< Clearing the map at the end of a function is a start, but you ought to make
sure you don't clear it for the function that called this one. I suppose that's
a refinement that can be made later, since it only produces false negatives.
(I'm not super happy about not being able to merge branches within the
<function, though.)
No I don't like it either and would like to fix it but I haven't figured out
how. Can I find out the current function somehow when the division occurs?
< +unsigned DivZeroChecker2::getBlockID(const Expr *B, CheckerContext &C) const
{
< + const CFG &cfg = C.getPredecessor()->getCFG();
< + for (CFG::const_iterator I = cfg.begin(); I != cfg.end(); ++I) {
< + for (CFGBlock::const_iterator BI = (*I)->begin(), BE = (*I)->end();
< + BI != BE; ++BI) {
< + Optional<CFGStmt> stmt = BI->getAs<CFGStmt>();
< + if (stmt && stmt->getStmt() == B)
< + return (*I)->getBlockID();
< + }
< + }
< + return 0;
< +}
< This is much too expensive. The CheckerContext has a NodeBuilder, which has a
NodeBuilderContext, which has a CFGBlock. We should just expose that somewhere
(probably on CheckerContext).
I have made a get function in CheckerContext to retrieve the NodeBuilder. Is
there something better than blockid? Scope id would have been nice. Blockid
creates false negatives like below when an if-statement that has nothing to do
with the division comes in between.
void err_not(int x, int y) {
var = 77 / x;
if (y)
int v = 0;
if (!x){}// should warn here but don't since this is a new blockid.
}
< Finally, please include some test cases with inlining so that the
clear-at-end-of-function logic is exercised.
What's the difference with inline and normal functions in this case? As I have
understood it inline functions are still treated like normal functions when
walking the ast.
< Thanks for working on this, and sorry for the slow responses.
< Jordan
It's ok I'm not that fast either.
On Apr 24, 2014, at 7:50 , Anders Rönnholm
<anders.ronnh...@evidente.se<mailto:anders.ronnh...@evidente.se>> wrote:
Hi Jordan,
I have changed the patch to store $foo instead of the variable. I also make
sure that the divison and check is in the same block by comparing the blockid.
This handles your second example.
//Anders
________________________________________
Från: Jordan Rose [jordan_r...@apple.com<mailto:jordan_r...@apple.com>]
Skickat: den 5 april 2014 04:03
Till: Anders Rönnholm
Cc: cfe-commits@cs.uiuc.edu<mailto:cfe-commits@cs.uiuc.edu>; Daniel Marjamäki
Ämne: Re: [PATCH] Division by zero
On Apr 3, 2014, at 7:18 , Anders Rönnholm
<anders.ronnh...@evidente.se<mailto:anders.ronnh...@evidente.se><mailto:anders.ronnh...@evidente.se>>
wrote:
Hi Jordan, see below for comments and questions.
< Hi, Anders. I have some high-level concerns about this checker as it's
structured now. First (and most mundanely), the checker is conflating values
and locations. A particular symbol in the analyzer can <never change, so
there's no reason to ever have to remove something from the DivZeroMap because
of invalidation.
<
< int x = foo(); // The value stored in 'x' is some symbol '$foo'
< int y = 5 / x; // use $foo
< x = bar(); // The value stored in 'x' is now some symbol '$bar', but '$foo'
hasn't changed.
< On the flip side, I'm concerned that values never leave the map. You could
clean up some of them with a checkDeadSymbols callback, but that's still a
large amount of state for values that may have been < checked quite a while
ago. In particular, this will result in false positives if a value is used in
one function and then checked in another.
Why don't we have to remove it? When x changes as you say we need to remove it
or flag it so we don't check x against zero anymore since x has changed after
the division.
I guess we could remove all items in DivZeroMap when we leave the function, do
you think that would work?
"When 'x' changes" is the interesting part. '$foo' can't change, and that's
what you're inserting into the map. The value stored in 'x' can change, and
that's why 'x' is being removed from the map. But 'x' should never be in the
map in the first place; it's '$foo', the value, that's important.
Here's another example:
int x = foo();
int y = x;
use(5 / x);
if (y == 0) // warn!
