gdb: change value_of_register and value_of_register_lazy to take the next frame

Some functions related to the handling of registers in frames accept
"this frame", for which we want to read or write the register values,
while other functions accept "the next frame", which is the frame next
to that.  The later is needed because we sometimes need to read register
values for a frame that does not exist yet (usually when trying to
unwind that frame-to-be).

value_of_register and value_of_register_lazy both take "this frame",
even if what they ultimately want internally is "the next frame".  This
is annoying if you are in a spot that currently has "the next frame" and
need to call one of these functions (which happens later in this
series).  You need to get the previous frame only for those functions to
get the next frame again.  This is more manipulations, more chances of
mistake.

I propose to change these functions (and a few more functions in the
subsequent patches) to operate on "the next frame".  Things become a bit
less awkward when all these functions agree on which frame they take.

So, in this patch, change value_of_register_lazy and value_of_register
to take "the next frame" instead of "this frame".  This adds a lot of
get_next_frame_sentinel_okay, but if we convert the user registers API
to also use "the next frame" instead of "this frame", it will get simple
again.

Change-Id: Iaa24815e648fbe5ae3c214c738758890a91819cd
Reviewed-By: John Baldwin <jhb@FreeBSD.org>

gdb/aarch64-tdep.c

@@ -3449,9 +3449,8 @@ value_of_aarch64_user_reg (frame_info_ptr frame, const void *baton)
 {
   const int *reg_p = (const int *) baton;
 
-  return value_of_register (*reg_p, frame);
+  return value_of_register (*reg_p, get_next_frame_sentinel_okay (frame));
 }
-
 
 /* Implement the "software_single_step" gdbarch method, needed to
    single step through atomic sequences on AArch64.  */

gdb/arm-tdep.c

@@ -9954,9 +9954,9 @@ static struct value *
 value_of_arm_user_reg (frame_info_ptr frame, const void *baton)
 {
   const int *reg_p = (const int *) baton;
-  return value_of_register (*reg_p, frame);
+  return value_of_register (*reg_p, get_next_frame_sentinel_okay (frame));
 }
-
+
 static enum gdb_osabi
 arm_elf_osabi_sniffer (bfd *abfd)
 {

gdb/eval.c

@@ -1134,7 +1134,8 @@ eval_op_register (struct type *expect_type, struct expression *exp,
       && regno < gdbarch_num_cooked_regs (exp->gdbarch))
     val = value::zero (register_type (exp->gdbarch, regno), not_lval);
   else
-    val = value_of_register (regno, get_selected_frame (NULL));
+    val = value_of_register
+      (regno, get_next_frame_sentinel_okay (get_selected_frame ()));
   if (val == NULL)
     error (_("Value of register %s not available."), name);
   else

gdb/findvar.c

@@ -243,42 +243,32 @@ copy_integer_to_size (gdb_byte *dest, int dest_size, const gdb_byte *source,
     }
 }
 
-/* Return a `value' with the contents of (virtual or cooked) register
-   REGNUM as found in the specified FRAME.  The register's type is
-   determined by register_type ().  */
+/* See value.h.  */
 
-struct value *
-value_of_register (int regnum, frame_info_ptr frame)
+value *
+value_of_register (int regnum, frame_info_ptr next_frame)
 {
-  struct gdbarch *gdbarch = get_frame_arch (frame);
-  struct value *reg_val;
+  gdbarch *gdbarch = frame_unwind_arch (next_frame);
 
   /* User registers lie completely outside of the range of normal
      registers.  Catch them early so that the target never sees them.  */
   if (regnum >= gdbarch_num_cooked_regs (gdbarch))
-    return value_of_user_reg (regnum, frame);
+    return value_of_user_reg (regnum, get_prev_frame_always (next_frame));
 
-  reg_val = value_of_register_lazy (frame, regnum);
+  value *reg_val = value_of_register_lazy (next_frame, regnum);
   reg_val->fetch_lazy ();
   return reg_val;
 }
 
-/* Return a `value' with the contents of (virtual or cooked) register
-   REGNUM as found in the specified FRAME.  The register's type is
-   determined by register_type ().  The value is not fetched.  */
+/* See value.h.  */
 
-struct value *
-value_of_register_lazy (frame_info_ptr frame, int regnum)
+value *
+value_of_register_lazy (frame_info_ptr next_frame, int regnum)
 {
-  struct gdbarch *gdbarch = get_frame_arch (frame);
-  struct value *reg_val;
-  frame_info_ptr next_frame;
+  gdbarch *gdbarch = frame_unwind_arch (next_frame);
 
   gdb_assert (regnum < gdbarch_num_cooked_regs (gdbarch));
-
-  gdb_assert (frame != NULL);
-
-  next_frame = get_next_frame_sentinel_okay (frame);
+  gdb_assert (next_frame != nullptr);
 
