[PATCH v5 02/12] BFD/aout: Sanitize back end flavour for external symbols retrieval

[Maciej W. Rozycki]

From: Maciej W. Rozycki <macro@redhat.com>

Make `aout_get_external_symbols' return unsuccessfully right away if 
called for a non-aout BFD, preventing a crash from an attempt to access 
inexistent ->tdata.aout_data->a (`struct aoutdata') struct member.  Add 
assertions at call sites to track potential invalid usage.

This converts a segmentation fault to an assertion failure followed by 
graceful termination:

.../ld/ld-new: BFD (GNU Binutils) 2.45.50.20251209 assertion fail .../bfd/aoutx.h:3449
.../ld/ld-new: tmpdir/ab.a: error adding symbols: file in wrong format

with an upcoming test case:

FAIL: CRIS regular archive link (implicit emulation)

where a `cris-aout' target linker invocation:

$ .../ld/ld-new -o tmpdir/abci -e ff tmpdir/abc.o tmpdir/ab.a

lands in `_bfd_generic_link_add_archive_symbols' with an inconsistent 
state between an archive's BFD and its member's BFD:

Breakpoint 1, _bfd_generic_link_add_archive_symbols (abfd=0x100264700,
    info=0x100253110 <link_info>,
    checkfn=0x10009ac80 <aout_link_check_archive_element>)
    at .../bfd/linker.c:1020
1020		  if (! (*checkfn) (element, info, h, arsym->name, &needed))
(gdb) print *abfd
$1 = {filename = 0x1002b6200 "tmpdir/ab.a",
  xvec = 0x10028d650 <cris_aout_vec>, iostream = 0x1002a47d0,
[...]
(gdb) print *element
$2 = {filename = 0x1002ccfb0 "a.o", xvec = 0x10028ea30 <cris_elf32_us_vec>,
  iostream = 0x0, iovec = 0x10028ace8 <cache_iovec>, lru_prev = 0x0,
[...]
(gdb) 
---
No change from v4 (04/14),
<https://inbox.sourceware.org/binutils/alpine.DEB.2.21.2601071848150.30566@angie.orcam.me.uk/>.

New change in v4.
---
 bfd/aoutx.h |   12 ++++++++++++
 bfd/pdp11.c |   12 ++++++++++++
 2 files changed, 24 insertions(+)

binutils-bfd-aout-get-external-symbols-assert.diff
Index: binutils-gdb/bfd/aoutx.h
===================================================================
--- binutils-gdb.orig/bfd/aoutx.h
+++ binutils-gdb/bfd/aoutx.h
@@ -1288,6 +1288,9 @@ NAME (aout, set_section_contents) (bfd *
 static bool
 aout_get_external_symbols (bfd *abfd)
 {
+  if (bfd_get_flavour (abfd) != bfd_target_aout_flavour)
+    return false;
+
   if (obj_aout_external_syms (abfd) == NULL)
     {
       bfd_size_type count;
@@ -1731,6 +1734,8 @@ NAME (aout, slurp_symbol_table) (bfd *ab
   aout_symbol_type *cached;
   bfd_size_type cached_size;
 
+  BFD_ASSERT (bfd_get_flavour (abfd) == bfd_target_aout_flavour);
+
   /* If there's no work to be done, don't do any.  */
   if (obj_aout_symbols (abfd) != NULL)
     return true;
@@ -2598,6 +2603,8 @@ NAME (aout, read_minisymbols) (bfd *abfd
 			       void * *minisymsp,
 			       unsigned int *sizep)
 {
+  BFD_ASSERT (bfd_get_flavour (abfd) == bfd_target_aout_flavour);
+
   if (dynamic)
     /* We could handle the dynamic symbols here as well, but it's
        easier to hand them off.  */
@@ -3215,6 +3222,8 @@ aout_link_free_symbols (bfd *abfd)
 static bool
 aout_link_add_object_symbols (bfd *abfd, struct bfd_link_info *info)
 {
+  BFD_ASSERT (bfd_get_flavour (abfd) == bfd_target_aout_flavour);
+
   if (! aout_get_external_symbols (abfd))
     return false;
   if (! aout_link_add_symbols (abfd, info))
@@ -3437,6 +3446,8 @@ aout_link_check_archive_element (bfd *ab
   bfd *oldbfd;
   bool needed;
 
+  BFD_ASSERT (bfd_get_flavour (abfd) == bfd_target_aout_flavour);
+
   if (!aout_get_external_symbols (abfd))
     return false;
 
@@ -5261,6 +5272,7 @@ static bool
 aout_link_input_bfd (struct aout_final_link_info *flaginfo, bfd *input_bfd)
 {
   BFD_ASSERT (bfd_get_format (input_bfd) == bfd_object);
+  BFD_ASSERT (bfd_get_flavour (input_bfd) == bfd_target_aout_flavour);
 
   /* If this is a dynamic object, it may need special handling.  */
   if ((input_bfd->flags & DYNAMIC) != 0
Index: binutils-gdb/bfd/pdp11.c
===================================================================
--- binutils-gdb.orig/bfd/pdp11.c
+++ binutils-gdb/bfd/pdp11.c
@@ -1264,6 +1264,9 @@ NAME (aout, set_section_contents) (bfd *
 static bool
 aout_get_external_symbols (bfd *abfd)
 {
+  if (bfd_get_flavour (abfd) != bfd_target_aout_flavour)
+    return false;
+
   if (obj_aout_external_syms (abfd) == NULL)
     {
       bfd_size_type count;
@@ -1604,6 +1607,8 @@ NAME (aout, slurp_symbol_table) (bfd *ab
   aout_symbol_type *cached;
   bfd_size_type cached_size;
 
+  BFD_ASSERT (bfd_get_flavour (abfd) == bfd_target_aout_flavour);
+
   /* If there's no work to be done, don't do any.  */
   if (obj_aout_symbols (abfd) != NULL)
     return true;
@@ -2235,6 +2240,8 @@ NAME (aout, read_minisymbols) (bfd *abfd
 			       void * *minisymsp,
 			       unsigned int *sizep)
 {
+  BFD_ASSERT (bfd_get_flavour (abfd) == bfd_target_aout_flavour);
+
   if (dynamic)
     /* We could handle the dynamic symbols here as well, but it's
        easier to hand them off.  */
@@ -2637,6 +2644,8 @@ NAME (aout, link_add_symbols) (bfd *abfd
 static bool
 aout_link_add_object_symbols (bfd *abfd, struct bfd_link_info *info)
 {
+  BFD_ASSERT (bfd_get_flavour (abfd) == bfd_target_aout_flavour);
+
   if (! aout_get_external_symbols (abfd))
     return false;
   if (! aout_link_add_symbols (abfd, info))
@@ -2801,6 +2810,8 @@ aout_link_check_archive_element (bfd *ab
   bfd *oldbfd;
   bool needed;
 
+  BFD_ASSERT (bfd_get_flavour (abfd) == bfd_target_aout_flavour);
+
   if (!aout_get_external_symbols (abfd))
     return false;
 
@@ -3698,6 +3709,7 @@ static bool
 aout_link_input_bfd (struct aout_final_link_info *flaginfo, bfd *input_bfd)
 {
   BFD_ASSERT (bfd_get_format (input_bfd) == bfd_object);
+  BFD_ASSERT (bfd_get_flavour (input_bfd) == bfd_target_aout_flavour);
 
   /* If this is a dynamic object, it may need special handling.  */
   if ((input_bfd->flags & DYNAMIC) != 0