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//===------------ BPFCheckAndAdjustIR.cpp - Check and Adjust IR -----------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Check IR and adjust IR for verifier friendly codes.
// The following are done for IR checking:
// - no relocation globals in PHI node.
// The following are done for IR adjustment:
// - remove __builtin_bpf_passthrough builtins. Target independent IR
// optimizations are done and those builtins can be removed.
//
//===----------------------------------------------------------------------===//
#include "BPF.h"
#include "BPFCORE.h"
#include "BPFTargetMachine.h"
#include "llvm/IR/DebugInfoMetadata.h"
#include "llvm/IR/GlobalVariable.h"
#include "llvm/IR/Instruction.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Type.h"
#include "llvm/IR/User.h"
#include "llvm/IR/Value.h"
#include "llvm/Pass.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#define DEBUG_TYPE "bpf-check-and-opt-ir"
using namespace llvm;
namespace {
class BPFCheckAndAdjustIR final : public ModulePass {
bool runOnModule(Module &F) override;
public:
static char ID;
BPFCheckAndAdjustIR() : ModulePass(ID) {}
private:
void checkIR(Module &M);
bool adjustIR(Module &M);
bool removePassThroughBuiltin(Module &M);
bool removeCompareBuiltin(Module &M);
};
} // End anonymous namespace
char BPFCheckAndAdjustIR::ID = 0;
INITIALIZE_PASS(BPFCheckAndAdjustIR, DEBUG_TYPE, "BPF Check And Adjust IR",
false, false)
ModulePass *llvm::createBPFCheckAndAdjustIR() {
return new BPFCheckAndAdjustIR();
}
void BPFCheckAndAdjustIR::checkIR(Module &M) {
// Ensure relocation global won't appear in PHI node
// This may happen if the compiler generated the following code:
// B1:
// g1 = @llvm.skb_buff:0:1...
// ...
// goto B_COMMON
// B2:
// g2 = @llvm.skb_buff:0:2...
// ...
// goto B_COMMON
// B_COMMON:
// g = PHI(g1, g2)
// x = load g
// ...
// If anything likes the above "g = PHI(g1, g2)", issue a fatal error.
for (Function &F : M)
for (auto &BB : F)
for (auto &I : BB) {
PHINode *PN = dyn_cast<PHINode>(&I);
if (!PN || PN->use_empty())
continue;
for (int i = 0, e = PN->getNumIncomingValues(); i < e; ++i) {
auto *GV = dyn_cast<GlobalVariable>(PN->getIncomingValue(i));
if (!GV)
continue;
if (GV->hasAttribute(BPFCoreSharedInfo::AmaAttr) ||
GV->hasAttribute(BPFCoreSharedInfo::TypeIdAttr))
report_fatal_error("relocation global in PHI node");
}
}
}
bool BPFCheckAndAdjustIR::removePassThroughBuiltin(Module &M) {
// Remove __builtin_bpf_passthrough()'s which are used to prevent
// certain IR optimizations. Now major IR optimizations are done,
// remove them.
bool Changed = false;
CallInst *ToBeDeleted = nullptr;
for (Function &F : M)
for (auto &BB : F)
for (auto &I : BB) {
if (ToBeDeleted) {
ToBeDeleted->eraseFromParent();
ToBeDeleted = nullptr;
}
auto *Call = dyn_cast<CallInst>(&I);
if (!Call)
continue;
auto *GV = dyn_cast<GlobalValue>(Call->getCalledOperand());
if (!GV)
continue;
if (!GV->getName().startswith("llvm.bpf.passthrough"))
continue;
Changed = true;
Value *Arg = Call->getArgOperand(1);
Call->replaceAllUsesWith(Arg);
ToBeDeleted = Call;
}
return Changed;
}
bool BPFCheckAndAdjustIR::removeCompareBuiltin(Module &M) {
// Remove __builtin_bpf_compare()'s which are used to prevent
// certain IR optimizations. Now major IR optimizations are done,
// remove them.
bool Changed = false;
CallInst *ToBeDeleted = nullptr;
for (Function &F : M)
for (auto &BB : F)
for (auto &I : BB) {
if (ToBeDeleted) {
ToBeDeleted->eraseFromParent();
ToBeDeleted = nullptr;
}
auto *Call = dyn_cast<CallInst>(&I);
if (!Call)
continue;
auto *GV = dyn_cast<GlobalValue>(Call->getCalledOperand());
if (!GV)
continue;
if (!GV->getName().startswith("llvm.bpf.compare"))
continue;
Changed = true;
Value *Arg0 = Call->getArgOperand(0);
Value *Arg1 = Call->getArgOperand(1);
Value *Arg2 = Call->getArgOperand(2);
auto OpVal = cast<ConstantInt>(Arg0)->getValue().getZExtValue();
CmpInst::Predicate Opcode = (CmpInst::Predicate)OpVal;
auto *ICmp = new ICmpInst(Opcode, Arg1, Arg2);
ICmp->insertBefore(Call);
Call->replaceAllUsesWith(ICmp);
ToBeDeleted = Call;
}
return Changed;
}
bool BPFCheckAndAdjustIR::adjustIR(Module &M) {
bool Changed = removePassThroughBuiltin(M);
Changed = removeCompareBuiltin(M) || Changed;
return Changed;
}
bool BPFCheckAndAdjustIR::runOnModule(Module &M) {
checkIR(M);
return adjustIR(M);
}
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