[RFC][PATCH] Fix AIX core file handling: prevent crashes during GDB quit

[Aditya Vidyadhar Kamath]

From: Aditya Vidyadhar Kamath <aditya.kamath1@ibm.com>

When quitting GDB after analyzing a core file, _bfd_coff_free_cached_info()
crashed with a segmentation fault. 

We can see this problem when quit after debugging a large core file
in AIX 7.3.

Ex:
Program terminated with signal SIGSEGV, Segmentation fault.
   from /opt/freeware/lib/libpython3.9.a(libpython3.9.so)
(gdb)q

Fatal signal: Segmentation fault
----- Backtrace -----
0x1009fbffb ???
0x1009fc11f ???
0x1005c3587 ???
0x1005c3833 ???
0x4fdf ???

The backtrace showed:

  htab_delete(0x0000bc18) at 0x1000e2e4
  _bfd_coff_free_cached_info(abfd = 0x20023a90) at 0xd02e5a58
  bfd_cache_close(abfd = 0x20023a90) at 0xd02c0e7c
  bfd_cache_close_all() at 0xd02c0f48
  bfd_close_all_done(abfd = 0x20023a90) at 0xd02c1234
  bfd_close(abfd = 0x20023a90) at 0xd02c1180

My understanding so is as follows:
1. AIX core files store a pointer to 'struct core_dumpxx' in abfd->tdata.any
2. COFF object files store a pointer to 'struct coff_data_type' in the same field
3. The condition checked: (bfd_get_format(abfd) == bfd_object ||
                            bfd_get_format(abfd) == bfd_core)
4. For core files, the code cast 'core_dumpxx *' to 'coff_data_type *'
5. It then tried to read 'section_by_target_index' hash table pointer
6. Reading from the wrong offset in core_dumpxx returned garbage (0xbc18)
7. This garbage pointer passed the NULL check but crashed in htab_delete()

I think the hash tables are only allocated when processing COFF symbols, which
   never happens for core files.

This patch is a fix to the same.
---
 bfd/coffgen.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/bfd/coffgen.c b/bfd/coffgen.c
index 030dbc1dc79..ca555647592 100644
--- a/bfd/coffgen.c
+++ b/bfd/coffgen.c
@@ -3310,8 +3310,7 @@ _bfd_coff_free_cached_info (bfd *abfd)
   struct coff_tdata *tdata;
 
   if (bfd_family_coff (abfd)
-      && (bfd_get_format (abfd) == bfd_object
-	  || bfd_get_format (abfd) == bfd_core)
+      && (bfd_get_format (abfd) == bfd_object)
       && (tdata = coff_data (abfd)) != NULL)
     {
       if (tdata->section_by_index)
-- 
2.41.0