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

[Laszlo Ersek <lersek@redhat.com>]

On 11/03/16 18:31, 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.
> 
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  MdePkg/Library/BaseMemoryLibOptDxe/ZeroMemWrapper.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/MdePkg/Library/BaseMemoryLibOptDxe/ZeroMemWrapper.c b/MdePkg/Library/BaseMemoryLibOptDxe/ZeroMemWrapper.c
> index 2a0a038fd6c5..fbc2f5742c8c 100644
> --- a/MdePkg/Library/BaseMemoryLibOptDxe/ZeroMemWrapper.c
> +++ b/MdePkg/Library/BaseMemoryLibOptDxe/ZeroMemWrapper.c
> @@ -46,6 +46,10 @@ ZeroMem (
>    IN UINTN  Length
>    )
>  {
> +  if (Length == 0) {
> +    return Buffer;
> +  }
> +
>    ASSERT (!(Buffer == NULL && Length > 0));
>    ASSERT (Length <= (MAX_ADDRESS - (UINTN)Buffer + 1));
>    return InternalMemZeroMem (Buffer, Length);
> 

1. Why is this necessary?

2. After the new check, Length is guaranteed to be positive. The first
ASSERT() should be updated (simplified), I think:

  ASSERT (Buffer != NULL);

Thanks
Laszlo