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//===-- ASanStackFrameLayout.cpp - helper for AddressSanitizer ------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
//
// Definition of ComputeASanStackFrameLayout (see ASanStackFrameLayout.h).
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/ASanStackFrameLayout.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/ScopedPrinter.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
namespace llvm {
// We sort the stack variables by alignment (largest first) to minimize
// unnecessary large gaps due to alignment.
// It is tempting to also sort variables by size so that larger variables
// have larger redzones at both ends. But reordering will make report analysis
// harder, especially when temporary unnamed variables are present.
// So, until we can provide more information (type, line number, etc)
// for the stack variables we avoid reordering them too much.
static inline bool CompareVars(const ASanStackVariableDescription &a,
const ASanStackVariableDescription &b) {
return a.Alignment > b.Alignment;
}
// We also force minimal alignment for all vars to kMinAlignment so that vars
// with e.g. alignment 1 and alignment 16 do not get reordered by CompareVars.
static const uint64_t kMinAlignment = 16;
// We want to add a full redzone after every variable.
// The larger the variable Size the larger is the redzone.
// The resulting frame size is a multiple of Alignment.
static uint64_t VarAndRedzoneSize(uint64_t Size, uint64_t Granularity,
uint64_t Alignment) {
uint64_t Res = 0;
if (Size <= 4) Res = 16;
else if (Size <= 16) Res = 32;
else if (Size <= 128) Res = Size + 32;
else if (Size <= 512) Res = Size + 64;
else if (Size <= 4096) Res = Size + 128;
else Res = Size + 256;
return alignTo(std::max(Res, 2 * Granularity), Alignment);
}
ASanStackFrameLayout
ComputeASanStackFrameLayout(SmallVectorImpl<ASanStackVariableDescription> &Vars,
uint64_t Granularity, uint64_t MinHeaderSize) {
assert(Granularity >= 8 && Granularity <= 64 &&
(Granularity & (Granularity - 1)) == 0);
assert(MinHeaderSize >= 16 && (MinHeaderSize & (MinHeaderSize - 1)) == 0 &&
MinHeaderSize >= Granularity);
const size_t NumVars = Vars.size();
assert(NumVars > 0);
for (size_t i = 0; i < NumVars; i++)
Vars[i].Alignment = std::max(Vars[i].Alignment, kMinAlignment);
llvm::stable_sort(Vars, CompareVars);
ASanStackFrameLayout Layout;
Layout.Granularity = Granularity;
Layout.FrameAlignment = std::max(Granularity, Vars[0].Alignment);
uint64_t Offset =
std::max(std::max(MinHeaderSize, Granularity), Vars[0].Alignment);
assert((Offset % Granularity) == 0);
for (size_t i = 0; i < NumVars; i++) {
bool IsLast = i == NumVars - 1;
uint64_t Alignment = std::max(Granularity, Vars[i].Alignment);
(void)Alignment; // Used only in asserts.
uint64_t Size = Vars[i].Size;
assert((Alignment & (Alignment - 1)) == 0);
assert(Layout.FrameAlignment >= Alignment);
assert((Offset % Alignment) == 0);
assert(Size > 0);
uint64_t NextAlignment =
IsLast ? Granularity : std::max(Granularity, Vars[i + 1].Alignment);
uint64_t SizeWithRedzone =
VarAndRedzoneSize(Size, Granularity, NextAlignment);
Vars[i].Offset = Offset;
Offset += SizeWithRedzone;
}
if (Offset % MinHeaderSize) {
Offset += MinHeaderSize - (Offset % MinHeaderSize);
}
Layout.FrameSize = Offset;
assert((Layout.FrameSize % MinHeaderSize) == 0);
return Layout;
}
SmallString<64> ComputeASanStackFrameDescription(
const SmallVectorImpl<ASanStackVariableDescription> &Vars) {
SmallString<2048> StackDescriptionStorage;
raw_svector_ostream StackDescription(StackDescriptionStorage);
StackDescription << Vars.size();
for (const auto &Var : Vars) {
std::string Name = Var.Name;
if (Var.Line) {
Name += ":";
Name += to_string(Var.Line);
}
StackDescription << " " << Var.Offset << " " << Var.Size << " "
<< Name.size() << " " << Name;
}
return StackDescription.str();
}
SmallVector<uint8_t, 64>
GetShadowBytes(const SmallVectorImpl<ASanStackVariableDescription> &Vars,
const ASanStackFrameLayout &Layout) {
assert(Vars.size() > 0);
SmallVector<uint8_t, 64> SB;
SB.clear();
const uint64_t Granularity = Layout.Granularity;
SB.resize(Vars[0].Offset / Granularity, kAsanStackLeftRedzoneMagic);
for (const auto &Var : Vars) {
SB.resize(Var.Offset / Granularity, kAsanStackMidRedzoneMagic);
SB.resize(SB.size() + Var.Size / Granularity, 0);
if (Var.Size % Granularity)
SB.push_back(Var.Size % Granularity);
}
SB.resize(Layout.FrameSize / Granularity, kAsanStackRightRedzoneMagic);
return SB;
}
SmallVector<uint8_t, 64> GetShadowBytesAfterScope(
const SmallVectorImpl<ASanStackVariableDescription> &Vars,
const ASanStackFrameLayout &Layout) {
SmallVector<uint8_t, 64> SB = GetShadowBytes(Vars, Layout);
const uint64_t Granularity = Layout.Granularity;
for (const auto &Var : Vars) {
assert(Var.LifetimeSize <= Var.Size);
const uint64_t LifetimeShadowSize =
(Var.LifetimeSize + Granularity - 1) / Granularity;
const uint64_t Offset = Var.Offset / Granularity;
std::fill(SB.begin() + Offset, SB.begin() + Offset + LifetimeShadowSize,
kAsanStackUseAfterScopeMagic);
}
return SB;
}
} // llvm namespace
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