opcodes/csky: return the default disassembler when there is no bfd

The disassembler function should return a valid disassembler function
even when there is no BFD present.  This is implied (I believe) by the
comment in dis-asm.h which says the BFD may be NULL.  Further, it
makes sense when considering that the disassembler is used in GDB, and
GDB may connect to a target and perform debugging even without a BFD
being supplied.

This commit makes the csky_get_disassembler function return the
default disassembler configuration when no bfd is supplied, this is
the same default configuration as is used when a BFD is supplied, but
the BFD has no attributes section.

Before the change configuring GDB with --enable-targets=all and
running the tests gdb.base/all-architectures-2.exp results in many
errors, but after this change there are no failures.

opcodes/ChangeLog:

	* csky-dis.c (csky_get_disassembler): Don't return NULL when there
	is no BFD.

opcodes/ChangeLog

@@ -1,3 +1,8 @@
+2020-09-16  Andrew Burgess <andrew.burgess@embecosm.com>
+
+	* csky-dis.c (csky_get_disassembler): Don't return NULL when there
+	is no BFD.
+
 2020-09-16  Alan Modra  <amodra@gmail.com>
 
 	* ppc-dis.c (ppc_symbol_is_valid): Adjust elf_symbol_from invocation.

opcodes/csky-dis.c

@@ -239,23 +239,25 @@ csky_get_disassembler (bfd *abfd)
   obj_attribute *attr;
   const char *sec_name = NULL;
   if (!abfd)
-    return NULL;
-
-  mach_flag = elf_elfheader (abfd)->e_flags;
-
-  sec_name = get_elf_backend_data (abfd)->obj_attrs_section;
-  /* Skip any input that hasn't attribute section.
-     This enables to link object files without attribute section with
-     any others.  */
-  if (bfd_get_section_by_name (abfd, sec_name) != NULL)
+    dis_info.isa = CSKY_DEFAULT_ISA;
+  else
     {
-      attr = elf_known_obj_attributes_proc (abfd);
-      dis_info.isa = attr[Tag_CSKY_ISA_EXT_FLAGS].i;
-      dis_info.isa <<= 32;
-      dis_info.isa |= attr[Tag_CSKY_ISA_FLAGS].i;
+      mach_flag = elf_elfheader (abfd)->e_flags;
+
+      sec_name = get_elf_backend_data (abfd)->obj_attrs_section;
+      /* Skip any input that hasn't attribute section.
+         This enables to link object files without attribute section with
+         any others.  */
+      if (bfd_get_section_by_name (abfd, sec_name) != NULL)
+        {
+          attr = elf_known_obj_attributes_proc (abfd);
+          dis_info.isa = attr[Tag_CSKY_ISA_EXT_FLAGS].i;
+          dis_info.isa <<= 32;
+          dis_info.isa |= attr[Tag_CSKY_ISA_FLAGS].i;
+        }
+      else
+        dis_info.isa = CSKY_DEFAULT_ISA;
     }
-  else
-    dis_info.isa = CSKY_DEFAULT_ISA;
 
    return print_insn_csky;
 }