# Patent

## Title
Method for validation of binary code transformations

## Abstract

A method of validating binary code transformation in one aspect includes analyzing original program and transform program. Control flow graphs are generated for both programs. The two graphs are traversed to create respective linear invariant representations. The linear representations are compared to identify incorrect transformations.

## Background
FIELD OF THE INVENTION
The present disclosure relates to optimizing computer executable codes, and particularly to a method for validating binary code transformation.
BACKGROUND OF THE INVENTION
Optimizing executable code is a known technique to improve the performance of code that has already been linked and is ready for execution. It is typically performed using a runtime profile of the code. Different optimization techniques are available such as inlining and code restructuring, which transform the code to functionally equivalent form. If the code optimization does not correctly transform the code to functionally equivalent form, unpredictable consequences may result, such as a program crash.
While there are existing technologies that perform validations on program source code, semantics of compiler's internal representation of a code, or even hardware level code, those technologies are incapable of handling the kind of transformations performed on the binary applications. Thus, what is desirable is a method that helps to validate the correctness of binary code transformations.
BRIEF SUMMARY OF THE INVENTION
A method for validating binary code transformations is provided. In one aspect, the method may comprise analyzing binary code of an executable program to produce a sequence of basic units; generating control flow graph associated with the sequence of basic units; generating invariant linear function representation based on the control flow graph; analyzing optimized transformation of the executable program to produce a second sequence of basic units; generating second control flow graph associated with the second sequence of basic units; generating second invariant linear function representation based on the second control flow graph; comparing the invariant linear function representation and the second invariant linear function representation; and identifying one or more incorrect transformations in the optimized transformation.
A program storage device readable by a machine, tangibly embodying a program of instructions executable by the machine to perform the above method may also be provided.
Further features as well as the structure and operation of various embodiments are described in detail below with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a flow diagram illustrating a method for validating binary code transformation in one embodiment of the present disclosure.
FIG. 2 shows an example sequence of three basic blocks.
FIG. 3 shows the FCG for the basic blocks in FIG. 2.



DETAILED DESCRIPTION
The binary code of the original program and the transformed program are analyzed, using various available techniques such as static techniques using relocation information and/or dynamic techniques by intercepting execution and recognizing the accessed basic units, and a control flow graph for both programs is generated. For each validated function, the two graphs are both traversed in consistent fashion, creating their linear invariant textual representations. These linear representations can be compared as simple text strings in order to identify incorrect transformation.
FIG. 1 is a flow diagram illustrating a method for validating binary code transformation in one embodiment of the present disclosure. Steps 102, 104 and 106 are performed for both the original and the transformed codes. At 102, program analysis begins. The executable program is analyzed using the FDPR (Feedback Directed Program Restructuring) technology. Briefly, FDPR optimizes the executable image of a program by collecting information on the behavior of the program while the program is used for some typical workload, and then creating a new version of the program that is optimized for that workload. The principal output of this analysis is a sequence of basic units. Basic units are the smallest elements of the program that stay intact under every reordering. In this embodiment of the disclosure, the basic units include two types, basic blocks and data objects. The basic blocks type includes instructions. The data objects type includes data, for example, read-only and writable. Data objects correspond to the high-level data objects defined in the source program, for example, arrays, structures, or scalars. A basic block is a sequence of instructions that can be entered only at its beginning and exited only at its end. FIG. 2 shows an example sequence of three basic blocks 202, 204, 206, of which two 202, 204 are adjacent.
Referring back to FIG. 1, at 104, building a program control flow graph (CFG) begins. In one embodiment, building the CFG is done by connecting, with a directed edge, the exit point of each basic block A to the entry points of the basic blocks according to the way A terminates. For instance, if A terminates by a simple branch, connect to the target of the branch. If A terminates by a conditional branch, connect to both the target of the branch, as well as the following basic block (called the fall-through basic block). If A terminates by an indirect branch keep A unconnected at the moment, as the target is not known at this moment. FIG. 3 shows the CFG for the basic blocks in FIG. 2.
An edge in the CFG carries an execution count, that is, the number of times control passed along that edge when the program was executed. This information can be collected by various means, for example, the “pixie” tool, or the basic block profiling provided by standard compilers like GCC. An edge that carries relatively high execution count is termed hot edge. A basic block that executes many times relative to the average count is termed hot basic block.
Referring back to FIG. 1, at 106, invariant linear function representation is created by consistently traversing the CFG. This step forms an invariant linear representation for a given function. Invariant representation refers to one or more invariants under a set of predefined optimization transformations of the function. An optimization transformation is a transformation of the code that preserves the semantics of the function while providing some potential improvement, typically in execution time.
The basic set of transformations includes at least code restructuring, function inlining, and hot-cold code motion. Code restructuring is an optimization, which places basic blocks close to each other if they are connected by relatively hot edges. For example, basic block A (shown in FIG. 2 and FIG. 3) ends with a BNE branch (branch of not equal), following basic block B, for the EQ condition. Under code restructuring, if the edge A-C is much hotter then A-B, the condition that ends A might be changed to EQ (that is, BEQ) so that basic block C will be the fall-through basic block A. Similarly, basic blocks that connect by edges with cold branches may be placed far from each other, sometimes requiring an additional intermediate branch in between if the distance is too great for the original branch to be performed in one hop.
Function inlining replaces the call instruction by a copy of the function in places where the call instruction is very hot. Hot-cold code motion optimization moves instructions from hot basic block to a colder one, making sure these instructions are properly replicated to preserve the semantics.
The following algorithm is used to create an invariant linear representation of a function in one embodiment. The representation is in a form of a sequence of strips A strip is a possible path through the program CFG, that is, a trace of non-branch instructions that may execute sequentially when the program runs.
Function CreateInvariantRepresentation (ControlFlowGraph cfg Function f)

