[PATCH] gdb: skip objfiles with no BFD in DWARF unwinder

[Jan Vrany <jan.vrany@labware.com>]

While playing with JIT reader I experienced GDB to crash on null-pointer
dereference when stepping through non-jitted code.

The problem was that dwarf2_frame_find_fde () assumed that all objfiles
have BFD but that's not always true. To address this problem, this
commit skips such objfiles.

As for the test, I initially tried to use temporary breakpoint and then
'continue' to get out of the jitted code but this for some reason did
not trigger the crash. Using 'finish' to get out of jitted code followed
by 'next' triggered it.
---
 gdb/dwarf2/frame.c                    |  3 +++
 gdb/objfiles.h                        |  4 +++-
 gdb/testsuite/gdb.base/jit-reader.exp | 10 ++++++++++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
index 5878d72f922..514ae8c694f 100644
--- a/gdb/dwarf2/frame.c
+++ b/gdb/dwarf2/frame.c
@@ -1565,6 +1565,9 @@ dwarf2_frame_find_fde (CORE_ADDR *pc, dwarf2_per_objfile **out_per_objfile)
       CORE_ADDR offset;
       CORE_ADDR seek_pc;
 
+      if (objfile->obfd == nullptr)
+	continue;
+
       comp_unit *unit = find_comp_unit (objfile);
       if (unit == NULL)
 	{
diff --git a/gdb/objfiles.h b/gdb/objfiles.h
index 8bd76705688..429dea1da4c 100644
--- a/gdb/objfiles.h
+++ b/gdb/objfiles.h
@@ -636,7 +636,9 @@ struct objfile
   struct compunit_symtab *compunit_symtabs = nullptr;
 
   /* The object file's BFD.  Can be null if the objfile contains only
-     minimal symbols, e.g. the run time common symbols for SunOS4.  */
+     minimal symbols (e.g. the run time common symbols for SunOS4) or
+     if the objfile is a dynamic objfile (e.g. created by JIT reader
+     API).  */
 
   bfd *obfd;
 
diff --git a/gdb/testsuite/gdb.base/jit-reader.exp b/gdb/testsuite/gdb.base/jit-reader.exp
index d94360cd7d9..0de552b1ce5 100644
--- a/gdb/testsuite/gdb.base/jit-reader.exp
+++ b/gdb/testsuite/gdb.base/jit-reader.exp
@@ -271,6 +271,16 @@ proc jit_reader_test {} {
 		 "#1 ${any} in main ${any}" \
 		]
     }
+
+    # check that the DWARF unwinder does not crash in presence of
+    # JIT objfiles.
+    gdb_test "fin" \
+	[multi_line \
+		 "Run till exit from ${any} jit_function_stack_mangle ${any}" \
+		 "main ${any} at ${any}.*" \
+		]
+    gdb_test "bt" "#0  main ${any} at ${any}"
+    gdb_test "next"
 }
 
 jit_reader_test
-- 
2.35.1