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1 : //===- XRayInstrumentation.cpp - Adds XRay instrumentation to functions. --===//
2 : //
3 : // The LLVM Compiler Infrastructure
4 : //
5 : // This file is distributed under the University of Illinois Open Source
6 : // License. See LICENSE.TXT for details.
7 : //
8 : //===----------------------------------------------------------------------===//
9 : //
10 : // This file implements a MachineFunctionPass that inserts the appropriate
11 : // XRay instrumentation instructions. We look for XRay-specific attributes
12 : // on the function to determine whether we should insert the replacement
13 : // operations.
14 : //
15 : //===---------------------------------------------------------------------===//
16 :
17 : #include "llvm/ADT/STLExtras.h"
18 : #include "llvm/ADT/SmallVector.h"
19 : #include "llvm/ADT/Triple.h"
20 : #include "llvm/CodeGen/MachineBasicBlock.h"
21 : #include "llvm/CodeGen/MachineDominators.h"
22 : #include "llvm/CodeGen/MachineFunction.h"
23 : #include "llvm/CodeGen/MachineFunctionPass.h"
24 : #include "llvm/CodeGen/MachineInstrBuilder.h"
25 : #include "llvm/CodeGen/MachineLoopInfo.h"
26 : #include "llvm/CodeGen/TargetInstrInfo.h"
27 : #include "llvm/CodeGen/TargetSubtargetInfo.h"
28 : #include "llvm/IR/Attributes.h"
29 : #include "llvm/IR/Function.h"
30 : #include "llvm/Pass.h"
31 : #include "llvm/Target/TargetMachine.h"
32 :
33 : using namespace llvm;
34 :
35 : namespace {
36 :
37 : struct InstrumentationOptions {
38 : // Whether to emit PATCHABLE_TAIL_CALL.
39 : bool HandleTailcall;
40 :
41 : // Whether to emit PATCHABLE_RET/PATCHABLE_FUNCTION_EXIT for all forms of
42 : // return, e.g. conditional return.
43 : bool HandleAllReturns;
44 : };
45 :
46 : struct XRayInstrumentation : public MachineFunctionPass {
47 : static char ID;
48 :
49 27456 : XRayInstrumentation() : MachineFunctionPass(ID) {
50 27456 : initializeXRayInstrumentationPass(*PassRegistry::getPassRegistry());
51 27456 : }
52 :
53 27269 : void getAnalysisUsage(AnalysisUsage &AU) const override {
54 27269 : AU.setPreservesCFG();
55 : AU.addPreserved<MachineLoopInfo>();
56 : AU.addPreserved<MachineDominatorTree>();
57 27269 : MachineFunctionPass::getAnalysisUsage(AU);
58 27269 : }
59 :
60 : bool runOnMachineFunction(MachineFunction &MF) override;
61 :
62 : private:
63 : // Replace the original RET instruction with the exit sled code ("patchable
64 : // ret" pseudo-instruction), so that at runtime XRay can replace the sled
65 : // with a code jumping to XRay trampoline, which calls the tracing handler
66 : // and, in the end, issues the RET instruction.
67 : // This is the approach to go on CPUs which have a single RET instruction,
68 : // like x86/x86_64.
69 : void replaceRetWithPatchableRet(MachineFunction &MF,
70 : const TargetInstrInfo *TII,
71 : InstrumentationOptions);
72 :
73 : // Prepend the original return instruction with the exit sled code ("patchable
74 : // function exit" pseudo-instruction), preserving the original return
75 : // instruction just after the exit sled code.
76 : // This is the approach to go on CPUs which have multiple options for the
77 : // return instruction, like ARM. For such CPUs we can't just jump into the
78 : // XRay trampoline and issue a single return instruction there. We rather
79 : // have to call the trampoline and return from it to the original return
80 : // instruction of the function being instrumented.
