Re: [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>]

On Tuesday 29 March 2016 15:39:25 Thomas Preudhomme wrote:
> Hi,
> 
> This patch is part of a patch series to add support for ARMv8-M Security
> Extensions[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]

Please find an updated version without the switch case for the 
arm_dedicated_stub_* functions.

ChangeLog entries are unchanged:

*** 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 
02977358ac69deab379f2d826c44bfc5efa49e1a..ab878b20905c907b3496317c7ed1c9c698d850c9 
100644
--- a/bfd/elf32-arm.c
+++ b/bfd/elf32-arm.c
@@ -4136,68 +4136,155 @@ 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.  */
+
+  return FALSE;
+}
+
+/* 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.  */
+
+  BFD_ASSERT (!arm_dedicated_stub_output_section_required (stub_type));
+  return 0;
+}
+
+/* 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.  */
+
+  BFD_ASSERT (!arm_dedicated_stub_output_section_required (stub_type));
+  return NULL;
+}
+
+/* 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.  */
+
+  BFD_ASSERT (!arm_dedicated_stub_output_section_required (stub_type));
+  return NULL;
+}
+
+/* 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;
-
-  link_sec = htab->stub_group[section->id].link_sec;
-  BFD_ASSERT (link_sec != NULL);
-  stub_sec = htab->stub_group[section->id].stub_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;
 
-  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;
 
@@ -5187,7 +5274,7 @@ 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)
@@ -5685,7 +5772,7 @@ 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;
@@ -6479,6 +6566,37 @@ 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)

Best regards,

Thomas