MdePkg/BaseLib: add PatchInstructionX86()

Some edk2 modules generate X86 machine code at module execution time by:

- compiling "template" code with NASM at module build time,

- linking the object code into the module,

- and patching the immediate (constant) operands of some instructions when
  the module is executed.

Add a helper function to BaseLib so that the C code performing the
patching is easier to read and maintain.

The implementation in this patch is taken mainly from Mike Kinney's
mailing list messages at
<http://mid.mail-archive.com/E92EE9817A31E24EB0585FDF735412F5B895C360@ORSMSX113.amr.corp.intel.com>,
<http://mid.mail-archive.com/E92EE9817A31E24EB0585FDF735412F5B898BF66@ORSMSX112.amr.corp.intel.com>.

Cc: Liming Gao <liming.gao@intel.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=866
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>

MdePkg/Library/BaseLib/X86PatchInstruction.c

@@ -0,0 +1,89 @@
+/** @file
+  IA-32/x64 PatchInstructionX86()
+
+  Copyright (C) 2018, Intel Corporation. All rights reserved.<BR>
+  Copyright (C) 2018, Red Hat, Inc.
+
+  This program and the accompanying materials are licensed and made available
+  under the terms and conditions of the BSD License which accompanies this
+  distribution.  The full text of the license may be found at
+  http://opensource.org/licenses/bsd-license.php.
+
+  THE PROGRAM IS DISTRIBUTED UNDER THE BSD LICENSE ON AN "AS IS" BASIS, WITHOUT
+  WARRANTIES OR REPRESENTATIONS OF ANY KIND, EITHER EXPRESS OR IMPLIED.
+**/
+
+#include "BaseLibInternals.h"
+
+/**
+  Patch the immediate operand of an IA32 or X64 instruction such that the byte,
+  word, dword or qword operand is encoded at the end of the instruction's
+  binary representation.
+
+  This function should be used to update object code that was compiled with
+  NASM from assembly source code. Example:
+
+  NASM source code:
+
+        mov     eax, strict dword 0 ; the imm32 zero operand will be patched
+    ASM_PFX(gPatchCr3):
+        mov     cr3, eax
+
+  C source code:
+
+    X86_ASSEMBLY_PATCH_LABEL gPatchCr3;
+    PatchInstructionX86 (gPatchCr3, AsmReadCr3 (), 4);
+
+  @param[out] InstructionEnd  Pointer right past the instruction to patch. The
+                              immediate operand to patch is expected to
+                              comprise the trailing bytes of the instruction.
+                              If InstructionEnd is closer to address 0 than
+                              ValueSize permits, then ASSERT().
+
+  @param[in] PatchValue       The constant to write to the immediate operand.
+                              The caller is responsible for ensuring that
+                              PatchValue can be represented in the byte, word,
+                              dword or qword operand (as indicated through
+                              ValueSize); otherwise ASSERT().
+
+  @param[in] ValueSize        The size of the operand in bytes; must be 1, 2,
+                              4, or 8. ASSERT() otherwise.
+**/
+VOID
+EFIAPI
+PatchInstructionX86 (
+  OUT X86_ASSEMBLY_PATCH_LABEL *InstructionEnd,
+  IN  UINT64                   PatchValue,
+  IN  UINTN                    ValueSize
+  )
+{
+  //
+  // The equality ((UINTN)InstructionEnd == ValueSize) would assume a zero-size
+  // instruction at address 0; forbid it.
+  //
+  ASSERT ((UINTN)InstructionEnd > ValueSize);
+
+  switch (ValueSize) {
+  case 1:
+    ASSERT (PatchValue <= MAX_UINT8);
+    *((UINT8 *)(UINTN)InstructionEnd - 1) = (UINT8)PatchValue;
+    break;
+
+  case 2:
+    ASSERT (PatchValue <= MAX_UINT16);
+    WriteUnaligned16 ((UINT16 *)(UINTN)InstructionEnd - 1, (UINT16)PatchValue);
+    break;
+
+  case 4:
+    ASSERT (PatchValue <= MAX_UINT32);
+    WriteUnaligned32 ((UINT32 *)(UINTN)InstructionEnd - 1, (UINT32)PatchValue);
+    break;
+
+  case 8:
+    WriteUnaligned64 ((UINT64 *)(UINTN)InstructionEnd - 1, PatchValue);
+    break;
+
+  default:
+    ASSERT (FALSE);
+  }
+}