If we track the variable 'x', then we won't catch this case, even though it's
pretty much equivalent to what you had before.
Here's another problem with doing things this way: doing this as a
path-sensitive check says that there's a spurious comparison along one path,
but you really need to know if it happens along all paths:
void foo() {
bool isPositive;
int x = getValue(&isPositive);
if (isPositive) {
use(5 / x);
}
if (x == 0) {
log("x is zero");
}
}
In this case, there exists a path where 'x' checked against 0 after being used
as a denominator, but it's not actually a problem. You can argue that the test
should be moved up before the use, or that an assertion should be added, but I
don't know if we want to tackle that. OTOH, you would have to add an assertion
if you did move the test before the use.
I like the idea of clearing the map/set on function exit, because it's somewhat
reasonable to add asserts within a function...but you'd basically also have to
clear it on function entrance too. Which means you have one set per
LocationContext. I haven't fully thought that through yet.
<
< (The opposite order hit us so much when dealing with C++ support that we
coined a term for it: "inlined defensive checks". This occurs when one function
accepts null pointers and so does a check, the <caller knows the value is
never null but doesn't actually assert it, and then the value is used. We ended
up having to silence all bugs where the first null check came from an inlined
function, which <definitely through out some true positives with the false
ones.)
<
< What do you think?
< Jordan
<
< P.S. If your map entries always map to "true", you might as well use a set.
;-)
Is it possible to get a specific entry using set or do you have to iterate
through all items to find the one your looking for?
With map you can do this,:
const bool D = State->get<DivZeroMap>(MR);
but with set i'm only able to get them all.
DivZeroMapTy DivZeroes = State->get<DivZeroMap>();
For future reference, set traits get a State->contains<DivZeroMap>().
Jordan
<divzero2.diff>
Index: include/clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h
===================================================================
--- include/clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h (revision 207117)
+++ include/clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h (working copy)
@@ -174,6 +174,8 @@
return Pred->getLocationContext()->getAnalysisDeclContext();
}
+ NodeBuilder &getNodeBuilder() { return NB; }
+
/// \brief If the given node corresponds to a PostStore program point, retrieve
/// the location region as it was uttered in the code.
///
Index: lib/StaticAnalyzer/Checkers/Checkers.td
===================================================================
--- lib/StaticAnalyzer/Checkers/Checkers.td (revision 207117)
+++ lib/StaticAnalyzer/Checkers/Checkers.td (working copy)
@@ -72,6 +72,10 @@
HelpText<"Check for division by zero">,
DescFile<"DivZeroChecker.cpp">;
+def DivZeroChecker2 : Checker<"DivideZero2">,
+ HelpText<"Check for division by variable that is later compared against 0. Either the comparison is useless or there is division by zero.">,
+ DescFile<"DivZeroChecker2.cpp">;
+
def UndefResultChecker : Checker<"UndefinedBinaryOperatorResult">,
HelpText<"Check for undefined results of binary operators">,
DescFile<"UndefResultChecker.cpp">;
Index: lib/StaticAnalyzer/Checkers/CMakeLists.txt
===================================================================
--- lib/StaticAnalyzer/Checkers/CMakeLists.txt (revision 207117)
+++ lib/StaticAnalyzer/Checkers/CMakeLists.txt (working copy)
@@ -32,6 +32,7 @@
DereferenceChecker.cpp
DirectIvarAssignment.cpp
DivZeroChecker.cpp
+ DivZeroChecker2.cpp
DynamicTypePropagation.cpp
ExprInspectionChecker.cpp
FixedAddressChecker.cpp
Index: lib/StaticAnalyzer/Checkers/DivZeroChecker2.cpp
===================================================================
--- lib/StaticAnalyzer/Checkers/DivZeroChecker2.cpp (revision 0)
+++ lib/StaticAnalyzer/Checkers/DivZeroChecker2.cpp (revision 0)
@@ -0,0 +1,217 @@
+//== DivZeroChecker2.cpp - Division by zero checker -------------*- C++ -*--==//
+//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This defines DivZeroChecker2, a builtin check that performs checks for
+// division by zero where the division occurs before comparison with zero.
