dynamic compilation and modification cs 671 april 15, 2008

Dynamic Compilation and Modification

CS 671April 15, 2008

2 CS 671 – Spring 2008

So Far… Static Compilation

CompilerHigh-Level

Programming Languages

Machine Code

Error Messages

High-Level Programming Languages

Machine Code

FrontEnd

BackEnd

Error Messages

CompilerDigging Deeper…

3 CS 671 – Spring 2008

Alternatives to the Traditional Model

Static Compilation

All work is done “ahead-of-time”

Just-in-Time Compilation

Postpone some compilation tasks

Multiversioning and Dynamic Feedback

Include multiple options in binary

Dynamic Binary Optimization

Traditional compilation model

Executables can adapt

4 CS 671 – Spring 2008

Move More of Compilation to Run Time

Execution environment may be quite different from the assumptions made at compile time

•Dynamically loaded libraries

•User inputs

•Hardware configurations

•Dependence on software vendors

•Apps on tap

•Incorporate profiling

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High-Level Programming Languages

Machine Code

FrontEnd

BackEnd

Error Messages

Ship bytecodes (think IR) rather than binaries• Binaries execute on machines• Bytecodes execute on virtual machines

Compiler

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javac the Java bytecode compiler

java the Java virtual machine

Bytecode: machine independent, portable

Step One: “Compile” Circle.java% javac Circle.java -> Circle.class

Step Two: “Execute”% java Circle.class

javacsource bytecode

javabytecode execute

7 CS 671 – Spring 2008

Each frame contains local variables and an operand stack

Instruction set• Load/store between locals and operand stack• Arithmetic on operand stack• Object creation and method invocation• Array/field accesses• Control transfers and exceptions

The type of the operand stack at each program point is known at compile time

Bytecodes

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Example:

iconst 2iload aiload biaddimulistore c

Computes: c := 2 * (a + b)

Bytecodes (cont.)

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Example:



a

b

c

42

7

0

Bytecodes (cont.)

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Example:



a

b

c

42

7

0

2

Bytecodes (cont.)

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Example:



a

b

c

42

7

0 42

2

Bytecodes (cont.)

12 CS 671 – Spring 2008

Example:



a

b

c

42

7

0

7

42

2

Bytecodes (cont.)

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Example:



a

b

c

42

7

0 49

2

Bytecodes (cont.)

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Example:



a

b

c

42

7

0

98

Bytecodes (cont.)

15 CS 671 – Spring 2008

Example:



a

b

c

42

7

98

Bytecodes (cont.)

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Executing Bytecode

java Circle.class - What happens?

Interpreting

• map each bytecode to a machine code sequence,

• for each bytecode, execute the sequence

Translation to machine code

• map all the bytecodes to machine code (or a higher level intermediate representation)

• massage them (e.g., remove redundancies)

• execute the machine code

17 CS 671 – Spring 2008

Hotspot Compilation

A hybrid approach

• Initially interpret

• Find the “hot” (frequently executed) methods

• Translate only hot methods to machine code

18 CS 671 – Spring 2008

The Virtual Machine

An extreme version of an old idea

Previously:

Now:

MyApp

x86

P III P IV

MyApp

alpha

21164 21264

MyApp

pa-risc

PA-8000 PA-7000

MyApp

JVM

P III P IV 21164 21264 PA-8000 PA-7000VM VM VM VM VM VM

19 CS 671 – Spring 2008

Compile-Time Multiversioning

• Multiple versions of code sections are generated at compile-time

• Most appropriate variant is selected at runtime based upon characteristics of the input data and/or machine environment

• Multiple variants can cause code explosion

– Thus typically only a few versions are created

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Another Alternative

Modify a traditional application as it executes

Why?• Don’t have source code!

????binary modified binary

21 CS 671 – Spring 2008

A Dynamic Optimization System?

Transforms* an application at run time

* {translate, optimize, extend}

Application

Transform

CodeCache

Execute

Profile

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Classification

Dynamic binary optimizers (x86 x86opt)• Complement the static compiler

– User inputs, phases, DLLs, hardware features– Examples: DynamoRIO, Mojo, Strata

Dynamic translators (x86 PPC)• Convert applications to run on a new architecture

– Examples: Rosetta, Transmeta CMS, DAISY

Binary instrumentation (x86 x86instr)• Inspect and/or add features to existing

applications– Examples: Pin, Valgrind

JITs + adaptive systems (Java bytecode x86)

23 CS 671 – Spring 2008

Dynamic Instrumentation Demo

Pin• Four architectures – IA32, EM64T, IPF, XScale• Four OSes – Linux, FreeBSD, MacOS, Windows

24 CS 671 – Spring 2008

What is Instrumentation?

