arc: Select CPU model properly before disassembling

Enforce CPU model for disassembler via its options, if it was specified in XML
target description, otherwise use default method of determining CPU implemented
in disassembler - scanning ELF private header.  The latter requires
disassemble_info->section to be properly initialized.  To make sure that
info->section is set in all cases this patch partially reverts [1] for ARC: it
reinstates arc_delayed_print_insn as a "print_insn" function for ARC, but
now this function only sets disassemble_info->section and then calls
default_print_insn to do the rest of the job.

Support for CPU in disassembler options for ARC has been added in [2].

[1] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=39503f82427e22ed8e04d986ccdc8562091ec62e
[2] https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=10045478d984f9924cb945423388ba25b7dd3ffe

gdb/ChangeLog:

yyyy-mm-dd  Anton Kolesov  <anton.kolesov@synopsys.com>

	* arc-tdep.c (arc_disassembler_options): New variable.
	(arc_gdbarch_init): Set and use it. Use arc_delayed_print_insn instead
	of default_print_insn.
	(arc_delayed_print_insn): Set info->section when needed,
	use default_print_insn to retrieve a disassembler.

2 files changed, 65 insertions, 6 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 4274f3a..d6bd686 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,11 @@
+2017-06-16  Anton Kolesov  <anton.kolesov@synopsys.com>
+
+	* arc-tdep.c (arc_disassembler_options): New variable.
+	(arc_gdbarch_init): Set and use it. Use arc_delayed_print_insn instead
+	of default_print_insn.
+	(arc_delayed_print_insn): Set info->section when needed,
+	use default_print_insn to retrieve a disassembler.
+
 2017-06-14  Sergio Durigan Junior  <sergiodj@redhat.com>
 
 	PR gdb/21574
diff --git a/gdb/arc-tdep.c b/gdb/arc-tdep.c
index d9ee5c6..21f7015 100644
--- a/gdb/arc-tdep.c
+++ b/gdb/arc-tdep.c
@@ -145,6 +145,8 @@ static const char *const core_arcompact_register_names[] = {
   "lp_count", "reserved", "limm", "pcl",
 };
 
+static char *arc_disassembler_options = NULL;
+
 /* Functions are sorted in the order as they are used in the
    _initialize_arc_tdep (), which uses the same order as gdbarch.h.  Static
    functions are defined before the first invocation.  */
@@ -1405,12 +1407,34 @@ arc_skip_prologue (struct gdbarch *gdbarch, CORE_ADDR pc)
 int
 arc_delayed_print_insn (bfd_vma addr, struct disassemble_info *info)
 {
-  int (*print_insn) (bfd_vma, struct disassemble_info *);
-  /* exec_bfd may be null, if GDB is run without a target BFD file.  Opcodes
-     will handle NULL value gracefully.  */
-  print_insn = arc_get_disassembler (exec_bfd);
-  gdb_assert (print_insn != NULL);
-  return print_insn (addr, info);
+  /* Standard BFD "machine number" field allows libocodes disassembler to
+     distinguish ARC 600, 700 and v2 cores, however v2 encompasses both ARC EM
+     and HS, which have some difference between.  There are two ways to specify
+     what is the target core:
+     1) via the disassemble_info->disassembler_options;
+     2) otherwise libopcodes will use private (architecture-specific) ELF
+     header.
+
+     Using disassembler_options is preferable, because it comes directly from
+     GDBserver which scanned an actual ARC core identification info.  However,
+     not all GDBservers report core architecture, so as a fallback GDB still
+     should support analysis of ELF header.  The libopcodes disassembly code
+     uses the section to find the BFD and the BFD to find the ELF header,
+     therefore this function should set disassemble_info->section properly.
+
+     disassembler_options was already set by non-target specific code with
+     proper options obtained via gdbarch_disassembler_options ().
+
+     This function might be called multiple times in a sequence, reusing same
+     disassemble_info.  */
+  if ((info->disassembler_options == NULL) && (info->section == NULL))
+    {
+      struct obj_section *s = find_pc_section (addr);
+      if (s != NULL)
+	info->section = s->the_bfd_section;
+    }
+
+  return default_print_insn (addr, info);
 }
 
 /* Baremetal breakpoint instructions.
@@ -2013,6 +2037,8 @@ arc_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
 
   set_gdbarch_frame_align (gdbarch, arc_frame_align);
 
+  set_gdbarch_print_insn (gdbarch, arc_delayed_print_insn);
+
   set_gdbarch_cannot_step_breakpoint (gdbarch, 1);
 
   /* "nonsteppable" watchpoint means that watchpoint triggers before
@@ -2041,6 +2067,31 @@ arc_gdbarch_init (struct gdbarch_info info, struct gdbarch_list *arches)
   if (tdep->jb_pc >= 0)
     set_gdbarch_get_longjmp_target (gdbarch, arc_get_longjmp_target);
 
+  /* Disassembler options.  Enforce CPU if it was specified in XML target
+     description, otherwise use default method of determining CPU (ELF private
+     header).  */
+  if (info.target_desc != NULL)
+    {
+      const struct bfd_arch_info *tdesc_arch
+	= tdesc_architecture (info.target_desc);
+      if (tdesc_arch != NULL)
+	{
+	  xfree (arc_disassembler_options);
+	  /* FIXME: It is not really good to change disassembler options
+	     behind the scene, because that might override options
+	     specified by the user.  However as of now ARC doesn't support
+	     `set disassembler-options' hence this code is the only place
+	     where options are changed.  It also changes options for all
+	     existing gdbarches, which also can be problematic, if
+	     arc_gdbarch_init will start reusing existing gdbarch
+	     instances.  */
+	  arc_disassembler_options = xstrprintf ("cpu=%s",
+						 tdesc_arch->printable_name);
+	  set_gdbarch_disassembler_options (gdbarch,
+					    &arc_disassembler_options);
+	}
+    }
+
   tdesc_use_registers (gdbarch, tdesc, tdesc_data);
 
   return gdbarch;