[rfc] .gdb_index: Fix crash on NULL psymtab

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

Hi,

this patch was created by a mistake, at least Fedora runs first gdb-add-index
and only then dwz is run, in such case this bug does not reproduce.

But when one runs dwz first and then gdb-add-index current GDB may crash.
Testcase is not posted here as I have not found a small reproducer and a full
reproducer is pretty big (230KB):
	http://people.redhat.com/jkratoch/unusedcu.patch

The reproducer crashes GDB although it does not produce valid result as with
dwz first and gdb-add-index second objcopy fails to complete the operation:
	BFD: stkYdQ3W: Not enough room for program headers, try linking with -N
	objcopy:stkYdQ3W[.note.ABI-tag]: Bad value
	BFD: stkYdQ3W: Not enough room for program headers, try linking with -N
	objcopy:stkYdQ3W[.gdb_index]: Bad value
	BFD: stkYdQ3W: Not enough room for program headers, try linking with -N
	objcopy:stkYdQ3W: Bad value

While it has currently no practical usefulness it fixes a GDB crash and IMO it
is even correct, OK to check-in, Tom?  It cannot regress just maybe one could
also print an error() in such case.


Thanks,
Jan


gdb/
2013-06-09  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* dwarf2read.c (write_psymtabs_to_index): Ignore NULL PSYMTAB.

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 55b1b17..09d7f7a 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -21261,6 +21261,12 @@ write_psymtabs_to_index (struct objfile *objfile, const char *dir)
       struct psymtab_cu_index_map *map;
       void **slot;
 
+      /* CU of a shared file from 'dwz -m' may be unused by this main file.
+	 It may be referenced from a local scope but in such case it does not
+	 need to be present in .gdb_index.  */
+      if (psymtab == NULL)
+	continue;
+
       if (psymtab->user == NULL)
 	recursively_write_psymbols (objfile, psymtab, symtab, psyms_seen, i);