Get rid of registers with trash values. More...

#include <coreaction.hh>

Inheritance diagram for ActionLikelyTrash:

Public Member Functions
	ActionLikelyTrash (const string &g)
	Constructor.

virtual Action *	clone (const ActionGroupList &grouplist) const
	Clone the Action. More...

virtual int4	apply (Funcdata &data)
	Make a single attempt to apply this Action. More...

Public Member Functions inherited from Action
	Action (uint4 f, const string &nm, const string &g)
	Base constructor for an Action. More...

virtual	~Action (void)
	Destructor.

virtual void	printStatistics (ostream &s) const
	Dump statistics to stream. More...

int4	perform (Funcdata &data)
	Perform this action (if necessary) More...

bool	setBreakPoint (uint4 tp, const string &specify)
	Set a breakpoint on this action. More...

bool	setWarning (bool val, const string &specify)
	Set a warning on this action. More...

bool	disableRule (const string &specify)
	Disable a specific Rule within this. More...

bool	enableRule (const string &specify)
	Enable a specific Rule within this. More...

const string &	getName (void) const
	Get the Action's name.

const string &	getGroup (void) const
	Get the Action's group.

uint4	getStatus (void) const
	Get the current status of this Action.

uint4	getNumTests (void)
	Get the number of times apply() was invoked.

uint4	getNumApply (void)

virtual void	reset (Funcdata &data)
	Reset the Action for a new function. More...

virtual void	resetStats (void)
	Reset all the counts to zero. More...

virtual int4	print (ostream &s, int4 num, int4 depth) const
	Print a description of this Action to stream. More...

virtual void	printState (ostream &s) const
	Print status to stream. More...

virtual void	saveXml (ostream &s) const
	Save specifics of this action to stream.

virtual void	restoreXml (const Element el, Funcdata fd)
	Load specifics of action from XML.

virtual Action *	getSubAction (const string &specify)
	Retrieve a specific sub-action by name. More...

virtual Rule *	getSubRule (const string &specify)
	Retrieve a specific sub-rule by name. More...

Static Private Member Functions
static uint4	countMarks (PcodeOp *op)

static bool	traceTrash (Varnode vn, vector< PcodeOp > &indlist)
	Decide if the given Varnode only ever flows into CPUI_INDIRECT. More...

Additional Inherited Members
Public Types inherited from Action
enum	ruleflags { rule_repeatapply = 4, rule_onceperfunc = 8, rule_oneactperfunc = 16, rule_debug = 32, rule_warnings_on = 64, rule_warnings_given = 128 }
	Boolean behavior properties governing this particular Action. More...

enum	statusflags { status_start =1, status_breakstarthit =2, status_repeat =4, status_mid =8, status_end =16, status_actionbreak =32 }
	Boolean properties describing the status of an action. More...

enum	breakflags { break_start = 1, tmpbreak_start = 2, break_action = 4, tmpbreak_action = 8 }
	Break points associated with an Action. More...

Protected Member Functions inherited from Action
void	issueWarning (Architecture *glb)
	Warn that this Action has applied. More...

bool	checkStartBreak (void)
	Check start breakpoint. More...

bool	checkActionBreak (void)
	Check action breakpoint. More...

void	turnOnWarnings (void)
	Enable warnings for this Action.

void	turnOffWarnings (void)
	Disable warnings for this Action.

Protected Attributes inherited from Action
int4	lcount
	Changes not including last call to apply()

int4	count
	Number of changes made by this action so far.

uint4	status
	Current status.

uint4	breakpoint
	Breakpoint properties.

uint4	flags
	Behavior properties.

uint4	count_tests
	Number of times apply() has been called.

uint4	count_apply
	Number of times apply() made changes.

string	name
	Name of the action.

string	basegroup
	Base group this action belongs to.

Detailed Description

Get rid of registers with trash values.

