ALLOC | SEC_LOAD | SEC_READONLY | SEC_CODE
+			| SEC_HAS_CONTENTS | SEC_RELOC | SEC_IN_MEMORY
+			| SEC_KEEP;
+    }
+
+  if (!dedicated_output_section)
+    htab->stub_group[section->id].stub_sec = *stub_sec_p;
 
   if (link_sec_p)
     *link_sec_p = link_sec;
 
-  return stub_sec;
+  return *stub_sec_p;
 }
 
 /* Add a new stub entry to the stub hash.  Not all fields of the new
    stub entry are initialised.  */
 
 static struct elf32_arm_stub_hash_entry *
-elf32_arm_add_stub (const char *stub_name,
-		    asection *section,
-		    struct elf32_arm_link_hash_table *htab)
+elf32_arm_add_stub (const char *stub_name, asection *section,
+		    struct elf32_arm_link_hash_table *htab,
+		    enum elf32_arm_stub_type stub_type)
 {
   asection *link_sec;
   asection *stub_sec;
   struct elf32_arm_stub_hash_entry *stub_entry;
 
-  stub_sec = elf32_arm_create_or_find_stub_sec (&link_sec, section, htab);
+  stub_sec = elf32_arm_create_or_find_stub_sec (&link_sec, section, htab,
+						stub_type);
   if (stub_sec == NULL)
     return NULL;
 
@@ -5192,7 +5303,7 @@ elf32_arm_create_stub (struct elf32_arm_link_hash_table 
*htab,
       return TRUE;
     }
 
-  stub_entry = elf32_arm_add_stub (stub_name, section, htab);
+  stub_entry = elf32_arm_add_stub (stub_name, section, htab, stub_type);
   if (stub_entry == NULL)
     {
       if (!sym_claimed)
@@ -5691,7 +5802,7 @@ elf32_arm_size_stubs (bfd *output_bfd,
 	for (i = 0; i < num_a8_fixes; i++)
 	  {
 	    stub_sec = elf32_arm_create_or_find_stub_sec (NULL,
-			 a8_fixes[i].section, htab);
+			 a8_fixes[i].section, htab, a8_fixes[i].stub_type);
 
 	    if (stub_sec == NULL)
 	      goto error_ret_free_local;
@@ -6485,6 +6596,37 @@ bfd_elf32_arm_add_glue_sections_to_bfd (bfd *abfd,
     && arm_make_glue_section (abfd, STM32L4XX_ERRATUM_VENEER_SECTION_NAME);
 }
 
+/* Mark output sections of veneers needing a dedicated one with SEC_KEEP.  
This
+   ensures they are not marked for deletion by
+   strip_excluded_output_sections () when veneers are going to be created
+   later.  Not doing so would trigger assert on empty section size in
+   lang_size_sections_1 ().  */
+
+void
+bfd_elf32_arm_keep_private_stub_output_sections (struct bfd_link_info *info)
+{
+  enum elf32_arm_stub_type stub_type;
+
+  /* If we are only performing a partial
+     link do not bother adding the glue.  */
+  if (bfd_link_relocatable (info))
+    return;
+
+  for (stub_type = arm_stub_none + 1; stub_type < max_stub_type; stub_type++)
+    {
+      asection *out_sec;
+      const char *out_sec_name;
+
+      if (!arm_dedicated_stub_output_section_required (stub_type))
+	continue;
+
+     out_sec_name = arm_dedicated_stub_output_section_name (stub_type);
+     out_sec = bfd_get_section_by_name (info->output_bfd, out_sec_name);
+     if (out_sec != NULL)
+	out_sec->flags |= SEC_KEEP;
+    }
+}
+
 /* Select a BFD to be used to hold the sections used by the glue code.
    This function is called from the linker scripts in ld/emultempl/
    {armelf/pe}.em.  */
diff --git a/ld/emultempl/armelf.em b/ld/emultempl/armelf.em
index 
caa2fbfff3633f2a7f69a7b197574eed8279d6c4..6074824f72d6f607449000702e7c5945bfe412ef 
100644
--- a/ld/emultempl/armelf.em
+++ b/ld/emultempl/armelf.em
@@ -83,6 +83,10 @@ arm_elf_before_allocation (void)
   /* Auto-select Cortex-A8 erratum fix if it wasn't explicitly specified.  */
   bfd_elf32_arm_set_cortex_a8_fix (link_info.output_bfd, &link_info);
 
+  /* Ensure the output sections of veneers needing a dedicated one is not
+     removed.  */
+  bfd_elf32_arm_keep_private_stub_output_sections (&link_info);
+
   /* We should be able to set the size of the interworking stub section.  We
      can't do it until later if we have dynamic sections, though.  */
   if (elf_hash_table (&link_info)->dynobj == NULL)



The patch doesn't show any regression when running the binutils-gdb testsuite 
for the arm-none-eabi target.

Best regards,

Thomas