+//
+//===----------------------------------------------------------------------===//
+
+#include "ClangSACheckers.h"
+#include "clang/StaticAnalyzer/Core/BugReporter/BugType.h"
+#include "clang/StaticAnalyzer/Core/Checker.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CallEvent.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+
+using namespace clang;
+using namespace ento;
+
+namespace {
+
+class DivisionBRVisitor : public BugReporterVisitorImpl<DivisionBRVisitor> {
+protected:
+ SVal V;
+ bool Satisfied;
+
+public:
+ DivisionBRVisitor(KnownSVal V) : V(V), Satisfied(false) {}
+
+ void Profile(llvm::FoldingSetNodeID &ID) const override { ID.Add(V); }
+
+ PathDiagnosticPiece *VisitNode(const ExplodedNode *Succ,
+ const ExplodedNode *Pred,
+ BugReporterContext &BRC,
+ BugReport &BR) override;
+};
+
+class DivZeroChecker2
+ : public Checker<check::PreStmt<BinaryOperator>, check::BranchCondition,
+ check::EndFunction> {
+ mutable std::unique_ptr<BuiltinBug> BB;
+ void reportBug(StringRef Msg, SVal Val, CheckerContext &C) const;
+
+public:
+ void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
+ void checkBranchCondition(const Stmt *Condition, CheckerContext &C) const;
+ void checkEndFunction(CheckerContext &C) const;
+ void setDivZeroMap(SVal Var, unsigned DS, CheckerContext &C) const;
+ bool hasDivZeroMapSval(SVal Var, unsigned Block,
+ const CheckerContext &C) const;
+ unsigned getBlockID(CheckerContext &C) const;
+};
+} // end anonymous namespace
+
+REGISTER_MAP_WITH_PROGRAMSTATE(DivZeroMap, SymbolRef, unsigned)
+
+PathDiagnosticPiece *DivisionBRVisitor::VisitNode(const ExplodedNode *Succ,
+ const ExplodedNode *Pred,
+ BugReporterContext &BRC,
+ BugReport &BR) {
+ if (Satisfied)
+ return NULL;
+
+ const Expr *E = 0;
+
+ if (Optional<PostStmt> P = Succ->getLocationAs<PostStmt>())
+ if (const BinaryOperator *BO = P->getStmtAs<BinaryOperator>()) {
+ BinaryOperator::Opcode Op = BO->getOpcode();
+ if (Op == BO_Div || Op == BO_Rem || Op == BO_DivAssign ||
+ Op == BO_RemAssign) {
+ E = BO->getRHS();
+ }
+ }
+
+ if (!E)
+ return NULL;
+
+ ProgramStateRef State = Succ->getState();
+ SVal VV = State->getSVal(E, Succ->getLocationContext());
+ if (V == VV) {
+ Satisfied = true;
+
+ // Construct a new PathDiagnosticPiece.
+ ProgramPoint P = Succ->getLocation();
+ PathDiagnosticLocation L = PathDiagnosticLocation::create(P, BRC.getSourceManager());
+
+ if (!L.isValid() || !L.asLocation().isValid())
+ return NULL;
+
+ return new PathDiagnosticEventPiece(L, "Division with compared value made here");
+ }
+
+ return NULL;
+}
+
+void DivZeroChecker2::setDivZeroMap(SVal Var, unsigned BlockId,
+ CheckerContext &C) const {
+ SymbolRef SR = Var.getAsSymbol();
+ if (!SR)
+ return;
+
+ ProgramStateRef State = C.getState();
+ State = State->set<DivZeroMap>(SR, BlockId);
+ C.addTransition(State);
+}
+
+bool DivZeroChecker2::hasDivZeroMapSval(SVal Var, unsigned BlockId,
+ const CheckerContext &C) const {
+ SymbolRef SR = Var.getAsSymbol();
+ if (!SR)
+ return false;
+
+ const unsigned *MapBlockId = C.getState()->get<DivZeroMap>(SR);
+ return (MapBlockId && *MapBlockId == BlockId);
+}
+
+unsigned DivZeroChecker2::getBlockID(CheckerContext &C) const {
+ return C.getNodeBuilder().getContext().getBlock()->getBlockID();
+}
+
+void DivZeroChecker2::reportBug(StringRef Msg, SVal Val,
+ CheckerContext &C) const {
+ if (ExplodedNode *N = C.generateSink(C.getState())) {
