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//===- JMCInstrumenter.cpp - JMC Instrumentation --------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// JMCInstrumenter pass:
// - instrument each function with a call to __CheckForDebuggerJustMyCode. The
// sole argument should be defined in .msvcjmc. Each flag is 1 byte initilized
// to 1.
// - create the dummy COMDAT function __JustMyCode_Default to prevent linking
// error if __CheckForDebuggerJustMyCode is not available.
// - For MSVC:
// add "/alternatename:__CheckForDebuggerJustMyCode=__JustMyCode_Default" to
// "llvm.linker.options"
// For ELF:
// Rename __JustMyCode_Default to __CheckForDebuggerJustMyCode and mark it as
// weak symbol.
//===----------------------------------------------------------------------===//
#include "llvm/CodeGen/JMCInstrumenter.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/CodeGen/Passes.h"
#include "llvm/IR/DIBuilder.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/InitializePasses.h"
#include "llvm/Pass.h"
#include "llvm/Support/DJB.h"
#include "llvm/Support/Path.h"
#include "llvm/Transforms/Utils/ModuleUtils.h"
using namespace llvm;
#define DEBUG_TYPE "jmc-instrumenter"
static bool runImpl(Module &M);
namespace {
struct JMCInstrumenter : public ModulePass {
static char ID;
JMCInstrumenter() : ModulePass(ID) {
initializeJMCInstrumenterPass(*PassRegistry::getPassRegistry());
}
bool runOnModule(Module &M) override { return runImpl(M); }
};
char JMCInstrumenter::ID = 0;
} // namespace
PreservedAnalyses JMCInstrumenterPass::run(Module &M, ModuleAnalysisManager &) {
bool Changed = runImpl(M);
return Changed ? PreservedAnalyses::none() : PreservedAnalyses::all();
}
INITIALIZE_PASS(
JMCInstrumenter, DEBUG_TYPE,
"Instrument function entry with call to __CheckForDebuggerJustMyCode",
false, false)
ModulePass *llvm::createJMCInstrumenterPass() { return new JMCInstrumenter(); }
namespace {
const char CheckFunctionName[] = "__CheckForDebuggerJustMyCode";
std::string getFlagName(DISubprogram &SP, bool UseX86FastCall) {
// absolute windows path: windows_backslash
// relative windows backslash path: windows_backslash
// relative windows slash path: posix
// absolute posix path: posix
// relative posix path: posix
sys::path::Style PathStyle =
has_root_name(SP.getDirectory(), sys::path::Style::windows_backslash) ||
SP.getDirectory().contains("\\") ||
SP.getFilename().contains("\\")
? sys::path::Style::windows_backslash
: sys::path::Style::posix;
// Best effort path normalization. This is to guarantee an unique flag symbol
// is produced for the same directory. Some builds may want to use relative
// paths, or paths with a specific prefix (see the -fdebug-compilation-dir
// flag), so only hash paths in debuginfo. Don't expand them to absolute
// paths.
SmallString<256> FilePath(SP.getDirectory());
sys::path::append(FilePath, PathStyle, SP.getFilename());
sys::path::native(FilePath, PathStyle);
sys::path::remove_dots(FilePath, /*remove_dot_dot=*/true, PathStyle);
// The naming convention for the flag name is __<hash>_<file name> with '.' in
// <file name> replaced with '@'. For example C:\file.any.c would have a flag
// __D032E919_file@any@c. The naming convention match MSVC's format however
// the match is not required to make JMC work. The hashing function used here
// is different from MSVC's.
std::string Suffix;
for (auto C : sys::path::filename(FilePath, PathStyle))
Suffix.push_back(C == '.' ? '@' : C);
sys::path::remove_filename(FilePath, PathStyle);
return (UseX86FastCall ? "_" : "__") +
utohexstr(djbHash(FilePath), /*LowerCase=*/false,
/*Width=*/8) +
"_" + Suffix;
}
void attachDebugInfo(GlobalVariable &GV, DISubprogram &SP) {
Module &M = *GV.getParent();
DICompileUnit *CU = SP.getUnit();
assert(CU);
DIBuilder DB(M, false, CU);
auto *DType =
DB.createBasicType("unsigned char", 8, dwarf::DW_ATE_unsigned_char,
llvm::DINode::FlagArtificial);
auto *DGVE = DB.createGlobalVariableExpression(
CU, GV.getName(), /*LinkageName=*/StringRef(), SP.getFile(),
/*LineNo=*/0, DType, /*IsLocalToUnit=*/true, /*IsDefined=*/true);
GV.addMetadata(LLVMContext::MD_dbg, *DGVE);
DB.finalize();
}
FunctionType *getCheckFunctionType(LLVMContext &Ctx) {
Type *VoidTy = Type::getVoidTy(Ctx);
PointerType *VoidPtrTy = PointerType::getUnqual(Ctx);
return FunctionType::get(VoidTy, VoidPtrTy, false);
}
Function *createDefaultCheckFunction(Module &M, bool UseX86FastCall) {
LLVMContext &Ctx = M.getContext();
const char *DefaultCheckFunctionName =
UseX86FastCall ? "_JustMyCode_Default" : "__JustMyCode_Default";
// Create the function.
