forked from llvm/llvm-project
-
Notifications
You must be signed in to change notification settings - Fork 1
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
Merge pull request #17 from connorkuehl/port-randomization
Add (port) performance sensitive randomization
- Loading branch information
Showing
4 changed files
with
254 additions
and
14 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,217 @@ | ||
//===----- LayoutFieldRandomizer.cpp - Randstruct Implementation -*- C++ | ||
//-*-===// | ||
// | ||
// 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 | ||
// | ||
//===----------------------------------------------------------------------===// | ||
// | ||
// Cache line best-effort field randomization | ||
// | ||
//===----------------------------------------------------------------------===// | ||
|
||
#include "LayoutFieldRandomizer.h" | ||
#include "llvm/ADT/SmallVector.h" | ||
|
||
#include <algorithm> | ||
#include <cstdint> | ||
#include <random> | ||
#include <vector> | ||
|
||
namespace clang { | ||
|
||
/// Bucket to store fields up to size of a cache line during randomization. | ||
class Bucket { | ||
public: | ||
virtual ~Bucket() = default; | ||
/// Returns a randomized version of the bucket. | ||
virtual SmallVector<FieldDecl *, 64> randomize(); | ||
/// Checks if an added element would fit in a cache line. | ||
virtual bool canFit(size_t size) const; | ||
/// Adds a field to the bucket. | ||
void add(FieldDecl *field, size_t size); | ||
/// Is this bucket for bitfields? | ||
virtual bool isBitfieldRun() const; | ||
/// Is this bucket full? | ||
bool full() const; | ||
bool empty() const; | ||
|
||
protected: | ||
size_t size; | ||
SmallVector<FieldDecl *, 64> fields; | ||
}; | ||
|
||
/// BitfieldRun is a bucket for storing adjacent bitfields that may | ||
/// exceed the size of a cache line. | ||
class BitfieldRun : public Bucket { | ||
public: | ||
virtual SmallVector<FieldDecl *, 64> randomize() override; | ||
virtual bool canFit(size_t size) const override; | ||
virtual bool isBitfieldRun() const override; | ||
}; | ||
|
||
// TODO: Is there a way to detect this? (i.e. on 32bit system vs 64?) | ||
const size_t CACHE_LINE = 64; | ||
|
||
SmallVector<FieldDecl *, 64> Bucket::randomize() { | ||
// TODO use seed | ||
auto rng = std::default_random_engine{}; | ||
std::shuffle(std::begin(fields), std::end(fields), rng); | ||
return fields; | ||
} | ||
|
||
bool Bucket::canFit(size_t size) const { | ||
// We will say we can fit any size if the bucket is empty | ||
// because there are many instances where a field is much | ||
// larger than 64 bits (i.e., an array, a structure, etc) | ||
// but it still must be placed into a bucket. | ||
// | ||
// Otherwise, if the bucket has elements and we're still | ||
// trying to create a cache-line sized grouping, we cannot | ||
// fit a larger field in here. | ||
return empty() || this->size + size <= CACHE_LINE; | ||
} | ||
|
||
void Bucket::add(FieldDecl *field, size_t size) { | ||
fields.push_back(field); | ||
this->size += size; | ||
} | ||
|
||
bool Bucket::isBitfieldRun() const { | ||
// The normal bucket is not a bitfieldrun. This is to avoid RTTI. | ||
return false; | ||
} | ||
|
||
bool Bucket::full() const { | ||
// We're full if our size is a cache line. | ||
return size >= CACHE_LINE; | ||
} | ||
|
||
bool Bucket::empty() const { return size == 0; } | ||
|
||
SmallVector<FieldDecl *, 64> BitfieldRun::randomize() { | ||
// Keep bit fields adjacent, we will not scramble them. | ||
return fields; | ||
} | ||
|
||
bool BitfieldRun::canFit(size_t size) const { | ||
// We can always fit another adjacent bitfield. | ||
return true; | ||
} | ||
|
||
bool BitfieldRun::isBitfieldRun() const { | ||
// Yes. | ||
return true; | ||
} | ||
|
||
SmallVector<Decl *, 64> randomize(SmallVector<Decl *, 64> fields) { | ||
auto rng = std::default_random_engine{}; | ||
std::shuffle(std::begin(fields), std::end(fields), rng); | ||
return fields; | ||
} | ||
|
||
SmallVector<Decl *, 64> perfrandomize(const ASTContext &ctx, | ||
SmallVector<Decl *, 64> fields) { | ||
// All of the buckets produced by best-effort cache-line algorithm. | ||