+ if (!BB)
+ BB.reset(new BuiltinBug(this, "Division by zero"));
+
+ if (Optional<KnownSVal> V = Val.getAs<KnownSVal>()) {
+ BugReport *R = new BugReport(*BB, Msg, N);
+
+ R->addVisitor(new DivisionBRVisitor(*V));
+ C.emitReport(R);
+ }
+ }
+}
+
+void DivZeroChecker2::checkEndFunction(CheckerContext &C) const {
+ ProgramStateRef State = C.getState();
+ State = State->remove<DivZeroMap>();
+ C.addTransition(State);
+}
+
+void DivZeroChecker2::checkPreStmt(const BinaryOperator *B,
+ CheckerContext &C) const {
+ BinaryOperator::Opcode Op = B->getOpcode();
+ if (Op == BO_Div || Op == BO_Rem || Op == BO_DivAssign ||
+ Op == BO_RemAssign) {
+ if (!B->getRHS()->getType()->isScalarType())
+ return;
+
+ ProgramStateRef State = C.getState();
+ SVal Val = C.getSVal(B->getRHS());
+ Optional<DefinedSVal> DSV = Val.getAs<DefinedSVal>();
+
+ if (!DSV)
+ return;
+
+ // Make sure SVal can be zero.
+ if (!C.getConstraintManager().assume(State, *DSV, false))
+ return;
+
+ setDivZeroMap(Val, getBlockID(C), C);
+ }
+}
+
+void DivZeroChecker2::checkBranchCondition(const Stmt *Condition,
+ CheckerContext &C) const {
+ if (const BinaryOperator *B = dyn_cast<BinaryOperator>(Condition)) {
+ if (B->isComparisonOp()) {
+ const IntegerLiteral *IntLiteral = dyn_cast<IntegerLiteral>(B->getRHS());
+ bool LRHS = true;
+ if (!IntLiteral) {
+ IntLiteral = dyn_cast<IntegerLiteral>(B->getLHS());
+ LRHS = false;
+ }
+
+ if (!IntLiteral || IntLiteral->getValue() != 0)
+ return;
+
+ SVal Val = C.getSVal(LRHS ? B->getLHS() : B->getRHS());
+ if (hasDivZeroMapSval(Val, getBlockID(C), C))
+ reportBug("Value being compared against zero has already been used for "
+ "division",
+ Val, C);
+ }
+ } else if (const UnaryOperator *U = dyn_cast<UnaryOperator>(Condition)) {
+ if (U->getOpcode() == UO_LNot) {
+ SVal Val, Val2;
+ if (const ImplicitCastExpr *I =
+ dyn_cast<ImplicitCastExpr>(U->getSubExpr()))
+ Val = C.getSVal(I->getSubExpr());
+ else
+ Val = C.getSVal(U->getSubExpr());
+
+ if (hasDivZeroMapSval(Val, getBlockID(C), C))
+ reportBug("Value being compared against zero has already been used for "
+ "division",
+ Val, C);
+ }
+ } else if (const ImplicitCastExpr *IE =
+ dyn_cast<ImplicitCastExpr>(Condition)) {
+
+ SVal Val = C.getSVal(IE->getSubExpr());
+
+ if (hasDivZeroMapSval(Val, getBlockID(C), C))
+ reportBug("Value being compared against zero has already been used for "
+ "division",
+ Val, C);
+ }
+}
+
+void ento::registerDivZeroChecker2(CheckerManager &mgr) {
+ mgr.registerChecker<DivZeroChecker2>();
+}
Index: test/Analysis/div-zero2.cpp
===================================================================
--- test/Analysis/div-zero2.cpp (revision 0)
+++ test/Analysis/div-zero2.cpp (revision 0)
@@ -0,0 +1,161 @@
+// RUN: %clang_cc1 -analyze -analyzer-checker=core.DivideZero2 -analyzer-output=text -verify %s
+
+int var;
+
+void err_eq(int x) {
+ var = 77 / x; // expected-note {{Division with compared value made here}}
+ if (x==0){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+
+void err_eq2(int x) {
+ var = 77 / x; // expected-note {{Division with compared value made here}}
+ if (0==x){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+
+void err_ne(int x) {
+ var = 77 / x; // expected-note {{Division with compared value made here}}
+ if (x!=0){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+
+void err_ge(int x) {
