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[RFC PATCH, binutils, ARM 2/11, ping] Factor our stub creation in ARM backend

Thomas Preudhomme thomas.preudhomme@foss.arm.com
Mon Apr 4 14:01:00 GMT 2016 
On Wednesday 30 March 2016 11:11:01 Christophe Lyon wrote:
> On 29 March 2016 at 16:33, Thomas Preudhomme
> 
> <thomas.preudhomme@foss.arm.com> wrote:
> > Ping?
> > 
> > On Wednesday 23 December 2015 15:55:26 Thomas Preud'homme wrote:
> >> Hi,
> >> 
> >> [Posting patch series as RFC]
> >> 
> >> This patch is part of a patch series to add support for ARMv8-M security
> >> extension[1] to GNU ld. This specific patch factors out the code to
> >> create
> >> a stub in ARM backend to avoid code duplication in subsequent patches
> >> adding new code for creating Secure Gateway veneers.
> >> 
> >> 
> >> [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 > ARM®v8-M Security
> >> Extensions: Requirements on Development Tools
> >> 
> >> ChangeLog entries is as follows:
> >> 
> >> 
> >> *** bfd/ChangeLog ***
> >> 
> >> 2015-12-16  Thomas Preud'homme  <thomas.preudhomme@arm.com>
> >> 
> >>         * elf32-arm.c (elf32_arm_create_stub): New function.
> >>         (elf32_arm_size_stubs): Use elf32_arm_create_stub for stub
> >>         creation.
> >> 
> >> diff --git a/bfd/elf32-arm.c b/bfd/elf32-arm.c
> >> index
> >> 639fe0f125688ccf218b449467c746686841386f..e6afb99512524ac26c0e3842e8dbe29
> >> 3c
> >> 58bacad 100644 --- a/bfd/elf32-arm.c
> >> +++ b/bfd/elf32-arm.c
> >> @@ -5031,6 +5031,103 @@ cortex_a8_erratum_scan (bfd *input_bfd,
> >> 
> >>    return FALSE;
> >>  
> >>  }
> >> 
> >> +/* Create or update a stub entry depending on whether the stub can
> >> already
> >> be +   found in HTAB.  The stub is identified by:
> >> +   - its type STUB_TYPE
> >> +   - its source branch (note that several can share the same stub) whose
> >> +     section and relocation (if any) are given by SECTION and IRELA
> >> +     respectively
> >> +   - its target symbol whose input section, hash, name, value and branch
> >> type +     are given in SYM_SEC, HASH, SYM_NAME, SYM_VALUE and
> >> BRANCH_TYPE
> >> +     respectively
> >> +
> >> +   If found, the value of the stub's target symbol is updated from
> >> SYM_VALUE +   and *NEW_STUB is set to FALSE.  Otherwise, *NEW_STUB is set
> >> to +   TRUE and the stub entry is initialized.
> >> +
> >> +   Returns whether the stub could be successfully created or updated, or
> >> FALSE +   if an error occured.  */
> >> +
> >> +static bfd_boolean
> >> +elf32_arm_create_stub (struct elf32_arm_link_hash_table *htab,
> >> +                    enum elf32_arm_stub_type stub_type, asection
> >> *section,
> >> +                    Elf_Internal_Rela *irela, asection *sym_sec,
> >> +                    struct elf32_arm_link_hash_entry *hash, char
> >> *sym_name, +                    bfd_vma sym_value, enum
> >> arm_st_branch_type branch_type, +                    bfd_boolean
> >> *new_stub)
> >> +{
> >> +  const asection *id_sec;
> >> +  char *stub_name;
> >> +  struct elf32_arm_stub_hash_entry *stub_entry;
> >> +  unsigned int r_type;
> >> +
> >> +  BFD_ASSERT (stub_type != arm_stub_none);
> >> +  *new_stub = FALSE;
> >> +
> >> +  BFD_ASSERT (irela);
> >> +  BFD_ASSERT (section);
> >> +
> >> +  /* Support for grouping stub sections.  */
> >> +  id_sec = htab->stub_group[section->id].link_sec;
> >> +
> >> +  /* Get the name of this stub.  */
> >> +  stub_name = elf32_arm_stub_name (id_sec, sym_sec, hash, irela,
> >> stub_type); +  if (!stub_name)
> >> +    return FALSE;
> >> +
> >> +  stub_entry = arm_stub_hash_lookup (&htab->stub_hash_table, stub_name,
> >> FALSE, +                                   FALSE);
> >> +  /* The proper stub has already been created, just update its value. 
> >> */
> >> +  if (stub_entry != NULL)
> >> +    {
> >> +      free (stub_name);
> >> +      stub_entry->target_value = sym_value;
> >> +      return TRUE;
> >> +    }
> >> +
> >> +  stub_entry = elf32_arm_add_stub (stub_name, section, htab);
> >> +  if (stub_entry == NULL)
> >> +    {
> >> +      free (stub_name);
> >> +      return FALSE;
> >> +    }
> >> +
> >> +  stub_entry->target_value = sym_value;
> >> +  stub_entry->target_section = sym_sec;
> >> +  stub_entry->stub_type = stub_type;
> >> +  stub_entry->h = hash;
> >> +  stub_entry->branch_type = branch_type;
> >> +
> >> +  if (sym_name == NULL)
> >> +    sym_name = "unnamed";
> >> +  stub_entry->output_name = (char *)
> >> +    bfd_alloc (htab->stub_bfd, sizeof (THUMB2ARM_GLUE_ENTRY_NAME)
> >> +                             + strlen (sym_name));
> >> +  if (stub_entry->output_name == NULL)
> >> +    {
> >> +      free (stub_name);
> >> +      return FALSE;
> >> +    }
> >> +
> >> +  /* For historical reasons, use the existing names for ARM-to-Thumb and
> >> +     Thumb-to-ARM stubs.  */
> >> +  r_type = ELF32_R_TYPE (irela->r_info);
> >> +  if ((r_type == (unsigned int) R_ARM_THM_CALL
> >> +      || r_type == (unsigned int) R_ARM_THM_JUMP24
> >> +      || r_type == (unsigned int) R_ARM_THM_JUMP19)
> >> +      && branch_type == ST_BRANCH_TO_ARM)
> >> +    sprintf (stub_entry->output_name, THUMB2ARM_GLUE_ENTRY_NAME,
> >> sym_name); +  else if ((r_type == (unsigned int) R_ARM_CALL
> >> +          || r_type == (unsigned int) R_ARM_JUMP24)
> >> +         && branch_type == ST_BRANCH_TO_THUMB)
> >> +    sprintf (stub_entry->output_name, ARM2THUMB_GLUE_ENTRY_NAME,
> >> sym_name); +  else
> >> +    sprintf (stub_entry->output_name, STUB_ENTRY_NAME, sym_name);
> >> +
> >> +  *new_stub = TRUE;
> >> +  return TRUE;
> >> +}
> >> +
> >> 
> >>  /* 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
> >> 
> >> @@ -5174,14 +5271,11 @@ elf32_arm_size_stubs (bfd *output_bfd,
> >> 
> >>               {
> >>               
> >>                 unsigned int r_type, r_indx;
> >>                 enum elf32_arm_stub_type stub_type;
> >> 
> >> -               struct elf32_arm_stub_hash_entry *stub_entry;
> >> 
> >>                 asection *sym_sec;
> >>                 bfd_vma sym_value;
> >>                 bfd_vma destination;
> >>                 struct elf32_arm_link_hash_entry *hash;
> >>                 const char *sym_name;
> >> 
> >> -               char *stub_name;
> >> -               const asection *id_sec;
> >> 
> >>                 unsigned char st_type;
> >>                 enum arm_st_branch_type branch_type;
> >>                 bfd_boolean created_stub = FALSE;
> >> 
> >> @@ -5364,6 +5458,8 @@ elf32_arm_size_stubs (bfd *output_bfd,
> >> 
> >>                 do
> >>                 
> >>                   {
> >> 
> >> +                   bfd_boolean new_stub;
> >> +
> >> 
> >>                     /* Determine what (if any) linker stub is needed.  */
> >>                     stub_type = arm_type_of_stub (info, section, irela,
> >>                     
> >>                                                   st_type, &branch_type,
> >> 
> >> @@ -5372,74 +5468,21 @@ elf32_arm_size_stubs (bfd *output_bfd,
> >> 
> >>                     if (stub_type == arm_stub_none)
> >>                     
> >>                       break;
> >> 
> >> -                   /* Support for grouping stub sections.  */
> >> -                   id_sec = htab->stub_group[section->id].link_sec;
> >> -
> >> -                   /* Get the name of this stub.  */
> >> -                   stub_name = elf32_arm_stub_name (id_sec, sym_sec,
> >> hash,
> >> -                                                    irela, stub_type);
> >> -                   if (!stub_name)
> >> -                     goto error_ret_free_internal;
> >> -
> >> 
> >>                     /* We've either created a stub for this reloc
> >>                     already,
> >>                     
> >>                        or we are about to.  */
> >> 
> >> -                   created_stub = TRUE;
> >> -
> >> -                   stub_entry = arm_stub_hash_lookup
> >> -                                  (&htab->stub_hash_table, stub_name,
> >> -                                   FALSE, FALSE);
> >> -                   if (stub_entry != NULL)
> >> -                     {
> >> -                       /* The proper stub has already been created.  */
> >> -                       free (stub_name);
> >> -                       stub_entry->target_value = sym_value;
> >> -                       break;
> >> -                     }

