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