Re: [PATCH v2] MdePkg/BaseMemoryLibOptDxe: check for zero length in ZeroMem ()

[Laszlo Ersek <lersek@redhat.com>]

On 11/03/16 19:18, Ard Biesheuvel wrote:
> Unlike other string functions in this library, ZeroMem () does not
> return early when the length of the input buffer is 0. So add the
> same to ZeroMem () as well.
> 
> This fixes an issue with the ARM implementation, whose InternalMemZeroMem
> code does not expect a length of 0, and always writes at least a single
> byte.
> 
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  MdePkg/Library/BaseMemoryLibOptDxe/ZeroMemWrapper.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/MdePkg/Library/BaseMemoryLibOptDxe/ZeroMemWrapper.c b/MdePkg/Library/BaseMemoryLibOptDxe/ZeroMemWrapper.c
> index 2a0a038fd6c5..9dd0b45e188e 100644
> --- a/MdePkg/Library/BaseMemoryLibOptDxe/ZeroMemWrapper.c
> +++ b/MdePkg/Library/BaseMemoryLibOptDxe/ZeroMemWrapper.c
> @@ -46,7 +46,11 @@ ZeroMem (
>    IN UINTN  Length
>    )
>  {
> -  ASSERT (!(Buffer == NULL && Length > 0));
> +  if (Length == 0) {
> +    return Buffer;
> +  }
> +
> +  ASSERT (Buffer != NULL);
>    ASSERT (Length <= (MAX_ADDRESS - (UINTN)Buffer + 1));
>    return InternalMemZeroMem (Buffer, Length);
>  }
> 

Assuming the ARM impl of InternalMemZeroMem() conforms to the
InternalMemZeroMem() contract -- if there is such a contract --, I think
this patch makes sense:

Acked-by: Laszlo Ersek <lersek@redhat.com>

Thanks
Laszlo