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

Pedro Alves
2014-12-04T14:02:30Z

Hi Mark,

Thanks for doing this.

On 11/27/2014 02:53 PM, 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)

I'd suggest making the warnings a bit more consistent.

- "Warning." vs "warning: "

Prefer the latter, as that's what the "warning" function uses.

- "." vs "!"

I'd keep it calm and get rid of the "!". :-)

>
> 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.

I wonder if we could have a test? Could e.g., make sure we don't
crash when the user confirms a return in a noreturn function.

> 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))

if (attr != NULL && (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. */

> --- 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 "));
> + }

No space between "!" and query:

&& !query ...

> --- 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!");

i18n / _() .

Thanks,
Pedro Alves