+ var = 77 / x; // expected-note {{Division with compared value made here}}
+ if (x>=0){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+
+void err_le(int x) {
+ var = 77 / x; // expected-note {{Division with compared value made here}}
+ if (x<=0){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+
+void err_yes(int x) {
+ var = 77 / x; // expected-note {{Division with compared value made here}}
+ if (x){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+void err_not(int x) {
+ var = 77 / x; // expected-note {{Division with compared value made here}}
+ if (!x){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+
+void err_pnot(int x) {
+ int *y = &x;
+ var = 77 / *y; // expected-note {{Division with compared value made here}}
+ if (!x){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+
+void err_pnot2(int x) {
+ int *y = &x;
+ var = 77 / x; // expected-note {{Division with compared value made here}}
+ if (!*y){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+
+void err_ppnot(int x) {
+ int *y = &x;
+ int **z = &y;
+ var = 77 / **z; // expected-note {{Division with compared value made here}}
+ if (!x){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+
+void ok_other(int x, int y) {
+ var = 77 / y;
+ if (x == 0){}
+}
+
+void ok_assign(int x) {
+ var = 77 / x;
+ x = var / 77; // <- assignment => don't warn
+ if (x == 0){}
+}
+
+void ok_assign2(int x) {
+ var = 77 / x;
+ x = var / 77; // <- assignment => don't warn
+ if (0 == x){}
+}
+
+void ok_dec(int x) {
+ var = 77 / x;
+ x--; // <- assignment => don't warn
+ if (x == 0){}
+}
+
+void ok_inc(int x) {
+ var = 77 / x;
+ x++; // <- assignment => don't warn
+ if (x == 0){}
+}
+
+void do_something_ptr(int*x);
+void ok_callfunc_ptr(int x) {
+ var = 77 / x;
+ do_something_ptr(&x); // <- pass address of x to function => don't warn
+ if (x == 0){}
+}
+
+void do_something_ref(int&x);
+void ok_callfunc_ref(int x) {
+ var = 77 / x;
+ do_something_ref(x); // <- pass reference of x to function => don't warn
+ if (x == 0){}
+}
+
+void do_something(int x);
+void nok_callfunc(int x) {
+ var = 77 / x; // expected-note {{Division with compared value made here}}
+ do_something(x);
+ if (x == 0){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+void ok_if(int x) {
+ if (x > 3)
+ var = 77 / x;
+ if (x == 0){}
+}
+
+void ok_if2(int x) {
+ if (x < 3)
+ var = 77 / x;
+ if (x == 0){} // TODO warn here
+}
+
+void ok_pif(int x) {
+ int *y = &x;
+ if (x < 3)
+ var = 77 / *y;
+ if (x == 0){} // TODO warn here
+}
+
+int getValue(bool *isPositive);
+void use(int a);
+void foo() {
+ bool isPositive;
+ int x = getValue(&isPositive);
+ if (isPositive) {
+ use(5 / x);
+ }
+
+ if (x == 0) {}
+}
+
+int getValue2();
+void foo2() {
+ int x = getValue2();
+ int y = x;
+
+ use(5 / x); // expected-note {{Division with compared value made here}}
+ if (y == 0){} // expected-warning {{Value being compared against zero has already been used for division}}
+} // expected-note@-1 {{Value being compared against zero has already been used for division}}
+
+void ok_while(int x) {
+ int n = 100 / x;
+ while (x != 0) { // <- do not warn
+ x--;
+ }
+}
+
+void err_not(int x, int y) {
+ var = 77 / x;
+
+ if (y)
+ int v = 0;
+
+ if (!x){} // TODO warn here
+}
_______________________________________________
cfe-commits mailing list
cfe-commits@cs.uiuc.edu
http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
