[PATCH] Use GCC5/DWARF5 DW_AT_noreturn to mark functions that don't return normally.

[Mark Wielaard <mjw at redhat dot com>]

Add a flag field is_noreturn to struct func_type. Make calling_convention
a small bit field to not increase the size of the struct. Set is_noreturn
if the new GCC5/DWARF5 DW_AT_noreturn is set on a DW_TAG_subprogram.
Use this information to warn the user before doing a finish or return from
a function that does not return normally to its caller.

(gdb) finish
Warning. Function endless does not return normally.
Try to finish anyway? (y or n)

(gdb) return
warning: Function does not return normally to caller!
Make endless return now? (y or n)

gdb/ChangeLog

	* dwarf2read.c (read_subroutine_type): Set TYPE_NO_RETURN from
	DW_AT_noreturn.
	* gdbtypes.h (struct func_type): Add is_noreturn field flag. Make
	calling_convention an 8 bit bit field.
	(TYPE_NO_RETURN): New macro.
	* infcmd.c (finish_command): Query if function does not return
	normally.
	* stack.c (return_command): Likewise.

include/ChangeLog

	* dwarf2.def (DW_AT_noreturn): New DWARF5 attribute.

The dwarf2.h addition and the code to emit the new attribute is already in
the gcc tree.

OK to commit?

Thanks,

Mark

diff --git a/gdb/dwarf2read.c b/gdb/dwarf2read.c
index 36cbbd9..56212e5 100644
--- a/gdb/dwarf2read.c
+++ b/gdb/dwarf2read.c
@@ -14312,6 +14312,12 @@ read_subroutine_type (struct die_info *die, struct dwarf2_cu *cu)
   else
     TYPE_CALLING_CONVENTION (ftype) = DW_CC_normal;
 
+  /* Record whether the function returns normally to its caller or not
+     if the DWARF producer set that information.  */
+  attr = dwarf2_attr (die, DW_AT_noreturn, cu);
+  if (attr && (DW_UNSND (attr) != 0))
+    TYPE_NO_RETURN (ftype) = 1;
+
   /* We need to add the subroutine type to the die immediately so
      we don't infinitely recurse when dealing with parameters
      declared as the same subroutine type.  */
diff --git a/gdb/gdbtypes.h b/gdb/gdbtypes.h
index 14a1f08..779b728 100644
--- a/gdb/gdbtypes.h
+++ b/gdb/gdbtypes.h
@@ -1019,9 +1019,16 @@ struct func_type
   {
     /* * The calling convention for targets supporting multiple ABIs.
        Right now this is only fetched from the Dwarf-2
-       DW_AT_calling_convention attribute.  */
+       DW_AT_calling_convention attribute.  The value is one of the
+       DW_CC enum dwarf_calling_convention constants.  */
 
-    unsigned calling_convention;
+    unsigned calling_convention : 8;
+
+    /* * Whether this function normally returns to its caller.  It is
+       set from the DW_AT_noreturn attribute if set on the
+       DW_TAG_subprogram.  */
+
+    unsigned int is_noreturn : 1;
 
     /* * Only those DW_TAG_GNU_call_site's in this function that have
        DW_AT_GNU_tail_call set are linked in this list.  Function
@@ -1245,6 +1252,7 @@ extern void allocate_gnat_aux_type (struct type *);
 #define TYPE_GNAT_SPECIFIC(thistype) TYPE_MAIN_TYPE(thistype)->type_specific.gnat_stuff
 #define TYPE_DESCRIPTIVE_TYPE(thistype) TYPE_GNAT_SPECIFIC(thistype)->descriptive_type
 #define TYPE_CALLING_CONVENTION(thistype) TYPE_MAIN_TYPE(thistype)->type_specific.func_stuff->calling_convention
+#define TYPE_NO_RETURN(thistype) TYPE_MAIN_TYPE(thistype)->type_specific.func_stuff->is_noreturn
 #define TYPE_TAIL_CALL_LIST(thistype) TYPE_MAIN_TYPE(thistype)->type_specific.func_stuff->tail_call_list
 #define TYPE_BASECLASS(thistype,index) TYPE_FIELD_TYPE(thistype, index)
 #define TYPE_N_BASECLASSES(thistype) TYPE_CPLUS_SPECIFIC(thistype)->n_baseclasses
diff --git a/gdb/infcmd.c b/gdb/infcmd.c
index 4415b31..8231306 100644
--- a/gdb/infcmd.c
+++ b/gdb/infcmd.c
@@ -1869,7 +1869,14 @@ finish_command (char *arg, int from_tty)
       if (execution_direction == EXEC_REVERSE)
 	printf_filtered (_("Run back to call of "));
       else
-	printf_filtered (_("Run till exit from "));
+	{
+	  if (function != NULL && TYPE_NO_RETURN (function->type)
+	      && ! query (_("Warning. Function %s does not return normally.\n"
+			    "Try to finish anyway? "),
+			  SYMBOL_PRINT_NAME (function)))
+	    error (_("Not confirmed."));
+	  printf_filtered (_("Run till exit from "));
+	}
 
       print_stack_frame (get_selected_frame (NULL), 1, LOCATION, 0);
     }
diff --git a/gdb/stack.c b/gdb/stack.c
index 2834801..c753005 100644
--- a/gdb/stack.c
+++ b/gdb/stack.c
@@ -2462,8 +2462,12 @@ return_command (char *retval_exp, int from_tty)
 	confirmed = query (_("%sMake selected stack frame return now? "),
 			   query_prefix);
       else
-	confirmed = query (_("%sMake %s return now? "), query_prefix,
-			   SYMBOL_PRINT_NAME (thisfun));
+	{
+	  if (TYPE_NO_RETURN (thisfun->type))
+	    warning ("Function does not return normally to caller!");
+	  confirmed = query (_("%sMake %s return now? "), query_prefix,
+			     SYMBOL_PRINT_NAME (thisfun));
+	}
       if (!confirmed)
 	error (_("Not confirmed"));
     }
diff --git a/include/dwarf2.def b/include/dwarf2.def
index 8ca143c..8533a3e 100644
--- a/include/dwarf2.def
+++ b/include/dwarf2.def
@@ -308,6 +308,8 @@ DW_AT (DW_AT_data_bit_offset, 0x6b)
 DW_AT (DW_AT_const_expr, 0x6c)
 DW_AT (DW_AT_enum_class, 0x6d)
 DW_AT (DW_AT_linkage_name, 0x6e)
+/* DWARF 5.  */
+DW_AT (DW_AT_noreturn, 0x87)
 
 DW_AT_DUP (DW_AT_lo_user, 0x2000) /* Implementation-defined range start.  */
 DW_AT_DUP (DW_AT_hi_user, 0x3fff) /* Implementation-defined range end.  */