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Re: [PATCH] infcmd.c: Don't attempt to record a NULL value after a finish command
- From: Pedro Alves <palves at redhat dot com>
- To: Kevin Buettner <kevinb at redhat dot com>, gdb-patches at sourceware dot org
- Date: Wed, 30 Sep 2015 11:27:25 +0100
- Subject: Re: [PATCH] infcmd.c: Don't attempt to record a NULL value after a finish command
- Authentication-results: sourceware.org; auth=none
- References: <20150929214350 dot 44b076c7 at pinnacle dot lan>
On 09/30/2015 05:43 AM, Kevin Buettner wrote:
> Architectures which use RETURN_VALUE_STRUCT_CONVENTION will have a
> NULL return value after executing a finish command. See get_return_value()
> in infcmd.c.
>
> This patch avoids an eventual SIGSEV (caused by attempting to
> derefrence a NULL pointer) by adding a suitable test to
> finish_command_fsm_should_stop().
>
> I encountered this problem while testing msp430:
>
> (gdb) PASS: gdb.base/structs.exp: zed L<n> for finish; return 1 structs-tc
> finish
> Run till exit from #0 fun1 () at /ironwood1/sourceware-git/msp430-elf/../binutils-gdb/gdb/testsuite/gdb.base/structs.c:125
> ERROR: Process no longer exists
>
> gdb/ChangeLog:
> * infcmd.c (finish_command_fsm_should_stop): Don't attempt to
> record a NULL value.
> ---
> gdb/infcmd.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/gdb/infcmd.c b/gdb/infcmd.c
> index c4d7d8b..6be95e4 100644
> --- a/gdb/infcmd.c
> +++ b/gdb/infcmd.c
> @@ -1788,7 +1788,7 @@ finish_command_fsm_should_stop (struct thread_fsm *self)
> internal_error (__FILE__, __LINE__,
> _("finish_command: function has no target type"));
>
> - if (TYPE_CODE (rv->type) != TYPE_CODE_VOID)
> + if (rv->value != NULL && TYPE_CODE (rv->type) != TYPE_CODE_VOID)
> {
> struct value *func;
It's this else block that below sets rv->value in the first place:
if (TYPE_CODE (rv->type) != TYPE_CODE_VOID)
{
struct value *func;
func = read_var_value (f->function, NULL, get_current_frame ());
rv->value = get_return_value (func, rv->type);
rv->value_history_index = record_latest_value (rv->value);
}
So seems like that patch would break !RETURN_VALUE_STRUCT_CONVENTION
targets?
I assume that it's record_latest_value that crashes? Isn't the right
fix instead:
rv->value = get_return_value (func, rv->type);
- rv->value_history_index = record_latest_value (rv->value);
+ if (rv->value != NULL)
+ rv->value_history_index = record_latest_value (rv->value);
?
Thanks,
Pedro Alves