AliasChecker Class Reference

A light-weight class for analyzing pointers and aliasing on the stack. More...

#include <varmap.hh>

Classes
struct	AddBase
	A helper class holding a Varnode pointer reference and a possible index added to it. More...

Public Member Functions
	AliasChecker ()
	Constructor.
void	gather (const Funcdata *f, AddrSpace *spc, bool defer)
	Gather Varnodes that point on the stack. More...
bool	hasLocalAlias (Varnode *vn) const
	Return true if it looks like the given Varnode is aliased by a pointer. More...
void	sortAlias (void) const
	Sort the alias starting offsets.
const vector< AddBase > &	getAddBase (void) const
	Get the collection of pointer Varnodes.
const vector< uintb > &	getAlias (void) const
	Get the list of alias starting offsets.

Static Public Member Functions
static void	gatherAdditiveBase (Varnode *startvn, vector< AddBase > &addbase)
	Gather result Varnodes for all sums that the given starting Varnode is involved in. More...
static uintb	gatherOffset (Varnode *vn)
	If the given Varnode is a sum result, return the constant portion of this sum. More...

Private Member Functions
void	deriveBoundaries (const FuncProto &proto)
	Set up basic boundaries for the stack layout. More...
void	gatherInternal (void) const
	Run through Varnodes looking for pointers into the stack. More...

Private Attributes
const Funcdata *	fd
	Function being searched for aliases.
AddrSpace *	space
	AddressSpace in which to search.
vector< AddBase >	addBase
	Collection of pointers into the AddressSpace.
vector< uintb >	alias
	List of aliased addresses (as offsets)
bool	calculated
	Have aliases been calculated.
uintb	localExtreme
	Largest possible offset for a local variable.
uintb	localBoundary
	Boundary offset separating locals and parameters.
uintb	aliasBoundary
	Shallowest alias.
int4	direction
	1=stack grows negative, -1=positive

Detailed Description

A light-weight class for analyzing pointers and aliasing on the stack.

The gather() method looks for pointer references into a specific AddressSpace (usually the stack). Then hasLocalAlias() checks if a specific Varnode within the AddressSpace is (possibly) aliased by one of the gathered pointer references.

Member Function Documentation

void AliasChecker::deriveBoundaries ( const FuncProto &  proto )

private

Set up basic boundaries for the stack layout.

Set up basic offset boundaries for what constitutes a local variable or a parameter on the stack. This can be informed by the ProtoModel if available.

Parameters

proto

is the function prototype to use as a prototype model

References Range::getLast(), FuncProto::getLocalRange(), FuncProto::getParamRange(), and FuncProto::hasModel().

void AliasChecker::gather	(	const Funcdata *	f,
		AddrSpace *	spc,
		bool	defer
	)

Gather Varnodes that point on the stack.

For the given function and address space, gather all Varnodes that are pointers into the address space. The actual calculation can be deferred until the first time hasLocalAlias() is called.

Parameters

f	is the given function
spc	is the given address space
defer	is true is gathering is deferred

References Scope::fd, Funcdata::getFuncProto(), ScopeLocal::space, and AddrSpace::stackGrowsNegative().

Referenced by ActionActiveParam::apply(), and MapState::gatherOpen().

void AliasChecker::gatherAdditiveBase ( Varnode *  startvn, vector< AddBase > &  addbase  )

static

Gather result Varnodes for all sums that the given starting Varnode is involved in.

For every sum that involves startvn, collect the final result Varnode of the sum. A sum is any expression involving only the additive operators INT_ADD, INT_SUB, PTRADD, PTRSUB, and SEGMENTOP. The routine traverses forward recursively through all descendants of vn that are additive operations and collects all the roots of the traversed trees.

Parameters

startvn	is the Varnode to trace
addbase	will contain all the collected roots

References Varnode::beginDescend(), PcodeOp::code(), CPUI_COPY, CPUI_INT_ADD, CPUI_INT_SUB, CPUI_PTRADD, CPUI_PTRSUB, CPUI_SEGMENTOP, Varnode::endDescend(), PcodeOp::getIn(), PcodeOp::getOut(), Varnode::isConstant(), Varnode::isMark(), and Varnode::setMark().

void AliasChecker::gatherInternal ( void  ) const

private

Run through Varnodes looking for pointers into the stack.

If there is an AddrSpace (stack) pointer, find its input Varnode, and look for additive uses of it. Once all these Varnodes are accumulated, calculate specific offsets that start a region being aliased.

References AddrSpace::addressToByte(), Scope::fd, Funcdata::findSpacebaseInput(), AddrSpace::getWordSize(), and ScopeLocal::space.

uintb AliasChecker::gatherOffset ( Varnode *  vn )

static

If the given Varnode is a sum result, return the constant portion of this sum.

Treat vn as the result of a series of ADD operations. Examine all the constant terms of this sum and add them together by traversing the syntax tree rooted at vn, backwards, only through additive operations.

Parameters

vn	is the given Varnode to gather off of

Returns

the resulting sub-sum

References calc_mask(), PcodeOp::code(), CPUI_COPY, CPUI_INT_ADD, CPUI_INT_SUB, CPUI_PTRADD, CPUI_PTRSUB, CPUI_SEGMENTOP, Varnode::getDef(), PcodeOp::getIn(), Varnode::getOffset(), Varnode::getSize(), and Varnode::isConstant().

bool AliasChecker::hasLocalAlias

(

Varnode *

vn

)

const

Return true if it looks like the given Varnode is aliased by a pointer.

This is gives a rough analysis of whether the given Varnode might be aliased by another pointer in the function. If false is returned, the Varnode is not likely to have an alias. If true is returned, the Varnode might have an alias.

Parameters

vn	is the given Varnode

Returns

true if the Varnode might have a pointer alias

References Varnode::getOffset(), Varnode::getSpace(), and ScopeLocal::space.

Referenced by FuncCallSpecs::checkInputTrialUse().

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The documentation for this class was generated from the following files:

• varmap.hh
• varmap.cc