footprint analysis: a shape analysis that discovers preconditions

Footprint Analysis: A Shape Analysis that Discovers

Preconditions

Hongseok Yang(Queen Mary, University of London)

(Joint work with Cristiano Calcagno, Dino Distefano, and Peter O’Hearn)

void XXX_CancelIrp(PDEVICE_OBJECT DeviceObject, PIRP Irp){ ……… PRESET_IRP ResetIrp,temp,tempnext; PDEVICE_EXTENSION de; ……… KeAcquireSpinLock(&de->ResetSpinLock, &Irql); ResetIrp = (PRESET_IRP)de->Flink2; while (ResetIrp !=NULL) { if (ResetIrp->Irp == Irp) { temp = (PRESET_IRP)de; tempnext = temp->Flink2; while (tempnext != ResetIrp) { temp = tempnext; tempnext = temp->Flink2; } temp->Flink2 = ResetIrp->Flink2; free(ResetIrp); break; } else if (ResetIrp->Flink2 == (PRESET_IRP)de) break; else ResetIrp = (PRESET_IRP)ResetIrp->Flink2; } KeReleaseSpinLock(&de->ResetSpinLock, Irql); …… IoCompleteRequest(Irp, IO_NO_INCREMENT);}

void XXX_CancelIrp(PDEVICE_OBJECT DeviceObject, PIRP Irp)

KeReleaseSpinLock(&de->ResetSpinLock, Irql);

KeAcquireSpinLock(&de->ResetSpinLock, &Irql);

IoCompleteRequest(Irp, IO_NO_INCREMENT);


Footprint Analysis

• Discovers safe preconditions of a piece of code. • Only the memory footprint of the code.

void XXX_CancelIrp(PDEVICE_OBJECT DeviceObject, PIRP Irp){ ……… PXXX_RESET_IRP XXXResetIrp,temp,tempnext; PDEVICE_EXTENSION deviceExtension; ……… KeAcquireSpinLock(&deviceExtension->ResetSpinLock, &Irql); ResetIrp = (PRESET_IRP)de->Flink2; while (ResetIrp !=NULL) { if (ResetIrp->Irp == Irp) { temp = (PRESET_IRP)de; tempnext = temp->Flink2; while (tempnext != ResetIrp) { temp = tempnext; tempnext = temp->Flink2; } temp->Flink2 = ResetIrp->Flink2; free(ResetIrp); break; } else if (ResetIrp->Flink2 == (PRESET_IRP)de) break; else ResetIrp = (PRESET_IRP)ResetIrp->Flink2; } KeReleaseSpinLock(&deviceExtension->ResetSpinLock, Irql); …… IoCompleteRequest(Irp, IO_NO_INCREMENT);}

(de aD Flink2: x0) * ls (RESET_IRP,Flink2) (x0,de)

typedef struct { RESET_IRP* Flink2; IRP* Irp;…} RESET_IRP, *PRESET_IRP;

typedef struct { RESET_IRP* Flink2; …} DEVICE_EXTENSION;

(de aD Flink2: x0) * ls (RESET_IRP,Flink2) (x0,x1) * (x1aR Irp:Irp)

(de aD Flink2: x0) * ls (RESET_IRP,Flink2) (x0,0)

(de aD Flink2: x0) * ls (RESET_IRP,Flink2) (x0,de)(de aD Flink2: de)

(de aD Flink2:0)

void XXX_CancelIrp(PDEVICE_OBJECT DeviceObject, PIRP Irp){ ……… PXXX_RESET_IRP XXXResetIrp,temp,tempnext; PDEVICE_EXTENSION deviceExtension; ……… KeAcquireSpinLock(&deviceExtension->ResetSpinLock, &Irql); ResetIrp = (PRESET_IRP)de->Flink2; while (ResetIrp !=NULL) { if (ResetIrp->Irp == Irp) { temp = (PRESET_IRP)de; tempnext = temp->Flink2; while (tempnext != ResetIrp) { temp = tempnext; tempnext = temp->Flink2; } temp->Flink2 = ResetIrp->Flink2; free(ResetIrp); break; } else if (ResetIrp->Flink2 == (PRESET_IRP)de) break; else ResetIrp = (PRESET_IRP)BusResetIrp->Flink2; } KeReleaseSpinLock(&deviceExtension->ResetSpinLock, Irql); …… IoCompleteRequest(Irp, IO_NO_INCREMENT);}



de aD Flink2: de





(de aD Flink2:0)




de aD Flink2: deÆ de = ResetIrp





(de aD Flink2:0)




de aD Flink2: deÆ de = ResetIrp

ERROR: No IRP Field in DEVICE_EXTENSION





(de aD Flink2:0)

Footprint Analysis

Seeding

FootprintComputation

list t*;while (x!=0) {

t = x;

x = x->next;

free(t);

}

x=aÆemp

Footprint Analysis

Seeding



t = x;

x = x->next;

free(t);

}

x=aÆemp

P2 P3P1

Footprint Analysis

Seeding



t = x;

x = x->next;

free(t);

