Skip unwritable frames in command "finish"

Nowadays, GDB can't insert breakpoint on the return address of the
exception handler on ARM M-profile, because the address is a magic
one 0xfffffff9,

 (gdb) bt
 #0  CT32B1_IRQHandler () at ../src/timer.c:67
 #1  <signal handler called>
 #2  main () at ../src/timer.c:127

(gdb) info frame
Stack level 0, frame at 0x200ffa8:
 pc = 0x4ec in CT32B1_IRQHandler (../src/timer.c:67); saved pc = 0xfffffff9
 called by frame at 0x200ffc8
 source language c.
 Arglist at 0x200ffa0, args:
 Locals at 0x200ffa0, Previous frame's sp is 0x200ffa8
 Saved registers:
  r7 at 0x200ffa0, lr at 0x200ffa4

(gdb) x/x 0xfffffff9
0xfffffff9:     Cannot access memory at address 0xfffffff9

(gdb) finish
Run till exit from #0  CT32B1_IRQHandler () at ../src/timer.c:67
Ed:15: Target error from Set break/watch: Et:96: Pseudo-address (0xFFFFFFxx) for EXC_RETURN is invalid (GDB error?)

Warning:
Cannot insert hardware breakpoint 0.
Could not insert hardware breakpoints:
You may have requested too many hardware breakpoints/watchpoints.

Command aborted.

even some debug probe can't set hardware breakpoint on the magic
address too,

(gdb) hbreak *0xfffffff9
Hardware assisted breakpoint 2 at 0xfffffff9
(gdb) c
Continuing.
Ed:15: Target error from Set break/watch: Et:96: Pseudo-address (0xFFFFFFxx) for EXC_RETURN is invalid (GDB error?)

Warning:
Cannot insert hardware breakpoint 2.
Could not insert hardware breakpoints:
You may have requested too many hardware breakpoints/watchpoints.

Command aborted.

The problem described above is quite similar to PR 8841, in which GDB
can't set breakpoint on signal trampoline, which is mapped to a read-only
page by kernel.  The rationale of this patch is to skip "unwritable"
frames when looking for caller frames in command "finish", and a new
gdbarch method code_of_frame_writable is added.  This patch fixes
the problem on ARM cortex-m target, but it can be used to fix
PR 8841 too.

gdb:

2016-05-10  Yao Qi  <yao.qi@arm.com>

	* arch-utils.c (default_code_of_frame_writable): New function.
	* arch-utils.h (default_code_of_frame_writable): Declare.
	* arm-tdep.c (arm_code_of_frame_writable): New function.
	(arm_gdbarch_init): Install gdbarch method
	code_of_frame_writable if the target is M-profile.
	* frame.c (skip_unwritable_frames): New function.
	* frame.h (skip_unwritable_frames): Declare.
	* gdbarch.sh (code_of_frame_writable): New.
	* gdbarch.c, gdbarch.h: Re-generated.
	* infcmd.c (finish_command): Call skip_unwritable_frames.

1 files changed, 23 insertions, 0 deletions

diff --git a/gdb/gdbarch.c b/gdb/gdbarch.c
index bd0b48c..313502b 100644
--- a/gdb/gdbarch.c
+++ b/gdb/gdbarch.c
@@ -205,6 +205,7 @@ struct gdbarch
   gdbarch_push_dummy_call_ftype *push_dummy_call;
   int call_dummy_location;
   gdbarch_push_dummy_code_ftype *push_dummy_code;
+  gdbarch_code_of_frame_writable_ftype *code_of_frame_writable;
   gdbarch_print_registers_info_ftype *print_registers_info;
   gdbarch_print_float_info_ftype *print_float_info;
   gdbarch_print_vector_info_ftype *print_vector_info;
@@ -387,6 +388,7 @@ gdbarch_alloc (const struct gdbarch_info *info,
   gdbarch->dwarf2_reg_to_regnum = no_op_reg_to_regnum;
   gdbarch->deprecated_fp_regnum = -1;
   gdbarch->call_dummy_location = AT_ENTRY_POINT;
+  gdbarch->code_of_frame_writable = default_code_of_frame_writable;
   gdbarch->print_registers_info = default_print_registers_info;
   gdbarch->print_float_info = default_print_float_info;
   gdbarch->register_sim_regno = legacy_register_sim_regno;
@@ -552,6 +554,7 @@ verify_gdbarch (struct gdbarch *gdbarch)
   /* Skip verify of push_dummy_call, has predicate.  */
   /* Skip verify of call_dummy_location, invalid_p == 0 */
   /* Skip verify of push_dummy_code, has predicate.  */
+  /* Skip verify of code_of_frame_writable, invalid_p == 0 */
   /* Skip verify of print_registers_info, invalid_p == 0 */
   /* Skip verify of print_float_info, invalid_p == 0 */
   /* Skip verify of print_vector_info, has predicate.  */
@@ -804,6 +807,9 @@ gdbarch_dump (struct gdbarch *gdbarch, struct ui_file *file)
                       "gdbarch_dump: char_signed = %s\n",
                       plongest (gdbarch->char_signed));
   fprintf_unfiltered (file,
+                      "gdbarch_dump: code_of_frame_writable = <%s>\n",
+                      host_address_to_string (gdbarch->code_of_frame_writable));
+  fprintf_unfiltered (file,
                       "gdbarch_dump: coff_make_msymbol_special = <%s>\n",
                       host_address_to_string (gdbarch->coff_make_msymbol_special));
   fprintf_unfiltered (file,
@@ -2314,6 +2320,23 @@ set_gdbarch_push_dummy_code (struct gdbarch *gdbarch,
   gdbarch->push_dummy_code = push_dummy_code;
 }
 
+int
+gdbarch_code_of_frame_writable (struct gdbarch *gdbarch, struct frame_info *frame)
+{
+  gdb_assert (gdbarch != NULL);
+  gdb_assert (gdbarch->code_of_frame_writable != NULL);
+  if (gdbarch_debug >= 2)
+    fprintf_unfiltered (gdb_stdlog, "gdbarch_code_of_frame_writable called\n");
+  return gdbarch->code_of_frame_writable (gdbarch, frame);
+}
+
+void
+set_gdbarch_code_of_frame_writable (struct gdbarch *gdbarch,
+                                    gdbarch_code_of_frame_writable_ftype code_of_frame_writable)
+{
+  gdbarch->code_of_frame_writable = code_of_frame_writable;
+}
+
 void
 gdbarch_print_registers_info (struct gdbarch *gdbarch, struct ui_file *file, struct frame_info *frame, int regnum, int all)
 {