[PATCH 1/2] MdePkg/BasePrintLib: Fix incomplete print output

[Jian J Wang <jian.j.wang@intel.com>]

This is caused by previous patch which tried to fix string over-read,
which breaks UEFI menu rendering: the following

/------------------------------------------------------------------------------\
|                               Device Manager                                 |
\------------------------------------------------------------------------------/

is rendered as

/\
|                               Device Manager                                 |
\/.0                                                 2.00 GHz

(the spurious digits are SMBIOS data from the home screen)

The problem appears to be that the CHAR16 value of BOXDRAW_HORIZONTAL
equals 0x2500, which means that testing ArgumentString[] != '\0'
(which tests the low byte only) will yield FALSE and terminate the
loop prematurely.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
 MdePkg/Library/BasePrintLib/PrintLibInternal.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/MdePkg/Library/BasePrintLib/PrintLibInternal.c b/MdePkg/Library/BasePrintLib/PrintLibInternal.c
index fc57255068..6f19b31449 100644
--- a/MdePkg/Library/BasePrintLib/PrintLibInternal.c
+++ b/MdePkg/Library/BasePrintLib/PrintLibInternal.c
@@ -1108,7 +1108,9 @@ BasePrintLibSPrintMarker (
       // ArgumentString is either null-terminated, or it contains Precision characters
       //
       for (Count = 0;
-            ArgumentString[Count * BytesPerArgumentCharacter] != '\0' &&
+            (ArgumentString[Count * BytesPerArgumentCharacter] != '\0' ||
+             (BytesPerArgumentCharacter > 1 &&
+              ArgumentString[Count * BytesPerArgumentCharacter + 1]!= '\0')) &&
             (Count < Precision || ((Flags & PRECISION) == 0));
               Count++) {
         ArgumentCharacter = ((ArgumentString[Count * BytesPerArgumentCharacter] & 0xff) | ((ArgumentString[Count * BytesPerArgumentCharacter + 1]) << 8)) & ArgumentMask;
@@ -1167,7 +1169,9 @@ BasePrintLibSPrintMarker (
     //
     // Copy the string into the output buffer performing the required type conversions
     //
-    while (Index < Count && (*ArgumentString) != '\0') {
+    while (Index < Count &&
+           (ArgumentString[0] != '\0' ||
+            (BytesPerArgumentCharacter > 1 && ArgumentString[1] != '\0'))) {
       ArgumentCharacter = ((*ArgumentString & 0xff) | (((UINT8)*(ArgumentString + 1)) << 8)) & ArgumentMask;
 
       LengthToReturn += (1 * BytesPerOutputCharacter);
-- 
2.15.1.windows.2