    
    
        // Control Flow Graph cfgis the CFG of the program
        // Node f is the entry point of the give
        Stack returnStack=<empty>// a stack of nodes in cfg
        Stack entryPointStack=<empty>// a stack of nodes in cfg
        List stripList=<empty>// the output list of strips.
        Node epf=EntryPoint(f)
    
    


Push(epf, entryPointStack)

    
    
        wile entryPointStackis not empty do
        
            ep=Pop(entryPointStack)
            If ep has not been traversed then
            
                strip=Traverse(ep, returnStack, entryPointStack)
                Add(strip, stripList)
            
            
            End if
        
        
        End while
        Return stripList

End function

    
    


Function Traverse (Node entry, InputOutput Stack returnStack, InputOutput Stack entryPointStack)

    
    
        List Strip=<empty>// output strip (list of instructions)
        Node bb entry, firstBB, secondBB
        While bb is not <empty> do
        
            // add basic block to strip
            Foreach Instruction instr in BasicBlock(bb) do
            
                Add(instr, Strip)
            
            
            End foreach
            Mark bb as traversed
            // sechedule BBs at edges of bb
            Bool firstIsCall (Edge(bb, First) is a call)
            firstBB=RetrieveNode(Edge(bb, First), returnStack)
            If firstBB is not <empty> then
            
                secondBB=RerieveNode(Edge(bb, Second), returnStack)
            
            
            Else
            
                firstBB=RetrieveNode(Edgeb, Second), returnStack)
                secondBB=<empty>
            
            
            End if
            If firstBB is not <empty> then
            
                if secondBB is not <empty> then
                
                    // schedule second node. If this is a call edge, push called
                
                
                function's entry point node on return stack
                
                    // else push node on entry point stack
                    Stack stack=firstIsCall? returnStack: entryPointStack;
                    Push(secondBB, stack)
                
                
                End if
            
            
            End if
            bb=firstBB
        
        
        End while
        // reached a traversed node or end of function
        Return strips

End function

    
    


Function RetrieveNode(Edge edge, InputOutput Stack returnStack)

    
    
        Node retrievedBB=<empty>
        If edge exists and is direct then
        
            // continue traversing this function
            retrievedBB=Node(edge)
        
        
        Else if edge is a return instruction (e.g. ‘blr’ in POWER arch.) then
        
            // traverse back to caller
            retrievedBB=Pop(returnStack)
        
        
        End if
        // do not proceed in this direction if node has been traversed already
        If retievedBB is not <empty> and retriebedBB is not traversed then
        
            Return retrievedBB
        
        
        Else
        
            Return <empty>
        
        
        End if

End function

    
    


An example strip follows. In the example, the branch instructions, which are not part of the strips, are commented out.












Strip 6:


#13b2b29c . . .