Register locations called likely trash are read as a side-effect of some instruction the compiler was using. The canonical example in x86 code is the PUSH ECX which compilers use to create space on the stack without caring about what's in ECX. Even though the decompiler can see that the read ECX value is never getting used directly by the function, because the value is getting copied to the stack, the decompiler frequently can't tell if the value has been aliased across sub-function calls. By marking the ECX register as likely \ trash the decompiler will assume that, unless there is a direct read of the incoming ECX, none of subfunctions alias the stack location where ECX was stored. This allows the spurious references to the register to be removed.

Member Function Documentation

◆ apply()

int4 ActionLikelyTrash::apply ( Funcdata & data )

virtual

Make a single attempt to apply this Action.

This is the main entry point for applying changes to a function that are specific to this Action. The method can inspect whatever it wants to decide if the Action does or does not apply. Changes are indicated by incrementing the count field.

Parameters

data	is the function to inspect/modify

Returns: 0 for a complete application, -1 for a partial completion (due to breakpoint)

Implements Action.

References PcodeOp::code(), Action::count, CPUI_INDIRECT, CPUI_INT_AND, Funcdata::findCoveredInput(), Funcdata::getFuncProto(), PcodeOp::getIn(), FuncProto::getLikelyTrash(), Varnode::getSize(), Funcdata::newConstant(), FuncProto::numLikelyTrash(), Funcdata::opSetInput(), traceTrash(), and Funcdata::truncateIndirect().

◆ clone()

virtual Action* ActionLikelyTrash::clone ( const ActionGroupList & grouplist ) const

inlinevirtual

Clone the Action.

If this Action is a member of one of the groups in the grouplist, this returns a clone of the Action, otherwise NULL is returned.

Parameters

grouplist is the list of groups being cloned

Returns: the cloned Action or NULL

Implements Action.

References ActionLikelyTrash(), ActionGroupList::contains(), and Action::getGroup().

◆ countMarks()

uint4 ActionLikelyTrash::countMarks ( PcodeOp * op )

staticprivate

Count the number of inputs to op which have their mark set

Parameters

op	is the PcodeOp to count

Returns: the number of marks set

References PcodeOp::code(), CPUI_INDIRECT, Varnode::getDef(), PcodeOp::getIn(), Varnode::isMark(), Varnode::isWritten(), and PcodeOp::numInput().

Referenced by traceTrash().

◆ traceTrash()

bool ActionLikelyTrash::traceTrash	(	Varnode *	vn,
		vector< PcodeOp * > &	indlist
	)

staticprivate

Decide if the given Varnode only ever flows into CPUI_INDIRECT.

Return all the CPUI_INDIRECT ops that the Varnode hits in a list. Trace forward down all paths from -vn-, if we hit

CPUI_INDIRECT -> trim that path and store that op in the resulting -indlist-
CPUI_SUBPIECE
CPUI_MULTIEQUAL
CPUI_PIECE
CPUI_AND -> follow through to output
anything else -> consider -vn- to NOT be trash

For any CPUI_MULTIEQUAL and CPUI_PIECE that are hit, all the other inputs must be hit as well

Parameters

vn	is the given Varnode
indlist	is the list to populate with CPUI_INDIRECT ops

Returns: true if all flows look like trash

References Varnode::beginDescend(), calc_mask(), PcodeOp::code(), countMarks(), CPUI_INDIRECT, CPUI_INT_AND, CPUI_MULTIEQUAL, CPUI_PIECE, CPUI_SUBPIECE, Varnode::endDescend(), PcodeOp::getIn(), Varnode::getOffset(), PcodeOp::getOut(), Varnode::getSize(), Varnode::isConstant(), PcodeOp::isMark(), Varnode::isMark(), Varnode::isPersist(), PcodeOp::numInput(), PcodeOp::setMark(), and Varnode::setMark().

Referenced by apply().

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

coreaction.hh
coreaction.cc

Public Member Functions

Static Private Member Functions

Additional Inherited Members

Detailed Description

Member Function Documentation

◆ apply()

◆ clone()

◆ countMarks()

◆ traceTrash()