[PATCH] gdb: care for dynamic objfiles in build_id_bfd_get ()

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

Accessing gdb.Objfile.build_id caused GDB to crash when objfile is
dynamic, that is created by JIT reader API. Similarly, invoking
gdb.Symtab.fullname() caused a crash. Possibly there are other paths
that may trigger the crash.

The issue was NULL-pointer dereferencing in build_id_bfd_get () because
dynamic objfiles have no underlaying BFD structure. This commit fixes
the problem by a NULL-check in build_id_bfd_get ().
---
 gdb/build-id.c                        | 6 ++++++
 gdb/testsuite/gdb.base/jit-reader.exp | 4 ++++
 2 files changed, 10 insertions(+)

diff --git a/gdb/build-id.c b/gdb/build-id.c
index c82f96402c8..671cbc1b545 100644
--- a/gdb/build-id.c
+++ b/gdb/build-id.c
@@ -32,6 +32,12 @@
 const struct bfd_build_id *
 build_id_bfd_get (bfd *abfd)
 {
+  /* Dynamic objfiles such as ones created by JIT reader API
+     have no underlaying bfd structure (that is, objfile->obfd
+     is NULL).  */
+  if (abfd == nullptr)
+    return NULL;
+
   if (!bfd_check_format (abfd, bfd_object)
       && !bfd_check_format (abfd, bfd_core))
     return NULL;
diff --git a/gdb/testsuite/gdb.base/jit-reader.exp b/gdb/testsuite/gdb.base/jit-reader.exp
index 5f8b6b0343c..d8d561cd4df 100644
--- a/gdb/testsuite/gdb.base/jit-reader.exp
+++ b/gdb/testsuite/gdb.base/jit-reader.exp
@@ -233,6 +233,10 @@ proc jit_reader_test {} {
 		gdb_test "python print(list(map(lambda objf : objf.filename, gdb.objfiles())))" \
 		    "$any'<< JIT compiled code at $hex >>'$any" \
 		    "python gdb.Objfile.filename"
+
+		gdb_test "python print( \[o for o in gdb.objfiles() if o.filename.startswith('<< JIT compiled code')\]\[0\].build_id )" \
+		    "None" \
+		    "python gdb.Objfile.build_id"
 	    }
 	}
     }
-- 
2.39.0