[X86] Support the "ms-hotpatch" attribute.

Summary:
Based on two patches by Michael Mueller.

This is a target attribute that causes a function marked with it to be
emitted as "hotpatchable". This particular mechanism was originally
devised by Microsoft for patching their binaries (which they are
constantly updating to stay ahead of crackers, script kiddies, and other
ne'er-do-wells on the Internet), but is now commonly abused by Windows
programs to hook API functions.

This mechanism is target-specific. For x86, a two-byte no-op instruction
is emitted at the function's entry point; the entry point must be
immediately preceded by 64 (32-bit) or 128 (64-bit) bytes of padding.
This padding is where the patch code is written. The two byte no-op is
then overwritten with a short jump into this code. The no-op is usually
a `movl %edi, %edi` instruction; this is used as a magic value
indicating that this is a hotpatchable function.

Reviewers: majnemer, sanjoy, rnk

Subscribers: dberris, llvm-commits

Differential Revision: https://reviews.llvm.org/D19908

llvm-svn: 278048

1 files changed, 14 insertions, 16 deletions

diff --git a/llvm/lib/CodeGen/PatchableFunction.cpp b/llvm/lib/CodeGen/PatchableFunction.cpp
index 32468c90b86..c94307df62b 100644
--- a/llvm/lib/CodeGen/PatchableFunction.cpp
+++ b/llvm/lib/CodeGen/PatchableFunction.cpp
@@ -13,12 +13,11 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/Passes.h"
+#include "llvm/Analysis/TargetTransformInfo.h"
+#include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/MachineFunction.h"
 #include "llvm/CodeGen/MachineFunctionPass.h"
-#include "llvm/CodeGen/MachineInstrBuilder.h"
 #include "llvm/Target/TargetFrameLowering.h"
-#include "llvm/Target/TargetInstrInfo.h"
-#include "llvm/Target/TargetSubtargetInfo.h"
 
 using namespace llvm;
 
@@ -29,8 +28,9 @@ struct PatchableFunction : public MachineFunctionPass {
     initializePatchableFunctionPass(*PassRegistry::getPassRegistry());
   }
 
+  void getAnalysisUsage(AnalysisUsage &AU) const override;
   bool runOnMachineFunction(MachineFunction &F) override;
-   MachineFunctionProperties getRequiredProperties() const override {
+  MachineFunctionProperties getRequiredProperties() const override {
     return MachineFunctionProperties().set(
         MachineFunctionProperties::Property::AllVRegsAllocated);
   }
@@ -53,31 +53,29 @@ static bool doesNotGeneratecode(const MachineInstr &MI) {
   }
 }
 
+void PatchableFunction::getAnalysisUsage(AnalysisUsage &AU) const {
+  MachineFunctionPass::getAnalysisUsage(AU);
+  AU.addRequired<TargetTransformInfoWrapperPass>();
+}
+
 bool PatchableFunction::runOnMachineFunction(MachineFunction &MF) {
   if (!MF.getFunction()->hasFnAttribute("patchable-function"))
     return false;
 
-#ifndef NDEBUG
   Attribute PatchAttr = MF.getFunction()->getFnAttribute("patchable-function");
   StringRef PatchType = PatchAttr.getValueAsString();
-  assert(PatchType == "prologue-short-redirect" && "Only possibility today!");
-#endif
+  assert((PatchType == "prologue-short-redirect" ||
+          PatchType == "ms-hotpatch") && "Only possibilities today!");
 
   auto &FirstMBB = *MF.begin();
   MachineBasicBlock::iterator FirstActualI = FirstMBB.begin();
   for (; doesNotGeneratecode(*FirstActualI); ++FirstActualI)
     assert(FirstActualI != FirstMBB.end());
 
-  auto *TII = MF.getSubtarget().getInstrInfo();
-  auto MIB = BuildMI(FirstMBB, FirstActualI, FirstActualI->getDebugLoc(),
-                     TII->get(TargetOpcode::PATCHABLE_OP))
-                 .addImm(2)
-                 .addImm(FirstActualI->getOpcode());
-
-  for (auto &MO : FirstActualI->operands())
-    MIB.addOperand(MO);
+  const TargetTransformInfo &TTI =
+      getAnalysis<TargetTransformInfoWrapperPass>().getTTI(*MF.getFunction());
+  TTI.emitPatchableOp(PatchType, FirstMBB, FirstActualI);
 
-  FirstActualI->eraseFromParent();
   MF.ensureAlignment(4);
   return true;
 }