A technique that inserts extra code into a program to collect runtime information

Instrumentation approaches:

• Source instrumentation:

– Instrument source programs

• Binary instrumentation:– Instrument executables directly

25 CS 671 – Spring 2008

No need to recompile or relink Discover code at runtime Handle dynamically-generated code Attach to running processes

Why use Dynamic Instrumentation?

26 CS 671 – Spring 2008

How is Instrumentation used in PL/Compiler Research?

Program analysis– Code coverage– Call-graph generation– Memory-leak detection– Instruction profiling

Thread analysis– Thread profiling– Race detection

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•Trace Generation

•Branch Predictor and Cache Modeling

•Fault Tolerance Studies

•Emulating Speculation

•Emulating New Instructions

How is Instrumentation used in Computer Architecture Research?

28 CS 671 – Spring 2008

Pin Features

Dynamic Instrumentation:• Do not need source code, recompilation, post-linking

Programmable Instrumentation:• Provides rich APIs to write in C/C++ your own instrumentation

tools (called Pintools)

Multiplatform:• Supports x86, x86-64, Itanium, Xscale• Supports Linux, Windows, MacOS

Robust:• Instruments real-life applications: Database, web browsers, …• Instruments multithreaded applications• Supports signals

Efficient:• Applies compiler optimizations on instrumentation code

29 CS 671 – Spring 2008

Using Pin

Launch and instrument an application $ pin –t pintool –- application

Instrumentation engine (provided in the kit)

Instrumentation tool

(write your own, or use one provided in the kit)

Attach to and instrument an application $ pin –t pintool –pid 1234

30 CS 671 – Spring 2008

Pin Instrumentation APIs

Basic APIs are architecture independent:• Provide common functionalities like determining:

– Control-flow changes– Memory accesses

Architecture-specific APIs• e.g., Info about segmentation registers on IA32

Call-based APIs:• Instrumentation routines• Analysis routines

31 CS 671 – Spring 2008

Instrumentation vs. Analysis

Instrumentation routines define where instrumentation is inserted• e.g., before instruction Occurs first time an instruction is executed

Analysis routines define what to do when instrumentation is activated• e.g., increment counter Occurs every time an instruction is executed

32 CS 671 – Spring 2008

Pintool 1: Instruction Count

sub $0xff, %edx

cmp %esi, %edx

jle <L1>

mov $0x1, %edi

add $0x10, %eax

counter++;

counter++;

counter++;

counter++;

counter++;

33 CS 671 – Spring 2008

Pintool 1: Instruction Count Output

$ /bin/ls Makefile imageload.out itrace proccount imageload inscount0 atrace itrace.out

$ pin -t inscount0.so -- /bin/ls Makefile imageload.out itrace proccount imageload inscount0 atrace itrace.out

Count 422838

34 CS 671 – Spring 2008

ManualExamples/inscount0.cpp

instrumentation routine

analysis routine

#include <iostream>#include "pin.h"

UINT64 icount = 0;

void docount() { icount++; } void Instruction(INS ins, void *v) { INS_InsertCall(ins, IPOINT_BEFORE, (AFUNPTR)docount, IARG_END);}

void Fini(INT32 code, void *v) { std::cerr << "Count " << icount << endl; }

int main(int argc, char * argv[]){ PIN_Init(argc, argv); INS_AddInstrumentFunction(Instruction, 0); PIN_AddFiniFunction(Fini, 0); PIN_StartProgram(); return 0;}

35 CS 671 – Spring 2008

Pintool 2: Instruction Trace

sub $0xff, %edx

cmp %esi, %edx

jle <L1>

mov $0x1, %edi

add $0x10, %eax

Print(ip);

Print(ip);

Print(ip);

Print(ip);

Print(ip);

Need to pass ip argument to the analysis routine (printip())

36 CS 671 – Spring 2008

Pintool 2: Instruction Trace Output

$ pin -t itrace.so -- /bin/ls Makefile imageload.out itrace proccount imageload inscount0 atrace itrace.out

$ head -4 itrace.out 0x40001e90 0x40001e91 0x40001ee4 0x40001ee5

37 CS 671 – Spring 2008

ManualExamples/itrace.cpp

argument to analysis routine

analysis routineinstrumentation routine

#include <stdio.h>#include "pin.H"FILE * trace;void printip(void *ip) { fprintf(trace, "%p\n", ip); }

void Instruction(INS ins, void *v) { INS_InsertCall(ins, IPOINT_BEFORE, (AFUNPTR)printip, IARG_INST_PTR, IARG_END);}void Fini(INT32 code, void *v) { fclose(trace); }int main(int argc, char * argv[]) { trace = fopen("itrace.out", "w"); PIN_Init(argc, argv); INS_AddInstrumentFunction(Instruction, 0);