   /* In some cases NEXT_FRAME may not have a valid frame-id yet.  This can
      happen if we end up trying to unwind a register as part of the frame
@@ -291,7 +281,7 @@ value_of_register_lazy (frame_info_ptr frame, int regnum)
   /* We should have a valid next frame.  */
   gdb_assert (frame_id_p (get_frame_id (next_frame)));
 
-  reg_val = value::allocate_lazy (register_type (gdbarch, regnum));
+  value *reg_val = value::allocate_lazy (register_type (gdbarch, regnum));
   reg_val->set_lval (lval_register);
   VALUE_REGNUM (reg_val) = regnum;
   VALUE_NEXT_FRAME_ID (reg_val) = get_frame_id (next_frame);

gdb/frame-unwind.c

@@ -278,7 +278,8 @@ struct value *
 frame_unwind_got_register (frame_info_ptr frame,
 			   int regnum, int new_regnum)
 {
-  return value_of_register_lazy (frame, new_regnum);
+  return value_of_register_lazy (get_next_frame_sentinel_okay (frame),
+				 new_regnum);
 }
 
 /* Return a value which indicates that FRAME saved REGNUM in memory at

gdb/guile/scm-frame.c

@@ -835,7 +835,8 @@ gdbscm_frame_read_register (SCM self, SCM register_scm)
 						register_str,
 						strlen (register_str));
 	  if (regnum >= 0)
-	    value = value_of_register (regnum, frame);
+	    value = value_of_register (regnum,
+				       get_next_frame_sentinel_okay (frame));
 	}
     }
   catch (const gdb_exception &ex)

gdb/infcmd.c

@@ -2280,9 +2280,9 @@ default_print_registers_info (struct gdbarch *gdbarch,
       if (*(gdbarch_register_name (gdbarch, i)) == '\0')
 	continue;
 
-      default_print_one_register_info (file,
-				       gdbarch_register_name (gdbarch, i),
-				       value_of_register (i, frame));
+      default_print_one_register_info
+	(file, gdbarch_register_name (gdbarch, i),
+	 value_of_register (i, get_next_frame_sentinel_okay (frame)));
     }
 }
 

gdb/loongarch-tdep.c

@@ -392,7 +392,8 @@ loongarch_software_single_step (struct regcache *regcache)
 static struct value *
 value_of_loongarch_user_reg (frame_info_ptr frame, const void *baton)
 {
-  return value_of_register ((long long) baton, frame);
+  return value_of_register ((long long) baton,
+			    get_next_frame_sentinel_okay (frame));
 }
 
 /* Implement the frame_align gdbarch method.  */

gdb/mi/mi-main.c

@@ -1101,7 +1101,8 @@ output_register (frame_info_ptr frame, int regnum, int format,
 		 int skip_unavailable)
 {
   struct ui_out *uiout = current_uiout;
-  struct value *val = value_of_register (regnum, frame);
+  value *val
+    = value_of_register (regnum, get_next_frame_sentinel_okay (frame));
   struct value_print_options opts;
 
   if (skip_unavailable && !val->entirely_available ())

gdb/mips-tdep.c

@@ -8074,7 +8074,7 @@ static struct value *
 value_of_mips_user_reg (frame_info_ptr frame, const void *baton)
 {
   const int *reg_p = (const int *) baton;
-  return value_of_register (*reg_p, frame);
+  return value_of_register (*reg_p, get_next_frame_sentinel_okay (frame));
 }
 
 static struct gdbarch *

gdb/nds32-tdep.c

@@ -267,9 +267,10 @@ static const struct
 static struct value *
 value_of_nds32_reg (frame_info_ptr frame, const void *baton)
 {
-  return value_of_register ((int) (intptr_t) baton, frame);
+  return value_of_register ((int) (intptr_t) baton,
+			    get_next_frame_sentinel_okay (frame));
 }
-
+
 /* Implement the "frame_align" gdbarch method.  */
 
 static CORE_ADDR

gdb/python/py-frame.c

@@ -260,7 +260,8 @@ frapy_read_register (PyObject *self, PyObject *args, PyObject *kw)
 	return nullptr;
 
       gdb_assert (regnum >= 0);
-      struct value *val = value_of_register (regnum, frame);
+      value *val
+	= value_of_register (regnum, get_next_frame_sentinel_okay (frame));
 
       if (val == NULL)
 	PyErr_SetString (PyExc_ValueError, _("Can't read register."));

