X-Git-Url: https://git.proxmox.com/?p=mirror_edk2.git;a=blobdiff_plain;f=MdePkg%2FInclude%2FLibrary%2FBaseLib.h;h=eb2899f8524e7a8e1856d68f0c25ced58c4253fb;hp=e4455e71d5c3fab916ec14ab760204355b9c1c86;hb=8596c140907ebfeabf62427686280666a4e04893;hpb=de4f7f52f2003b854a754e3815f0a0c1c611118f

diff --git a/MdePkg/Include/Library/BaseLib.h b/MdePkg/Include/Library/BaseLib.h
index e4455e71d5..eb2899f852 100644
--- a/MdePkg/Include/Library/BaseLib.h
+++ b/MdePkg/Include/Library/BaseLib.h
@@ -6881,6 +6881,20 @@ typedef struct {
 #define THUNK_ATTRIBUTE_DISABLE_A20_MASK_INT_15   0x00000002
 #define THUNK_ATTRIBUTE_DISABLE_A20_MASK_KBD_CTRL 0x00000004
 
+///
+/// Type definition for representing labels in NASM source code that allow for
+/// the patching of immediate operands of IA32 and X64 instructions.
+///
+/// While the type is technically defined as a function type (note: not a
+/// pointer-to-function type), such labels in NASM source code never stand for
+/// actual functions, and identifiers declared with this function type should
+/// never be called. This is also why the EFIAPI calling convention specifier
+/// is missing from the typedef, and why the typedef does not follow the usual
+/// edk2 coding style for function (or pointer-to-function) typedefs. The VOID
+/// return type and the VOID argument list are merely artifacts.
+///
+typedef VOID (X86_ASSEMBLY_PATCH_LABEL) (VOID);
+
 /**
   Retrieves CPUID information.
 
@@ -9068,5 +9082,47 @@ AsmWriteTr (
   IN UINT16 Selector
   );
 
+/**
+  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
+  );
+
 #endif // defined (MDE_CPU_IA32) || defined (MDE_CPU_X64)
 #endif // !defined (__BASE_LIB__)