81 : void prependRetWithPatchableExit(MachineFunction &MF,
82 : const TargetInstrInfo *TII,
83 : InstrumentationOptions);
84 : };
85 :
86 : } // end anonymous namespace
87 :
88 0 : void XRayInstrumentation::replaceRetWithPatchableRet(
89 : MachineFunction &MF, const TargetInstrInfo *TII,
90 : InstrumentationOptions op) {
91 : // We look for *all* terminators and returns, then replace those with
92 : // PATCHABLE_RET instructions.
93 : SmallVector<MachineInstr *, 4> Terminators;
94 0 : for (auto &MBB : MF) {
95 0 : for (auto &T : MBB.terminators()) {
96 : unsigned Opc = 0;
97 0 : if (T.isReturn() &&
98 0 : (op.HandleAllReturns || T.getOpcode() == TII->getReturnOpcode())) {
99 : // Replace return instructions with:
100 : // PATCHABLE_RET <Opcode>, <Operand>...
101 : Opc = TargetOpcode::PATCHABLE_RET;
102 : }
103 0 : if (TII->isTailCall(T) && op.HandleTailcall) {
104 : // Treat the tail call as a return instruction, which has a
105 : // different-looking sled than the normal return case.
106 : Opc = TargetOpcode::PATCHABLE_TAIL_CALL;
107 : }
108 0 : if (Opc != 0) {
109 0 : auto MIB = BuildMI(MBB, T, T.getDebugLoc(), TII->get(Opc))
110 0 : .addImm(T.getOpcode());
111 0 : for (auto &MO : T.operands())
112 : MIB.add(MO);
113 0 : Terminators.push_back(&T);
114 : }
115 : }
116 : }
117 :
118 0 : for (auto &I : Terminators)
119 0 : I->eraseFromParent();
120 0 : }
121 :
122 0 : void XRayInstrumentation::prependRetWithPatchableExit(
123 : MachineFunction &MF, const TargetInstrInfo *TII,
124 : InstrumentationOptions op) {
125 0 : for (auto &MBB : MF)
126 0 : for (auto &T : MBB.terminators()) {
127 : unsigned Opc = 0;
128 0 : if (T.isReturn() &&
129 0 : (op.HandleAllReturns || T.getOpcode() == TII->getReturnOpcode())) {
130 : Opc = TargetOpcode::PATCHABLE_FUNCTION_EXIT;
131 : }
132 0 : if (TII->isTailCall(T) && op.HandleTailcall) {
133 : Opc = TargetOpcode::PATCHABLE_TAIL_CALL;
134 : }
135 0 : if (Opc != 0) {
136 : // Prepend the return instruction with PATCHABLE_FUNCTION_EXIT or
137 : // PATCHABLE_TAIL_CALL .
138 0 : BuildMI(MBB, T, T.getDebugLoc(), TII->get(Opc));
139 : }
140 : }
141 0 : }
142 :
143 405986 : bool XRayInstrumentation::runOnMachineFunction(MachineFunction &MF) {
144 405986 : auto &F = MF.getFunction();
145 405986 : auto InstrAttr = F.getFnAttribute("function-instrument");
146 406052 : bool AlwaysInstrument = !InstrAttr.hasAttribute(Attribute::None) &&
147 405986 : InstrAttr.isStringAttribute() &&
148 66 : InstrAttr.getValueAsString() == "xray-always";
149 405986 : Attribute Attr = F.getFnAttribute("xray-instruction-threshold");
150 : unsigned XRayThreshold = 0;
151 405986 : if (!AlwaysInstrument) {
152 405920 : if (Attr.hasAttribute(Attribute::None) || !Attr.isStringAttribute())
153 405915 : return false; // XRay threshold attribute not found.
154 14 : if (Attr.getValueAsString().getAsInteger(10, XRayThreshold))
155 0 : return false; // Invalid value for threshold.
