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
|
//===- bolt/Passes/PatchEntries.cpp - Pass for patching function entries --===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// This file implements the PatchEntries class that is used for patching the
// original function entry points. This ensures that only the new/optimized code
// executes and that the old code is never used. This is necessary due to
// current BOLT limitations of not being able to duplicate all function's
// associated metadata (e.g., .eh_frame, exception ranges, debug info,
// jump-tables).
//
// NOTE: A successful run of 'scanExternalRefs' can relax this requirement as
// it also ensures that old code is never executed.
//
//===----------------------------------------------------------------------===//
#include "bolt/Passes/PatchEntries.h"
#include "bolt/Utils/CommandLineOpts.h"
#include "bolt/Utils/NameResolver.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Support/CommandLine.h"
namespace opts {
extern llvm::cl::OptionCategory BoltCategory;
extern llvm::cl::opt<unsigned> Verbosity;
} // namespace opts
namespace llvm {
namespace bolt {
Error PatchEntries::runOnFunctions(BinaryContext &BC) {
if (!opts::ForcePatch) {
// Mark the binary for patching if we did not create external references
// for original code in any of functions we are not going to emit.
bool NeedsPatching = llvm::any_of(
llvm::make_second_range(BC.getBinaryFunctions()),
[&](BinaryFunction &BF) {
return (!BC.shouldEmit(BF) && !BF.hasExternalRefRelocations()) ||
BF.needsPatch();
});
if (!NeedsPatching)
return Error::success();
}
if (opts::Verbosity >= 1)
BC.outs() << "BOLT-INFO: patching entries in original code\n";
// Calculate the size of the patch.
static size_t PatchSize = 0;
if (!PatchSize) {
InstructionListType Seq;
BC.MIB->createLongTailCall(Seq, BC.Ctx->createTempSymbol(), BC.Ctx.get());
PatchSize = BC.computeCodeSize(Seq.begin(), Seq.end());
}
for (auto &BFI : BC.getBinaryFunctions()) {
BinaryFunction &Function = BFI.second;
// Patch original code only for functions that will be emitted.
if (!BC.shouldEmit(Function))
continue;
// Check if we can skip patching the function.
if (!opts::ForcePatch && !Function.hasEHRanges() &&
!Function.needsPatch() && Function.getSize() < PatchThreshold)
continue;
// List of patches for function entries. We either successfully patch
// all entries or, if we cannot patch one or more, do no patch any and
// mark the function as ignorable.
std::vector<Patch> PendingPatches;
uint64_t NextValidByte = 0; // offset of the byte past the last patch
bool Success = Function.forEachEntryPoint([&](uint64_t Offset,
const MCSymbol *Symbol) {
if (Offset < NextValidByte) {
if (opts::Verbosity >= 1)
BC.outs() << "BOLT-INFO: unable to patch entry point in " << Function
<< " at offset 0x" << Twine::utohexstr(Offset) << '\n';
return false;
}
PendingPatches.emplace_back(
Patch{Symbol, Function.getAddress() + Offset});
NextValidByte = Offset + PatchSize;
if (NextValidByte > Function.getMaxSize()) {
if (opts::Verbosity >= 1)
BC.outs() << "BOLT-INFO: function " << Function
<< " too small to patch its entry point\n";
return false;
}
return true;
});
if (!Success) {
// If the original function entries cannot be patched, then we cannot
// safely emit new function body.
BC.errs() << "BOLT-WARNING: failed to patch entries in " << Function
<< ". The function will not be optimized\n";
Function.setIgnored();
continue;
}
for (Patch &Patch : PendingPatches) {
// Add instruction patch to the binary.
InstructionListType Instructions;
BC.MIB->createLongTailCall(Instructions, Patch.Symbol, BC.Ctx.get());
BinaryFunction *PatchFunction = BC.createInstructionPatch(
Patch.Address, Instructions,
NameResolver::append(Patch.Symbol->getName(), ".org.0"));
// Verify the size requirements.
uint64_t HotSize, ColdSize;
std::tie(HotSize, ColdSize) = BC.calculateEmittedSize(*PatchFunction);
assert(!ColdSize && "unexpected cold code");
assert(HotSize <= PatchSize && "max patch size exceeded");
}
}
return Error::success();
}
} // end namespace bolt
} // end namespace llvm
|