#
41 86 00 48
beq-
cr1,13b2b2e4 <.pevm_EXECC+0x504>







#13b2b2e4 . . .











e8 7d 00 08
ld
r3,8(r29)



28 9b 05 7b
cmplwic
r1,r27,1403











e8 63 00 c8
ld
r3,200(r3)



80 03 00 9c
lwz
r0,156(r3)



70 00 00 40
andi.
r0,r0,64










#
41 82 00 14
beq-
13b2b30c <.pevm_EXECC+0x52c>







#13b2b30c . . .











a0 1c 00 34
lhz
r0,52(r28)



70 03 00 40
andi.
r3,r0,64


#
40 82 00 34
bne-
13b2b348 <.pevm_EXECC+0x568>



80 bc 00 50
lwz
r5,80(r28)



e8 dc 00 56
lwa
r6,84(r28)



e8 7d 00 08
ld
r3,8(r29)



e8 9d 00 88
ld
r4,136(r29)



39 20 00 00
li
r9,0



e8 63 00 00
ld
r3,0(r3)



38 e0 00 00
li
r7,0



39 00 00 00
li
r8,0



e8 84 00 00
ld
r4,0(r4)


#
4b 9f ed 45
bl
1352a080 <.kgicls>



60 00 00 00
nop



a0 1c 00 34
lhz
r0,52(r28)



54 00 04 3c
rlwinm
r0,r0,0,16,30



80 7c 00 58
lwz
r3,88(r28)



2c 23 00 00
cmpdi
r3,0



b0 1c 00 34
sth
r0,52(r28)


#
41 82 00 0c
beq-
13b2b364 <.pevm_EXECC+0x584>







#13b2b364 . . .











7f a3 eb 78
mr
r3,r29



7f 64 db 78
mr
r4,r27


#
4b fe 8b b5
bl
13b13f20





<.pevm_handle_external_error>



60 00 00 00
nop


#
48 00 01 34
b
13b2b4a8 <.pevm_EXECC+0x6c8>







Strip 7:


#13b2b35c . . .











e8 7d 00 b0
ld
r3,176(r29)



93 c3 00 98
stw
r30,152(r3)







Strip 8:


#13b2b2fc . . .










#
40 86 00 10
bne-
cr1,13b2b30c <.pevm_EXECC+0x52c>



7f a3 eb 78
mr
r3,r29


#
4b fe 9e 9d
bl
13b151a0 <.pfrfoe_flush_oci_error>



60 00 00 00
nop









At 108, the generated strips of two implementations of a function are compared. The comparison can be a textual or character-by-character comparison. Incorrect transformations are identified from the comparison. For example, the strip or strips corresponding to the transformed or optimized code that do not match the strip or strips of the original code are identified as being incorrect.
The system and method of the present disclosure may be implemented and run on a general-purpose computer or computer system. The computer system may be any type of known or will be known systems and may typically include a processor, memory device, a storage device, input/output devices, internal buses, and/or a communications interface for communicating with other computer systems in conjunction with communication hardware and software, etc.
The terms “computer system” and “computer network” as may be used in the present application may include a variety of combinations of fixed and/or portable computer hardware, software, peripherals, and storage devices. The computer system may include a plurality of individual components that are networked or otherwise linked to perform collaboratively, or may include one or more stand-alone components. The hardware and software components of the computer system of the present application may include and may be included within fixed and portable devices such as desktop, laptop, and server A module may be a component of a device, software, program, or system that implements some “functionality”, which can be embodied as software, hardware, firmware, electronic circuitry, or etc.
The embodiments described above are illustrative examples and it should not be construed that the present invention is limited to these particular embodiments. Thus, various changes and modifications may be effected by one skilled in the art without departing from the spirit or scope of the invention as defined in the appended claims.

## Claims

1. A computer-implemented method for validating binary code transformations, comprising:
analyzing binary code of an executable program to produce a sequence of basic units comprising smallest elements of the executable program that stay intact under every reordering;
generating control flow graph associated with the sequence of basic units;
generating invariant linear function representation based on the control flow graph;
analyzing optimized transformation of the executable program to produce a second sequence of basic units;
generating second control flow graph associated with the second sequence of basic units;
generating second invariant linear function representation based on the second control flow graph;
comparing the invariant linear function representation and the second invariant linear function representation; and
identifying one or more incorrect transformations in the optimized transformation,
wherein the invariant linear function representation and the second invariant linear function representation are invariants under a set of predefined optimization transformation and include a sequence of strips comprising a path through a trace of non-branch instructions executing sequentially when the executable program runs.