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//===-- ASanStackFrameLayout.cpp - helper for AddressSanitizer ------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// Definition of ComputeASanStackFrameLayout (see ASanStackFrameLayout.h).
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/ASanStackFrameLayout.h"
#include "llvm/ADT/SmallString.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 size_t kMinAlignment = 16;
static size_t RoundUpTo(size_t X, size_t RoundTo) {
assert((RoundTo & (RoundTo - 1)) == 0);
return (X + RoundTo - 1) & ~(RoundTo - 1);
}
// The larger the variable Size the larger is the redzone.
// The resulting frame size is a multiple of Alignment.
static size_t VarAndRedzoneSize(size_t Size, size_t Alignment) {
size_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 RoundUpTo(Res, Alignment);
}
void
ComputeASanStackFrameLayout(SmallVectorImpl<ASanStackVariableDescription> &Vars,
size_t Granularity, size_t MinHeaderSize,
ASanStackFrameLayout *Layout) {
assert(Granularity >= 8 && Granularity <= 64 &&
(Granularity & (Granularity - 1)) == 0);
assert(MinHeaderSize >= 16 && (MinHeaderSize & (MinHeaderSize - 1)) == 0 &&
MinHeaderSize >= Granularity);
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);
std::stable_sort(Vars.begin(), Vars.end(), CompareVars);
SmallString<2048> StackDescriptionStorage;
raw_svector_ostream StackDescription(StackDescriptionStorage);
StackDescription << NumVars;
Layout->FrameAlignment = std::max(Granularity, Vars[0].Alignment);
SmallVector<uint8_t, 64> &SB(Layout->ShadowBytes);
SB.clear();
size_t Offset = std::max(std::max(MinHeaderSize, Granularity),
Vars[0].Alignment);
assert((Offset % Granularity) == 0);
SB.insert(SB.end(), Offset / Granularity, kAsanStackLeftRedzoneMagic);
for (size_t i = 0; i < NumVars; i++) {
bool IsLast = i == NumVars - 1;
size_t Alignment = std::max(Granularity, Vars[i].Alignment);
(void)Alignment; // Used only in asserts.
size_t Size = Vars[i].Size;
const char *Name = Vars[i].Name;
assert((Alignment & (Alignment - 1)) == 0);
assert(Layout->FrameAlignment >= Alignment);
assert((Offset % Alignment) == 0);
assert(Size > 0);
StackDescription << " " << Offset << " " << Size << " " << strlen(Name)
<< " " << Name;
size_t NextAlignment = IsLast ? Granularity
: std::max(Granularity, Vars[i + 1].Alignment);
size_t SizeWithRedzone = VarAndRedzoneSize(Vars[i].Size, NextAlignment);
SB.insert(SB.end(), Size / Granularity, 0);
if (Size % Granularity)
SB.insert(SB.end(), Size % Granularity);
SB.insert(SB.end(), (SizeWithRedzone - Size) / Granularity,
IsLast ? kAsanStackRightRedzoneMagic
: kAsanStackMidRedzoneMagic);
Vars[i].Offset = Offset;
Offset += SizeWithRedzone;
}
if (Offset % MinHeaderSize) {
size_t ExtraRedzone = MinHeaderSize - (Offset % MinHeaderSize);
SB.insert(SB.end(), ExtraRedzone / Granularity,
kAsanStackRightRedzoneMagic);
Offset += ExtraRedzone;
}
Layout->DescriptionString = StackDescription.str();
Layout->FrameSize = Offset;
assert((Layout->FrameSize % MinHeaderSize) == 0);
assert(Layout->FrameSize / Granularity == Layout->ShadowBytes.size());
}
} // llvm namespace
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