Re: [PATCH] Fix off-by-one in call to vector::reserve

[John Baldwin <jhb@FreeBSD.org>]

On 8/18/23 7:03 AM, Tom Tromey via Gdb-patches wrote:
> While looking at a bug, I noticed what I think is an off-by-one
> mistake in a call to vector::reserve.  This code:
> 
>        new_args.reserve (args.size ());
>        new_args.push_back
> 	(value_from_pointer (lookup_pointer_type (values_type), struct_addr));
>        new_args.insert (new_args.end (), args.begin (), args.end ());
> 
> ... reserves 'size()' entries, but then proceeds to push one extra
> one.
> 
> This shouldn't have any really bad effects, as insert will grow the
> vector.  Still, it seems better to use the correct size if we're going
> to bother calling reserve.
> 
> Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30780
> ---
>   gdb/infcall.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/gdb/infcall.c b/gdb/infcall.c
> index bea5b185ddc..7e19be79a24 100644
> --- a/gdb/infcall.c
> +++ b/gdb/infcall.c
> @@ -1233,7 +1233,7 @@ call_function_by_hand_dummy (struct value *function,
>     if (return_method == return_method_hidden_param)
>       {
>         /* Add the new argument to the front of the argument list.  */
> -      new_args.reserve (args.size ());
> +      new_args.reserve (args.size () + 1);
>         new_args.push_back
>   	(value_from_pointer (lookup_pointer_type (values_type), struct_addr));
>         new_args.insert (new_args.end (), args.begin (), args.end ());

Pedantically speaking I would probably write it as '1 + args.size()' as the
extra pointer is pushed first followed by a copy of all the items in args
(that is, trying to make the expression list the sub-sizes in the same order
they are added to the vector).

Reviewed-by: John Baldwin <jhb@FreeBSD.org>

-- 
John Baldwin