Function *DefaultCheckFunc =
Function::Create(getCheckFunctionType(Ctx), GlobalValue::ExternalLinkage,
DefaultCheckFunctionName, &M);
DefaultCheckFunc->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
DefaultCheckFunc->addParamAttr(0, Attribute::NoUndef);
if (UseX86FastCall)
DefaultCheckFunc->addParamAttr(0, Attribute::InReg);
BasicBlock *EntryBB = BasicBlock::Create(Ctx, "", DefaultCheckFunc);
ReturnInst::Create(Ctx, EntryBB);
return DefaultCheckFunc;
}
} // namespace
bool runImpl(Module &M) {
bool Changed = false;
LLVMContext &Ctx = M.getContext();
Triple ModuleTriple(M.getTargetTriple());
bool IsMSVC = ModuleTriple.isKnownWindowsMSVCEnvironment();
bool IsELF = ModuleTriple.isOSBinFormatELF();
assert((IsELF || IsMSVC) && "Unsupported triple for JMC");
bool UseX86FastCall = IsMSVC && ModuleTriple.getArch() == Triple::x86;
const char *const FlagSymbolSection = IsELF ? ".data.just.my.code" : ".msvcjmc";
GlobalValue *CheckFunction = nullptr;
DenseMap<DISubprogram *, Constant *> SavedFlags(8);
for (auto &F : M) {
if (F.isDeclaration())
continue;
auto *SP = F.getSubprogram();
if (!SP)
continue;
Constant *&Flag = SavedFlags[SP];
if (!Flag) {
std::string FlagName = getFlagName(*SP, UseX86FastCall);
IntegerType *FlagTy = Type::getInt8Ty(Ctx);
Flag = M.getOrInsertGlobal(FlagName, FlagTy, [&] {
// FIXME: Put the GV in comdat and have linkonce_odr linkage to save
// .msvcjmc section space? maybe not worth it.
GlobalVariable *GV = new GlobalVariable(
M, FlagTy, /*isConstant=*/false, GlobalValue::InternalLinkage,
ConstantInt::get(FlagTy, 1), FlagName);
GV->setSection(FlagSymbolSection);
GV->setAlignment(Align(1));
GV->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
attachDebugInfo(*GV, *SP);
return GV;
});
}
if (!CheckFunction) {
Function *DefaultCheckFunc =
createDefaultCheckFunction(M, UseX86FastCall);
if (IsELF) {
DefaultCheckFunc->setName(CheckFunctionName);
DefaultCheckFunc->setLinkage(GlobalValue::WeakAnyLinkage);
CheckFunction = DefaultCheckFunc;
} else {
assert(!M.getFunction(CheckFunctionName) &&
"JMC instrument more than once?");
auto *CheckFunc = cast<Function>(
M.getOrInsertFunction(CheckFunctionName, getCheckFunctionType(Ctx))
.getCallee());
CheckFunc->setUnnamedAddr(GlobalValue::UnnamedAddr::Global);
CheckFunc->addParamAttr(0, Attribute::NoUndef);
if (UseX86FastCall) {
CheckFunc->setCallingConv(CallingConv::X86_FastCall);
CheckFunc->addParamAttr(0, Attribute::InReg);
}
CheckFunction = CheckFunc;
StringRef DefaultCheckFunctionName = DefaultCheckFunc->getName();
appendToUsed(M, {DefaultCheckFunc});
Comdat *C = M.getOrInsertComdat(DefaultCheckFunctionName);
C->setSelectionKind(Comdat::Any);
DefaultCheckFunc->setComdat(C);
// Add a linker option /alternatename to set the default implementation
// for the check function.
// https://devblogs.microsoft.com/oldnewthing/20200731-00/?p=104024
std::string AltOption = std::string("/alternatename:") +
CheckFunctionName + "=" +
DefaultCheckFunctionName.str();
llvm::Metadata *Ops[] = {llvm::MDString::get(Ctx, AltOption)};
MDTuple *N = MDNode::get(Ctx, Ops);
M.getOrInsertNamedMetadata("llvm.linker.options")->addOperand(N);
}
}
// FIXME: it would be nice to make CI scheduling boundary, although in
// practice it does not matter much.
auto *CI = CallInst::Create(getCheckFunctionType(Ctx), CheckFunction,
{Flag}, "", F.begin()->getFirstInsertionPt());
CI->addParamAttr(0, Attribute::NoUndef);
if (UseX86FastCall) {
CI->setCallingConv(CallingConv::X86_FastCall);
CI->addParamAttr(0, Attribute::InReg);
}
Changed = true;
}
return Changed;
}
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