gdb/python/py-unwind.c

@@ -467,8 +467,8 @@ pending_framepy_read_register (PyObject *self, PyObject *args, PyObject *kw)
 	 which maps to a real register.  In the past,
 	 get_frame_register_value() was used here, which did not
 	 handle the user register case.  */
-      struct value *val = value_of_register (regnum,
-					     pending_frame->frame_info);
+      value *val = value_of_register
+        (regnum, get_next_frame_sentinel_okay (pending_frame->frame_info));
       if (val == NULL)
 	PyErr_Format (PyExc_ValueError,
 		      "Cannot read register %d from frame.",

gdb/riscv-tdep.c

@@ -168,7 +168,7 @@ static struct value *
 value_of_riscv_user_reg (frame_info_ptr frame, const void *baton)
 {
   const int *reg_p = (const int *) baton;
-  return value_of_register (*reg_p, frame);
+  return value_of_register (*reg_p, get_next_frame_sentinel_okay (frame));
 }
 
 /* Information about a register alias that needs to be set up for this
@@ -1149,7 +1149,7 @@ riscv_print_one_register_info (struct gdbarch *gdbarch,
 
   try
     {
-      val = value_of_register (regnum, frame);
+      val = value_of_register (regnum, get_next_frame_sentinel_okay (frame));
       regtype = val->type ();
     }
   catch (const gdb_exception_error &ex)

gdb/s12z-tdep.c

@@ -494,7 +494,7 @@ s12z_print_ccw_info (struct gdbarch *gdbarch,
 		     frame_info_ptr frame,
 		     int reg)
 {
-  struct value *v = value_of_register (reg, frame);
+  value *v = value_of_register (reg, get_next_frame_sentinel_okay (frame));
   const char *name = gdbarch_register_name (gdbarch, reg);
   uint32_t ccw = value_as_long (v);
   gdb_puts (name, file);

gdb/std-regs.c

@@ -39,7 +39,7 @@ value_of_builtin_frame_fp_reg (frame_info_ptr frame, const void *baton)
        register can do so by adding "fp" to register name table (mind
        you, doing this is probably a dangerous thing).  */
     return value_of_register (gdbarch_deprecated_fp_regnum (gdbarch),
-			      frame);
+			      get_next_frame_sentinel_okay (frame));
   else
     {
       struct type *data_ptr_type = builtin_type (gdbarch)->builtin_data_ptr;
@@ -58,7 +58,8 @@ value_of_builtin_frame_pc_reg (frame_info_ptr frame, const void *baton)
   struct gdbarch *gdbarch = get_frame_arch (frame);
 
   if (gdbarch_pc_regnum (gdbarch) >= 0)
-    return value_of_register (gdbarch_pc_regnum (gdbarch), frame);
+    return value_of_register (gdbarch_pc_regnum (gdbarch),
+			      get_next_frame_sentinel_okay (frame));
   else
     {
       struct type *func_ptr_type = builtin_type (gdbarch)->builtin_func_ptr;
@@ -77,7 +78,8 @@ value_of_builtin_frame_sp_reg (frame_info_ptr frame, const void *baton)
   struct gdbarch *gdbarch = get_frame_arch (frame);
 
   if (gdbarch_sp_regnum (gdbarch) >= 0)
-    return value_of_register (gdbarch_sp_regnum (gdbarch), frame);
+    return value_of_register (gdbarch_sp_regnum (gdbarch),
+			      get_next_frame_sentinel_okay (frame));
   error (_("Standard register ``$sp'' is not available for this target"));
 }
 
@@ -87,7 +89,8 @@ value_of_builtin_frame_ps_reg (frame_info_ptr frame, const void *baton)
   struct gdbarch *gdbarch = get_frame_arch (frame);
 
   if (gdbarch_ps_regnum (gdbarch) >= 0)
-    return value_of_register (gdbarch_ps_regnum (gdbarch), frame);
+    return value_of_register (gdbarch_ps_regnum (gdbarch),
+			      get_next_frame_sentinel_okay (frame));
   error (_("Standard register ``$ps'' is not available for this target"));
 }
 

gdb/value.h

@@ -1123,9 +1123,14 @@ extern struct value *value_of_variable (struct symbol *var,
 extern struct value *address_of_variable (struct symbol *var,
 					  const struct block *b);
 
-extern struct value *value_of_register (int regnum, frame_info_ptr frame);
+/* Return a value with the contents of register REGNUM as found in the frame
+   previous to NEXT_FRAME.  */
 
-struct value *value_of_register_lazy (frame_info_ptr frame, int regnum);
+extern value *value_of_register (int regnum, frame_info_ptr next_frame);
+
+/* Same as the above, but the value is not fetched.  */
+
+extern value *value_of_register_lazy (frame_info_ptr next_frame, int regnum);
 
 /* Return the symbol's reading requirement.  */