UefiCpuPkg/PiSmmCpuDxeSmm: Fix ASSERT for success.

Index is initialized to MAX_UINT16 as default failure value, which
is what the ASSERT is supposed to test for.  The ASSERT condition
however can never return FALSE for INT16 != int, as due to
Integer Promotion[1], Index is converted to int, which can never
result in -1.

Furthermore, Index is used as a for loop index variable inbetween its
initialization and the ASSERT, so the value is unconditionally
overwritten too.

Fix the ASSERT check to compare Index to its upper boundary, which it
will be equal to if the loop was not broken out of on success.

[1] ISO/IEC 9899:2011, 6.5.9.4

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Marvin Haeuser <Marvin.Haeuser@outlook.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>

diff --git a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c
index b7c3ad31e82cc654fc9fe348624f8f07594d11fd..89b3f2b7257f3a057d9e9f8257da25ce15db7440 100644 (file)
--- a/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c
+++ b/UefiCpuPkg/PiSmmCpuDxeSmm/X64/SmmFuncsArch.c
@@ -110,7 +110,6 @@ GetProtectedModeCS (
   UINTN                    GdtEntryCount;\r
   UINT16                   Index;\r
 \r
   UINTN                    GdtEntryCount;\r
   UINT16                   Index;\r
 \r

-  Index = (UINT16) -1;\r

   AsmReadGdtr (&GdtrDesc);\r
   GdtEntryCount = (GdtrDesc.Limit + 1) / sizeof (IA32_SEGMENT_DESCRIPTOR);\r
   GdtEntry = (IA32_SEGMENT_DESCRIPTOR *) GdtrDesc.Base;\r
   AsmReadGdtr (&GdtrDesc);\r
   GdtEntryCount = (GdtrDesc.Limit + 1) / sizeof (IA32_SEGMENT_DESCRIPTOR);\r
   GdtEntry = (IA32_SEGMENT_DESCRIPTOR *) GdtrDesc.Base;\r


@@ -122,7 +121,7 @@ GetProtectedModeCS (
     }\r
     GdtEntry++;\r
   }\r
     }\r
     GdtEntry++;\r
   }\r

-  ASSERT (Index != -1);\r
+  ASSERT (Index != GdtEntryCount);\r

   return Index * 8;\r
 }\r
 \r
   return Index * 8;\r
 }\r
 \r