156 :
157 : // Count the number of MachineInstr`s in MachineFunction
158 : int64_t MICount = 0;
159 20 : for (const auto &MBB : MF)
160 13 : MICount += MBB.size();
161 :
162 : // Get MachineDominatorTree or compute it on the fly if it's unavailable
163 7 : auto *MDT = getAnalysisIfAvailable<MachineDominatorTree>();
164 12 : MachineDominatorTree ComputedMDT;
165 7 : if (!MDT) {
166 7 : ComputedMDT.getBase().recalculate(MF);
167 : MDT = &ComputedMDT;
168 : }
169 :
170 : // Get MachineLoopInfo or compute it on the fly if it's unavailable
171 7 : auto *MLI = getAnalysisIfAvailable<MachineLoopInfo>();
172 7 : MachineLoopInfo ComputedMLI;
173 7 : if (!MLI) {
174 7 : ComputedMLI.getBase().analyze(MDT->getBase());
175 : MLI = &ComputedMLI;
176 : }
177 :
178 : // Check if we have a loop.
179 : // FIXME: Maybe make this smarter, and see whether the loops are dependent
180 : // on inputs or side-effects?
181 7 : if (MLI->empty() && MICount < XRayThreshold)
182 : return false; // Function is too small and has no loops.
183 : }
184 :
185 : // We look for the first non-empty MachineBasicBlock, so that we can insert
186 : // the function instrumentation in the appropriate place.
187 : auto MBI = llvm::find_if(
188 0 : MF, [&](const MachineBasicBlock &MBB) { return !MBB.empty(); });
189 71 : if (MBI == MF.end())
190 : return false; // The function is empty.
191 :
192 71 : auto *TII = MF.getSubtarget().getInstrInfo();
193 : auto &FirstMBB = *MBI;
194 : auto &FirstMI = *FirstMBB.begin();
195 :
196 71 : if (!MF.getSubtarget().isXRaySupported()) {
197 0 : FirstMI.emitError("An attempt to perform XRay instrumentation for an"
198 : " unsupported target.");
199 0 : return false;
200 : }
201 :
202 : // First, insert an PATCHABLE_FUNCTION_ENTER as the first instruction of the
203 : // MachineFunction.
204 : BuildMI(FirstMBB, FirstMI, FirstMI.getDebugLoc(),
205 142 : TII->get(TargetOpcode::PATCHABLE_FUNCTION_ENTER));
206 :
207 71 : switch (MF.getTarget().getTargetTriple().getArch()) {
208 35 : case Triple::ArchType::arm:
209 : case Triple::ArchType::thumb:
210 : case Triple::ArchType::aarch64:
211 : case Triple::ArchType::mips:
212 : case Triple::ArchType::mipsel:
213 : case Triple::ArchType::mips64:
214 : case Triple::ArchType::mips64el: {
215 : // For the architectures which don't have a single return instruction
216 : InstrumentationOptions op;
217 35 : op.HandleTailcall = false;
218 35 : op.HandleAllReturns = true;
219 35 : prependRetWithPatchableExit(MF, TII, op);
220 : break;
221 : }
222 8 : case Triple::ArchType::ppc64le: {
223 : // PPC has conditional returns. Turn them into branch and plain returns.
224 : InstrumentationOptions op;
225 8 : op.HandleTailcall = false;
226 8 : op.HandleAllReturns = true;
227 8 : replaceRetWithPatchableRet(MF, TII, op);
228 : break;
229 : }
230 28 : default: {
231 : // For the architectures that have a single return instruction (such as
232 : // RETQ on x86_64).
233 : InstrumentationOptions op;
234 28 : op.HandleTailcall = true;
235 28 : op.HandleAllReturns = false;
236 28 : replaceRetWithPatchableRet(MF, TII, op);
237 : break;
238 : }
239 : }
240 : return true;
241 : }
242 :
243 : char XRayInstrumentation::ID = 0;
244 : char &llvm::XRayInstrumentationID = XRayInstrumentation::ID;
245 31780 : INITIALIZE_PASS_BEGIN(XRayInstrumentation, "xray-instrumentation",
246 : "Insert XRay ops", false, false)
247 31780 : INITIALIZE_PASS_DEPENDENCY(MachineLoopInfo)
248 112603 : INITIALIZE_PASS_END(XRayInstrumentation, "xray-instrumentation",
249 : "Insert XRay ops", false, false)
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