Re: [PATCH 1/2] MdePkg/BaseMemoryLibOptDxe ARM: fix Thumb-2 bug in ScanMem()

["Gao, Liming" <liming.gao@intel.com>]

Reviewed-by: Liming Gao <liming.gao@intel.com>

> -----Original Message-----
> From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
> Sent: Tuesday, September 27, 2016 6:59 AM
> To: edk2-devel@lists.01.org; Gao, Liming <liming.gao@intel.com>
> Cc: leif.lindholm@linaro.org; Ard Biesheuvel <ard.biesheuvel@linaro.org>
> Subject: [PATCH 1/2] MdePkg/BaseMemoryLibOptDxe ARM: fix Thumb-2
> bug in ScanMem()
> 
> The ARM ScanMem() in BaseMemoryLibOptDxe contains code from the
> open
> source cortex-strings library, and inherited a bug from it where the
> conditional execution of a sequence of instructions is erroneously
> made dependent on the same condition. Since the final 'addeq' is
> supposed to be dependent on the preceding 'tsteq' instruction, they
> cannot be part of the same IT block.
> 
> Contributed-under: TianoCore Contribution Agreement 1.0
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  MdePkg/Library/BaseMemoryLibOptDxe/Arm/ScanMem.S | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/MdePkg/Library/BaseMemoryLibOptDxe/Arm/ScanMem.S
> b/MdePkg/Library/BaseMemoryLibOptDxe/Arm/ScanMem.S
> index dc0e74e8657c..1c269547b072 100644
> --- a/MdePkg/Library/BaseMemoryLibOptDxe/Arm/ScanMem.S
> +++ b/MdePkg/Library/BaseMemoryLibOptDxe/Arm/ScanMem.S
> @@ -134,11 +134,12 @@ ASM_PFX(InternalMemScanMem8):
>      bne     61f
>      adds    r0, r0, #1
>      tst     r5, #CHARTSTMASK(1)     // 2nd character
> -    ittt    eq
> -    addeq   r0, r0 ,#1
> -    tsteq   r5, #(3 << 15)          // 2nd & 3rd character
> +    bne     61f
> +    adds    r0, r0 ,#1
> +    tst     r5, #(3 << 15)          // 2nd & 3rd character
>      // If not the 3rd must be the last one
> -    addeq   r0, r0, #1
> +    it      eq
> +    addeq.n r0, r0, #1
> 
>  61:
>      pop     {r4-r7}
> --
> 2.7.4