}

x=aÆemp

SpaceInvader

{P1}

{Q1,Q2}

{I1,I2,I3}

{P1}C{Q1ÇQ2}

P2 P3P1

Footprint Analysis

Seeding



t = x;

x = x->next;

free(t);

}

x=aÆemp

SpaceInvader

{P2}

{Q10,Q11 ,Q12}

{I10,I11,I12}

{P1}C{Q1ÇQ2}

P2 P3P1

{P2}C{Q10ÇQ11ÇQ12}

Footprint Analysis

Seeding



t = x;

x = x->next;

free(t);

}

x=aÆemp

SpaceInvader

{P3}

{P1}C{Q1ÇQ2}

P2 P3P1

{P2}C{Q10ÇQ11ÇQ12}

>

>

Footprint Analysis

Seeding



t = x;

x = x->next;

free(t);

}

x=aÆemp

SpaceInvader

{P1}C{Q1ÇQ2}

P2 P3P1

{P2}C{Q10ÇQ11ÇQ12}

Footprint Analysis

Safe precondition

Footprint only

Seeding


SpaceInvader

Separation Logic

xay, ls (y,z)

xay * ls (y,z), emp

9y’. z!=0 Æ v=a Æ xay’ * ls (y’,z)

x y y z

y zx

Variable Convention

• Program variables: x,y,z,t,v,w• Ghost (or auxiliary) variables: a,b,c,d,….• Primed variables: x’,y’,z’,t’,v’,w’

9 w’,w’1.

x!=0 Æ z=a Æ w’!=w’1 Æ xaw’ * ls (w’,w’1) * yaw’1

Symbolic Heaps

Separation logic formulas of the form:

(x!=0 Æ z=a Æ w’!=w’1) Æ (xaw’ * ls (w’,w’1) * yaw’1)

SH = Set of all symbolic heapsGhoSH = Set of sym. heaps with ghost vars only

Footprint Computation


t = x;

x = x->next;

free(t);

}

{ (x=aÆemp, x=aÆemp) }

{ (x=aÆls (a,0), x=0Æemp), (x=0Æemp, x=0Æemp), … }

Fixpoint Computation

2 Pfin(GhoSH, SH)

2 Pfin (GhoSH, SH)

Footprint Computation «x=x->next¬ : Pfin(GhoSH x SH) ! Pfin(GhoSH x SH)

rearr(x) : GhoSH x SH ! Pfin(GhoSH x SH)

exec(x=x->next) : GhoSH x SH ! GhoSH x SH abs : GhoSH x SH ! CanGhoSH x CanSH{ (x=aÆls a b, x=aÆls a b), (x=aÆls a b, x=bÆls a b) }

{ (x=aÆls a b, x=aÆaab), (x=aÆls a b, x=aÆaav’*ls v’ b), (x=aÆls a b*bac, x=bÆls a b*bac) }

rearr(x)(F,P) = { (F,P1), …, (F,Pn) } if SpInvRearr(x)(P) = {P1, …, Pn}= { (F*aab, P*aab) } else if P ` x=a= { (false,false) } otherwise





{ ………………………………., (x=aÆls a b*bac, x=cÆls a b*bac) }





{ ………………………………., (x=aÆls a b*bac, x=cÆls a b*bac) }{ ………………………………., (x=aÆls a b*bac, x=cÆls a c) }{ ………………………………., (x=aÆls a c*bac, x=cÆls a c) }

List Disposal

list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

x

0

List Disposal

list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

x

0

t


list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}


list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

Discovered Precondition: x=a Æ emp

x=a Æ emp

Loop: (x=aÆemp, x=aÆemp) (x=aÆa!=0Æaab, x=bÆa!=0Æt=aÆemp) (x=aÆa!=0Æls a c, x=cÆt=bÆb!=0Æemp)


