llvm/lib/CodeGen/SafeStackLayout.cpp
Chandler Carruth 6b547686c5 Update the file headers across all of the LLVM projects in the monorepo
to reflect the new license.

We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.

Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351636 91177308-0d34-0410-b5e6-96231b3b80d8
2019-01-19 08:50:56 +00:00

154 lines
5.3 KiB
C++

//===- SafeStackLayout.cpp - SafeStack frame layout -----------------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
#include "SafeStackLayout.h"
#include "SafeStackColoring.h"
#include "llvm/IR/Value.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <cassert>
using namespace llvm;
using namespace llvm::safestack;
#define DEBUG_TYPE "safestacklayout"
static cl::opt<bool> ClLayout("safe-stack-layout",
cl::desc("enable safe stack layout"), cl::Hidden,
cl::init(true));
LLVM_DUMP_METHOD void StackLayout::print(raw_ostream &OS) {
OS << "Stack regions:\n";
for (unsigned i = 0; i < Regions.size(); ++i) {
OS << " " << i << ": [" << Regions[i].Start << ", " << Regions[i].End
<< "), range " << Regions[i].Range << "\n";
}
OS << "Stack objects:\n";
for (auto &IT : ObjectOffsets) {
OS << " at " << IT.getSecond() << ": " << *IT.getFirst() << "\n";
}
}
void StackLayout::addObject(const Value *V, unsigned Size, unsigned Alignment,
const StackColoring::LiveRange &Range) {
StackObjects.push_back({V, Size, Alignment, Range});
ObjectAlignments[V] = Alignment;
MaxAlignment = std::max(MaxAlignment, Alignment);
}
static unsigned AdjustStackOffset(unsigned Offset, unsigned Size,
unsigned Alignment) {
return alignTo(Offset + Size, Alignment) - Size;
}
void StackLayout::layoutObject(StackObject &Obj) {
if (!ClLayout) {
// If layout is disabled, just grab the next aligned address.
// This effectively disables stack coloring as well.
unsigned LastRegionEnd = Regions.empty() ? 0 : Regions.back().End;
unsigned Start = AdjustStackOffset(LastRegionEnd, Obj.Size, Obj.Alignment);
unsigned End = Start + Obj.Size;
Regions.emplace_back(Start, End, Obj.Range);
ObjectOffsets[Obj.Handle] = End;
return;
}
LLVM_DEBUG(dbgs() << "Layout: size " << Obj.Size << ", align "
<< Obj.Alignment << ", range " << Obj.Range << "\n");
assert(Obj.Alignment <= MaxAlignment);
unsigned Start = AdjustStackOffset(0, Obj.Size, Obj.Alignment);
unsigned End = Start + Obj.Size;
LLVM_DEBUG(dbgs() << " First candidate: " << Start << " .. " << End << "\n");
for (const StackRegion &R : Regions) {
LLVM_DEBUG(dbgs() << " Examining region: " << R.Start << " .. " << R.End
<< ", range " << R.Range << "\n");
assert(End >= R.Start);
if (Start >= R.End) {
LLVM_DEBUG(dbgs() << " Does not intersect, skip.\n");
continue;
}
if (Obj.Range.Overlaps(R.Range)) {
// Find the next appropriate location.
Start = AdjustStackOffset(R.End, Obj.Size, Obj.Alignment);
End = Start + Obj.Size;
LLVM_DEBUG(dbgs() << " Overlaps. Next candidate: " << Start << " .. "
<< End << "\n");
continue;
}
if (End <= R.End) {
LLVM_DEBUG(dbgs() << " Reusing region(s).\n");
break;
}
}
unsigned LastRegionEnd = Regions.empty() ? 0 : Regions.back().End;
if (End > LastRegionEnd) {
// Insert a new region at the end. Maybe two.
if (Start > LastRegionEnd) {
LLVM_DEBUG(dbgs() << " Creating gap region: " << LastRegionEnd << " .. "
<< Start << "\n");
Regions.emplace_back(LastRegionEnd, Start, StackColoring::LiveRange());
LastRegionEnd = Start;
}
LLVM_DEBUG(dbgs() << " Creating new region: " << LastRegionEnd << " .. "
<< End << ", range " << Obj.Range << "\n");
Regions.emplace_back(LastRegionEnd, End, Obj.Range);
LastRegionEnd = End;
}
// Split starting and ending regions if necessary.
for (unsigned i = 0; i < Regions.size(); ++i) {
StackRegion &R = Regions[i];
if (Start > R.Start && Start < R.End) {
StackRegion R0 = R;
R.Start = R0.End = Start;
Regions.insert(&R, R0);
continue;
}
if (End > R.Start && End < R.End) {
StackRegion R0 = R;
R0.End = R.Start = End;
Regions.insert(&R, R0);
break;
}
}
// Update live ranges for all affected regions.
for (StackRegion &R : Regions) {
if (Start < R.End && End > R.Start)
R.Range.Join(Obj.Range);
if (End <= R.End)
break;
}
ObjectOffsets[Obj.Handle] = End;
}
void StackLayout::computeLayout() {
// Simple greedy algorithm.
// If this is replaced with something smarter, it must preserve the property
// that the first object is always at the offset 0 in the stack frame (for
// StackProtectorSlot), or handle stack protector in some other way.
// Sort objects by size (largest first) to reduce fragmentation.
if (StackObjects.size() > 2)
std::stable_sort(StackObjects.begin() + 1, StackObjects.end(),
[](const StackObject &a, const StackObject &b) {
return a.Size > b.Size;
});
for (auto &Obj : StackObjects)
layoutObject(Obj);
LLVM_DEBUG(print(dbgs()));
}