Re: [PATCH-for-5.0] gdbstub: Do not use memset() on GByteArray

[Peter Maydell <peter.maydell@linaro.org>]

On Tue, 14 Apr 2020 at 11:24, Philippe Mathieu-Daudé <philmd@redhat.com> wrote:
>
> Introduce gdb_get_zeroes() to fill a GByteArray with zeroes.
>
> Fixes: a010bdbe719 ("extend GByteArray to read register helpers")
> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
> ---
>  include/exec/gdbstub.h  | 9 +++++++++
>  target/arm/gdbstub.c    | 3 +--
>  target/xtensa/gdbstub.c | 6 ++----
>  3 files changed, 12 insertions(+), 6 deletions(-)
>
> diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
> index 30b909ebd2..b52d9933ee 100644
> --- a/include/exec/gdbstub.h
> +++ b/include/exec/gdbstub.h
> @@ -125,6 +125,15 @@ static inline int gdb_get_reg128(GByteArray *buf, uint64_t val_hi,
>      return 16;
>  }
>
> +static inline int gdb_get_zeroes(GByteArray *array, size_t len)
> +{
> +    for (size_t i = 0; i < len; i++) {
> +        gdb_get_reg8(array, '\0');
> +    }
> +
> +    return len;
> +}

The other implementation option here would be

     guint oldlen = array->len;
     g_byte_array_set_size(array, oldlen + len);
     memset(array->data + oldlen, 0, len);

For length values < 16 my guess is the perf difference is
not going to be noticeable though.

thanks
-- PMM