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

Mark Wielaard
2014-12-04T13:26:35Z

On Thu, 2014-11-27 at 15:53 +0100, Mark Wielaard wrote:
> 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?

Ping.

> 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. */
>