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

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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

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@278048 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Charles Davis
2016-08-08 21:01:39 +00:00
parent d2aa4c0c88
commit cedd288a90
12 changed files with 168 additions and 22 deletions
Download Patch File Download Diff File Expand all files Collapse all files
lib/CodeGen/PatchableFunction.cpp
+14 -16
View File
@@ -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());
const TargetTransformInfo &TTI =
getAnalysis<TargetTransformInfoWrapperPass>().getTTI(*MF.getFunction());
TTI.emitPatchableOp(PatchType, FirstMBB, FirstActualI);
for (auto &MO : FirstActualI->operands())
MIB.addOperand(MO);
FirstActualI->eraseFromParent();
MF.ensureAlignment(4);
return true;
}