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

Mark Wielaard
2014-11-27T14:53:23Z

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. */