1 //===------------ BPFCheckAndAdjustIR.cpp - Check and Adjust IR -----------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // Check IR and adjust IR for verifier friendly codes.
10 // The following are done for IR checking:
11 // - no relocation globals in PHI node.
12 // The following are done for IR adjustment:
13 // - remove __builtin_bpf_passthrough builtins. Target independent IR
14 // optimizations are done and those builtins can be removed.
15 //
16 //===----------------------------------------------------------------------===//
17
18 #include "BPF.h"
19 #include "BPFCORE.h"
20 #include "BPFTargetMachine.h"
21 #include "llvm/IR/DebugInfoMetadata.h"
22 #include "llvm/IR/GlobalVariable.h"
23 #include "llvm/IR/Instruction.h"
24 #include "llvm/IR/Instructions.h"
25 #include "llvm/IR/Module.h"
26 #include "llvm/IR/Type.h"
27 #include "llvm/IR/User.h"
28 #include "llvm/IR/Value.h"
29 #include "llvm/Pass.h"
30 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
31
32 #define DEBUG_TYPE "bpf-check-and-opt-ir"
33
34 using namespace llvm;
35
36 namespace {
37
38 class BPFCheckAndAdjustIR final : public ModulePass {
39 bool runOnModule(Module &F) override;
40
41 public:
42 static char ID;
BPFCheckAndAdjustIR()43 BPFCheckAndAdjustIR() : ModulePass(ID) {}
44
45 private:
46 void checkIR(Module &M);
47 bool adjustIR(Module &M);
48 bool removePassThroughBuiltin(Module &M);
49 };
50 } // End anonymous namespace
51
52 char BPFCheckAndAdjustIR::ID = 0;
53 INITIALIZE_PASS(BPFCheckAndAdjustIR, DEBUG_TYPE, "BPF Check And Adjust IR",
54 false, false)
55
createBPFCheckAndAdjustIR()56 ModulePass *llvm::createBPFCheckAndAdjustIR() {
57 return new BPFCheckAndAdjustIR();
58 }
59
checkIR(Module & M)60 void BPFCheckAndAdjustIR::checkIR(Module &M) {
61 // Ensure relocation global won't appear in PHI node
62 // This may happen if the compiler generated the following code:
63 // B1:
64 // g1 = @llvm.skb_buff:0:1...
65 // ...
66 // goto B_COMMON
67 // B2:
68 // g2 = @llvm.skb_buff:0:2...
69 // ...
70 // goto B_COMMON
71 // B_COMMON:
72 // g = PHI(g1, g2)
73 // x = load g
74 // ...
75 // If anything likes the above "g = PHI(g1, g2)", issue a fatal error.
76 for (Function &F : M)
77 for (auto &BB : F)
78 for (auto &I : BB) {
79 PHINode *PN = dyn_cast<PHINode>(&I);
80 if (!PN || PN->use_empty())
81 continue;
82 for (int i = 0, e = PN->getNumIncomingValues(); i < e; ++i) {
83 auto *GV = dyn_cast<GlobalVariable>(PN->getIncomingValue(i));
84 if (!GV)
85 continue;
86 if (GV->hasAttribute(BPFCoreSharedInfo::AmaAttr) ||
87 GV->hasAttribute(BPFCoreSharedInfo::TypeIdAttr))
88 report_fatal_error("relocation global in PHI node");
89 }
90 }
91 }
92
removePassThroughBuiltin(Module & M)93 bool BPFCheckAndAdjustIR::removePassThroughBuiltin(Module &M) {
94 // Remove __builtin_bpf_passthrough()'s which are used to prevent
95 // certain IR optimizations. Now major IR optimizations are done,
96 // remove them.
97 bool Changed = false;
98 CallInst *ToBeDeleted = nullptr;
99 for (Function &F : M)
100 for (auto &BB : F)
101 for (auto &I : BB) {
102 if (ToBeDeleted) {
103 ToBeDeleted->eraseFromParent();
104 ToBeDeleted = nullptr;
105 }
106
107 auto *Call = dyn_cast<CallInst>(&I);
108 if (!Call)
109 continue;
110 auto *GV = dyn_cast<GlobalValue>(Call->getCalledOperand());
111 if (!GV)
112 continue;
113 if (!GV->getName().startswith("llvm.bpf.passthrough"))
114 continue;
115 Changed = true;
116 Value *Arg = Call->getArgOperand(1);
117 Call->replaceAllUsesWith(Arg);
118 ToBeDeleted = Call;
119 }
120 return Changed;
121 }
122
adjustIR(Module & M)123 bool BPFCheckAndAdjustIR::adjustIR(Module &M) {
124 return removePassThroughBuiltin(M);
125 }
126
runOnModule(Module & M)127 bool BPFCheckAndAdjustIR::runOnModule(Module &M) {
128 checkIR(M);
129 return adjustIR(M);
130 }
131