Please take note of this lookup + conditional block.

> >> -
> >> -                   stub_entry = elf32_arm_add_stub (stub_name, section,
> >> -                                                    htab);
> >> -                   if (stub_entry == NULL)
> >> -                     {
> >> -                       free (stub_name);
> >> -                       goto error_ret_free_internal;
> >> -                     }
> >> +                   created_stub =
> >> +                     elf32_arm_create_stub (htab, stub_type, section,
> >> irela, +                                            sym_sec, hash,
> >> +                                            (char *) sym_name,
> >> sym_value,
> >> +                                            branch_type, &new_stub);
> >> 
> >> -                   stub_entry->target_value = sym_value;
> >> -                   stub_entry->target_section = sym_sec;
> >> -                   stub_entry->stub_type = stub_type;
> >> -                   stub_entry->h = hash;
> >> -                   stub_entry->branch_type = branch_type;
> >> -
> >> -                   if (sym_name == NULL)
> >> -                     sym_name = "unnamed";
> >> -                   stub_entry->output_name = (char *)
> >> -                       bfd_alloc (htab->stub_bfd,
> >> -                                  sizeof (THUMB2ARM_GLUE_ENTRY_NAME)
> >> -                                  + strlen (sym_name));
> >> -                   if (stub_entry->output_name == NULL)
> >> +                   if (!created_stub || !new_stub)
> 
> I'm not sure to understand why you check both?

Good catch! That's a result of the iterative process that for the create_stub 
function. It should be a break for the !new_stub case, as in the code I 
hilighted above.

I'll respin the patch.

Best regards,

Thomas
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