list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

Discovered Precondition: x=a Æ a!=0 Æ emp

x=a Æ empx=a Æ a!=0 Æ emp



list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

Discovered Precondition: x=a Æ a!=0 Æ emp


x=a Æ a!=0 Æ t=a Æ emp



list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

Discovered Precondition: x=a Æ a!=0 Æ emp * aab


x=a Æ a!=0 Æ t=a Æ empx=b Æ a!=0 Æ t=a Æ emp * aab



list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

Discovered Precondition: x=a Æ a!=0 Æ emp * aab


x=a Æ a!=0 Æ t=a Æ emp

x=b Æ a!=0 Æ t=a Æ emp

x=b Æ a!=0 Æ t=a Æ emp * aab



list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

Discovered Precondition: x=a Æ a!=0 Æ b!=0 Æ emp * aab




x=b Æ a!=0 Æ t=a Æ b!=0 Æ emp



list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

Discovered Precondition: x=a Æ a!=0 Æ b!=0 Æ emp * aab




x=b Æ a!=0 Æ t=a Æ b!=0 Æ empx=b Æ a!=0 Æ t=b Æ b!=0 Æ emp


x=b Æ t=b Æ b!=0 Æ emp


list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

Discovered Precondition: x=a Æ a!=0 Æ b!=0 Æ emp * aab * bac




x=b Æ a!=0 Æ t=a Æ b!=0 Æ empx=b Æ t=b Æ b!=0 Æ empx=c Æ t=b Æ b!=0 Æ emp * bac

Discovered Precondition: x=a Æ a!=0 Æ b!=0 Æ emp * ls a c a




list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}






x=c Æ t=b Æ b!=0 Æ emp




list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}







Discovered Precondition: x=a Æ a!=0 Æ b!=0 Æ emp * ls a c



list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}










list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}









Result: (x=aÆa=0Æemp, x=aÆa=0Æemp) (x=aÆa!=0Æb=0Æaab, x=bÆa!=0Æt=aÆb=0Æemp) (x=aÆa!=0Æc=0Æls a c, x=cÆt=bÆb!=0Æc=0Æemp)

Shape Analysis with SpaceInvader

list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

(x=aÆa=0Æemp, x=aÆa=0Æemp)(x=aÆa!=0Æb=0Æaab, x=bÆa!=0Æt=aÆb=0Æemp)(x=aÆa!=0Æc=0Æls a c, x=cÆt=bÆb!=0Æc=0Æemp)

(x=aÆa=0Æemp, x=aÆa=0Æemp)(x=aÆa!=0Æb=0Æaab, x=bÆa!=0Æt=aÆb=0Æemp)(x=aÆa!=0Æc=0Æls a c, x=cÆt=bÆb!=0Æc=0Æemp)

{x=a’Æa’=0Æemp}

{x=a’Æa’!=0Æls a’ 0}

{x=a’Æa’!=0Æa’a0}

{ x=0 Æ emp }

{ x=0 Æ emp }

{ x=0 Æ emp }

Footprint Computation, Ideally

F

F0

D P C

«C¬ : Pfin(GhoSH x SH) ! Pfin(GhoSH x SH)

Supp. «C¬{ (F,P) } = { (G1,Q1), (G2,Q2) }.

Goal:8D, if `SL{F}D{P}, then 9Fi. G=F*Fi and `SL{F*Fi}D;C{Qi}.

QG

Footprint Computation, Ideally


Supp. «C¬{ (F,P) } = { (G1,Q1), (G2,Q2) }.


«x=x->next¬{ (t=aÆx=bÆaab, t=bÆx=bÆemp) }=

{ (t=aÆx=bÆaab*bac, t=bÆx=cÆbac) }

«x=x->next¬{ (t=aÆx=bÆaab, t=bÆx=bÆemp) }=

{ (t=aÆx=bÆls a c , t=bÆx=cÆbac) }

{t=aÆx=bÆaab*bac} …….;x=x->next{t=bÆx=cÆbac}

{t=aÆx=bÆaab} free(t);t=x {t=bÆx=bÆemp}

{t=aÆx=bÆls a c } …….;x=x->next{t=bÆx=cÆbac}

Footprint Computation, Actually


Supp. «C¬{ (F,P) } = { (G1,Q1), (G2,Q2) }.


Actually: for all D, if `SL {F}D{P}, then 9Pi,Fi. Gi¶F*Fi, `SL{F*Fi}D;C{Pi},

PiµQi.

F

Fi

D P CPi

Gi

Qi

Abstraction abs

Rearrangement rearr(E)



Supp. «C¬{ (F,P) } = { (G1,Q1), (G2,Q2) }.



PiµQi.

F

Fi

D P CPi

Gi

Qi

Abstraction abs

Rearrangement rearr(E)

But, only abs and rearr(E)!



Supp. «C¬{ (F,P) } = { (G1,Q1), (G2,Q2) }.



PiµQi.

F D P free(t)


Fi Pi

proof rule for free(t) in sep. logic



Supp. «C¬{ (F,P) } = { (G1,Q1), (G2,Q2) }.



PiµQi.

F D P free(t)


Fi PiFi

Sound because of Frame Rule in sep. log.

{F}D{P}

{F*Fi}D{P*Fi} {P*Fi}free(t){Pi}

{P*Fi}D;free(t){Pi}

proof rule for free(t) in sep. logic

Backward Footprint Computation

list t*;while (x!

=0) { t = x; x = x-

>next; free(t);}

Backward:

assert(x!=0);t = x;x = x->next;free(t);assert(x=0);

Forward:

assert(x!=0);t = x;x = x->next;free(t);assert(x=0);

Experiments with List Programs

MacBook, 2GH Intel Core 2 Duo. 2GB Mem.

…x=a Æ y=b Æ ls a 0

…

append.c

merge.c…

x=a Æ y=c Æ ls a b * ls c d

…

Experiments with Firewire

MacBook, 2GH Intel Core 2 Duo. 2GB Mem.

t1394_SetAddressData

t1394Diag_CancelIrp

t1394_GetAddressData

t1394_SetAddressDataFix

t1394Diag_CancelIrpFix

t1394_GetAddressDataFix

footprint analysis: a shape analysis that discovers preconditions

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