PIN_AddFiniFunction(Fini, 0); PIN_StartProgram(); return 0;}

38 CS 671 – Spring 2008

Examples of Arguments to Analysis Routine

IARG_INST_PTR• Instruction pointer (program counter) value

IARG_UINT32 <value>• An integer value

IARG_REG_VALUE <register name>• Value of the register specified

IARG_BRANCH_TARGET_ADDR• Target address of the branch instrumented

IARG_MEMORY_READ_EA• Effective address of a memory read

And many more … (refer to the Pin manual for details)

39 CS 671 – Spring 2008

Instrumentation Points

Instrument points relative to an instruction:

• Before (IPOINT_BEFORE)• After:

– Fall-through edge (IPOINT_AFTER)– Taken edge (IPOINT_TAKEN_BRANCH)

cmp %esi, %edx

jle <L1>

mov $0x1, %edi

<L1>: mov $0x8,%edi

count()

count()

count()

40 CS 671 – Spring 2008

• Instruction• Basic block

– A sequence of instructions terminated at a control-flow changing instruction

– Single entry, single exit• Trace

– A sequence of basic blocks terminated at an unconditional control-flow changing instruction

– Single entry, multiple exits

Instrumentation Granularity

sub $0xff, %edxcmp %esi, %edxjle <L1>

mov $0x1, %ediadd $0x10, %eaxjmp <L2>1 Trace, 2 BBs, 6

insts

Instrumentation can be done at three different granularities:

41 CS 671 – Spring 2008

Pintool 3: Faster Instruction Count

sub $0xff, %edx

cmp %esi, %edx

jle <L1>

mov $0x1, %edi

add $0x10, %eax

counter += 3

counter += 2basic blocks (bbl)

42 CS 671 – Spring 2008

Modifying Program Behavior

Pin allows you not only to observe but also change program behavior

Ways to change program behavior:

• Add/delete instructions

• Change register values

• Change memory values

• Change control flow

Pin Internals

44 CS 671 – Spring 2008

Pin’s Software Architecture

JIT Compiler

Emulation Unit

Virtual Machine (VM)

Code

Cache

Instrumentation APIs

Ap

pli

cati

on

Operating SystemHardware

PinPintool

Address space

45 CS 671 – Spring 2008

Dynamic Instrumentation

Original codeCode cache

Pin fetches trace starting block 1 and start instrumentation

7’

2’

1’

Pin

2 3

1

7

45

6

Exits point back to Pin

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Pin transfers control intocode cache (block 1)

2 3

1

7

45

67’

2’

1’

Pin

47 CS 671 – Spring 2008



7’

2’

1’

PinPin fetches and instrument a new trace

6’

5’

3’trace linking

2 3

1

7

45

6

48 CS 671 – Spring 2008

Implementation Challenges

• Linking– Straightforward for direct branches– Tricky for indirects, invalidations

• Re-allocating registers

• Maintaining transparency

• Self-modifying code

• Supporting MT applications…

49 CS 671 – Spring 2008

Thread-safe accesses Pin, Pintool, and App– Pin: One thread in the VM at a time– Pintool: Locks, ThreadID, event notification– App: Thread-local spill area

Providing pthreads functions to instrumentation tools

Pin’s Multithreading Support

Pintool

Application

System’s libpthread signal handlersignal handler

set up signal

handlers

Pin’s mini-libpthread

Redirect all other pthreads function calls to application’s libpthread

50 CS 671 – Spring 2008

Pin Overhead

SPEC Integer 2006

100%

120%

140%

160%

180%

200%

perlb

ench

sjen

g

xala

ncbm

k

gobm

k

gcc

h264

ref

omne

tpp

bzip

2

libqu

antu

m mcf

asta

r

hmm

er

Rel

ativ

e to

Nat

ive

51 CS 671 – Spring 2008

Adding User Instrumentation

100%

200%

300%

400%

500%

600%

700%

800%

perlb

ench

sjen

g

xala

ncbm

k

gobm

k

gcc

h264

ref

omne

tpp

bzip

2

libqu

antu

m mcf

asta

r

hmm

er

Rel

ativ

e to

Nat

ive Pin

Pin+icount

52 CS 671 – Spring 2008

Dynamic Optimization Summary

Complement the static compiler• Shouldn’t compete with static compilers• Observe execution pattern• Optimize frequently executed code

– Optimization overhead could degrade performance

Exploits opportunities• Arise only at runtime

– DLLs– Runtime constants– Hardware features, user patterns, etc.

• Too expensive to fully exploit statically– Path-sensitive optimizations

dynamic compilation and modification cs 671 april 15, 2008

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