std::vector<std::unique_ptr<Bucket>> buckets; | ||
|
||
// The current bucket of fields that we are trying to fill to a cache-line. | ||
std::unique_ptr<Bucket> currentBucket = nullptr; | ||
// The current bucket containing the run of adjacent bitfields to ensure | ||
// they remain adjacent. | ||
std::unique_ptr<Bucket> currentBitfieldRun = nullptr; | ||
|
||
// Tracks the number of fields that we failed to fit to the current bucket, | ||
// and thus still need to be added later. | ||
size_t skipped = 0; | ||
|
||
while (!fields.empty()) { | ||
// If we've skipped more fields than we have remaining to place, | ||
// that means that they can't fit in our current bucket, and we | ||
// need to start a new one. | ||
if (skipped >= fields.size()) { | ||
skipped = 0; | ||
buckets.push_back(std::move(currentBucket)); | ||
} | ||
|
||
// Take the first field that needs to be put in a bucket. | ||
auto field = fields.begin(); | ||
auto *f = llvm::cast<FieldDecl>(*field); | ||
|
||
if (f->isBitField()) { | ||
// Start a bitfield run if this is the first bitfield | ||
// we have found. | ||
if (!currentBitfieldRun) { | ||
currentBitfieldRun = llvm::make_unique<BitfieldRun>(); | ||
} | ||
|
||
// We've placed the field, and can remove it from the | ||
// "awaiting buckets" vector called "fields" | ||
currentBitfieldRun->add(f, 1); | ||
fields.erase(field); | ||
} else { | ||
// Else, current field is not a bitfield | ||
// If we were previously in a bitfield run, end it. | ||
if (currentBitfieldRun) { | ||
buckets.push_back(std::move(currentBitfieldRun)); | ||
} | ||
// If we don't have a bucket, make one. | ||
if (!currentBucket) { | ||
currentBucket = llvm::make_unique<Bucket>(); | ||
} | ||
|
||
// FIXME get access to AST Context | ||
auto width = ctx.getTypeInfo(f->getType()).Width; | ||
|
||
// If we can fit, add it. | ||
if (currentBucket->canFit(width)) { | ||
currentBucket->add(f, width); | ||
fields.erase(field); | ||
|
||
// If it's now full, tie off the bucket. | ||
if (currentBucket->full()) { | ||
skipped = 0; | ||
buckets.push_back(std::move(currentBucket)); | ||
} | ||
} else { | ||
// We can't fit it in our current bucket. | ||
// Move to the end for processing later. | ||
++skipped; // Mark it skipped. | ||
fields.push_back(f); | ||
fields.erase(field); | ||
} | ||
} | ||
} | ||
|
||
// Done processing the fields awaiting a bucket. | ||
|
||
// If we were filling a bucket, tie it off. | ||
if (currentBucket) { | ||
buckets.push_back(std::move(currentBucket)); | ||
} | ||
|
||
// If we were processing a bitfield run bucket, tie it off. | ||
if (currentBitfieldRun) { | ||
buckets.push_back(std::move(currentBitfieldRun)); | ||
} | ||
|
||
auto rng = std::default_random_engine{}; | ||
std::shuffle(std::begin(buckets), std::end(buckets), rng); | ||
|
||
// Produce the new ordering of the elements from our buckets. | ||
SmallVector<Decl *, 64> finalOrder; | ||
for (auto &bucket : buckets) { | ||
auto randomized = bucket->randomize(); | ||
finalOrder.insert(finalOrder.end(), randomized.begin(), randomized.end()); | ||
} | ||
|
||
return finalOrder; | ||
} | ||
|
||
SmallVector<Decl *, 64> rearrange(const ASTContext &ctx, | ||
SmallVector<Decl *, 64> fields) { | ||
return perfrandomize(ctx, fields); | ||
} | ||
|
||
} // namespace clang |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,27 @@ | ||
//===----- LayoutFieldRandomizer.h - Entry Point for Randstruct --*- C++ | ||
//-*-===// | ||
// | ||
// 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 header file provides the entry point for the Randstruct structure | ||
// layout randomization code. | ||
// | ||
//===----------------------------------------------------------------------===// | ||
|
||
#ifndef LLVM_CLANG_LIB_AST_LAYOUTFIELDRANDOMIZER_H | ||
#define LLVM_CLANG_LIB_AST_LAYOUTFIELDRANDOMIZER_H | ||
|
||
#include "clang/AST/AST.h" | ||
|
||
namespace clang { | ||
/// Rearranges the order of the supplied fields. Will make best effort to fit | ||
// members into a cache line. | ||
SmallVector<Decl *, 64> rearrange(const ASTContext &ctx, | ||
SmallVector<Decl *, 64> fields); | ||
} // namespace clang | ||
|
||
#endif |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters