[PATCH 18/19 REVIEW] bfd: new functions for getting strings out of a strtab

[Nick Alcock <nick dot alcock at oracle dot com>]

The CTF linking process wants to deduplicate the CTF strtab against the
ELF strtab, for which it needs to know the number of strings in the
strtab and it needs to be able to extract them one by one.

The BFD strtab functions only support returning the
size-or-section-length of the strtab (with _bfd_elf_strtab_size)
and returning the offset (but not string!) and decrementing the refcount
at the same time.

So add new functions _bfd_elf_strtab_len (that just returns the length
in strings of the strtab, never the section size) and bfd_elf_strtab_str
(which returns the string at a given strtab index, and its offset,
without touching the refcount).

It is probably a mistake to use _bfd_elf_strtab_str in particular before
_bfd_elf_strtab_finalize is called, and will not produce useful output
if you do so.

bfd/
	* elf-strtab.c (_bfd_elf_strtab_len): New.
	(_bfd_elf_strtab_str): Likewise.
	* bfd-elf.h: Declare them.
---
 bfd/elf-bfd.h    |  4 ++++
 bfd/elf-strtab.c | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+)

The bfd bits of this need review, but I hope they will be uncontroversial.
There is no intent to use them to do evil things with string tables, only
to see what is there once ld has laid it out, without being forced to modify
its refcounts in the process.  (See the next commit for its use.)

diff --git a/bfd/elf-bfd.h b/bfd/elf-bfd.h
index 00443e6089..26f35a0f8a 100644
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -2237,8 +2237,12 @@ extern void _bfd_elf_strtab_restore
   (struct elf_strtab_hash *, void *);
 extern bfd_size_type _bfd_elf_strtab_size
   (struct elf_strtab_hash *);
+extern bfd_size_type _bfd_elf_strtab_len
+  (struct elf_strtab_hash *);
 extern bfd_size_type _bfd_elf_strtab_offset
   (struct elf_strtab_hash *, size_t);
+extern const char * _bfd_elf_strtab_str
+  (struct elf_strtab_hash *, size_t idx, size_t *offset);
 extern bfd_boolean _bfd_elf_strtab_emit
   (bfd *, struct elf_strtab_hash *);
 extern void _bfd_elf_strtab_finalize
diff --git a/bfd/elf-strtab.c b/bfd/elf-strtab.c
index ec9002fae7..5d3eac7b40 100644
--- a/bfd/elf-strtab.c
+++ b/bfd/elf-strtab.c
@@ -270,6 +270,12 @@ _bfd_elf_strtab_size (struct elf_strtab_hash *tab)
   return tab->sec_size ? tab->sec_size : tab->size;
 }
 
+bfd_size_type
+_bfd_elf_strtab_len (struct elf_strtab_hash *tab)
+{
+  return tab->size;
+}
+
 bfd_size_type
 _bfd_elf_strtab_offset (struct elf_strtab_hash *tab, size_t idx)
 {
@@ -285,6 +291,19 @@ _bfd_elf_strtab_offset (struct elf_strtab_hash *tab, size_t idx)
   return tab->array[idx]->u.index;
 }
 
+const char *
+_bfd_elf_strtab_str (struct elf_strtab_hash *tab, size_t idx,
+                     bfd_size_type *offset)
+{
+  if (idx == 0)
+    return 0;
+  BFD_ASSERT (idx < tab->size);
+  BFD_ASSERT (tab->sec_size);
+  if (offset)
+    *offset = tab->array[idx]->u.index;
+  return tab->array[idx]->root.string;
+}
+
 bfd_boolean
 _bfd_elf_strtab_emit (register bfd *abfd, struct elf_strtab_hash *tab)
 {
-- 
2.22.0.238.g049a27acdc