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[analyzer] Support determining origins in a conditional operator in WebKit checkers. #91143

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Merged
merged 1 commit into from
May 10, 2024
Merged

[analyzer] Support determining origins in a conditional operator in WebKit checkers. #91143

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23 changes: 15 additions & 8 deletions clang/lib/StaticAnalyzer/Checkers/WebKit/ASTUtils.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -16,8 +16,9 @@

namespace clang {

std::pair<const Expr *, bool>
tryToFindPtrOrigin(const Expr *E, bool StopAtFirstRefCountedObj) {
bool tryToFindPtrOrigin(
const Expr *E, bool StopAtFirstRefCountedObj,
std::function<bool(const clang::Expr *, bool)> callback) {
while (E) {
if (auto *tempExpr = dyn_cast<MaterializeTemporaryExpr>(E)) {
E = tempExpr->getSubExpr();
Expand All @@ -31,12 +32,18 @@ tryToFindPtrOrigin(const Expr *E, bool StopAtFirstRefCountedObj) {
E = tempExpr->getSubExpr();
continue;
}
if (auto *Expr = dyn_cast<ConditionalOperator>(E)) {
return tryToFindPtrOrigin(Expr->getTrueExpr(), StopAtFirstRefCountedObj,
callback) &&
tryToFindPtrOrigin(Expr->getFalseExpr(), StopAtFirstRefCountedObj,
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Hmm does this code play well with StopAtFirstRefCountedObj? Am I reading this right that both branches need to originate from a smart pointer, so we should never really stop in the middle between the branches?

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So the model is that we'd recurse for each expression. We'd stop at the first appearance of Ref/RefPtr if StopAtFirstRefCountedObj is set. Whether that semantics is correct or not depends on the context in which this function is called / used.

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Aha makes sense then!

callback);
}
if (auto *cast = dyn_cast<CastExpr>(E)) {
if (StopAtFirstRefCountedObj) {
if (auto *ConversionFunc =
dyn_cast_or_null<FunctionDecl>(cast->getConversionFunction())) {
if (isCtorOfRefCounted(ConversionFunc))
return {E, true};
return callback(E, true);
}
}
// FIXME: This can give false "origin" that would lead to false negatives
Expand All @@ -51,7 +58,7 @@ tryToFindPtrOrigin(const Expr *E, bool StopAtFirstRefCountedObj) {
if (IsGetterOfRefCt && *IsGetterOfRefCt) {
E = memberCall->getImplicitObjectArgument();
if (StopAtFirstRefCountedObj) {
return {E, true};
return callback(E, true);
}
continue;
}
Expand All @@ -68,17 +75,17 @@ tryToFindPtrOrigin(const Expr *E, bool StopAtFirstRefCountedObj) {
if (auto *callee = call->getDirectCallee()) {
if (isCtorOfRefCounted(callee)) {
if (StopAtFirstRefCountedObj)
return {E, true};
return callback(E, true);

E = call->getArg(0);
continue;
}

if (isReturnValueRefCounted(callee))
return {E, true};
return callback(E, true);

if (isSingleton(callee))
return {E, true};
return callback(E, true);

if (isPtrConversion(callee)) {
E = call->getArg(0);
Expand All @@ -95,7 +102,7 @@ tryToFindPtrOrigin(const Expr *E, bool StopAtFirstRefCountedObj) {
break;
}
// Some other expression.
return {E, false};
return callback(E, false);
}

bool isASafeCallArg(const Expr *E) {
Expand Down
11 changes: 7 additions & 4 deletions clang/lib/StaticAnalyzer/Checkers/WebKit/ASTUtils.h
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Expand Up @@ -13,6 +13,7 @@
#include "llvm/ADT/APInt.h"
#include "llvm/Support/Casting.h"

#include <functional>
#include <string>
#include <utility>

Expand Down Expand Up @@ -48,10 +49,12 @@ class Expr;
/// represents ref-counted object during the traversal we return relevant
/// sub-expression and true.
///
/// \returns subexpression that we traversed to and if \p
/// StopAtFirstRefCountedObj is true we also return whether we stopped early.
std::pair<const clang::Expr *, bool>
tryToFindPtrOrigin(const clang::Expr *E, bool StopAtFirstRefCountedObj);
/// Calls \p callback with the subexpression that we traversed to and if \p
/// StopAtFirstRefCountedObj is true we also specify whether we stopped early.
/// Returns false if any of calls to callbacks returned false. Otherwise true.
bool tryToFindPtrOrigin(
const clang::Expr *E, bool StopAtFirstRefCountedObj,
std::function<bool(const clang::Expr *, bool)> callback);

/// For \p E referring to a ref-countable/-counted pointer/reference we return
/// whether it's a safe call argument. Examples: function parameter or
Expand Down
36 changes: 17 additions & 19 deletions clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedCallArgsChecker.cpp
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Expand Up @@ -126,25 +126,23 @@ class UncountedCallArgsChecker
}

bool isPtrOriginSafe(const Expr *Arg) const {
std::pair<const clang::Expr *, bool> ArgOrigin =
tryToFindPtrOrigin(Arg, true);

// Temporary ref-counted object created as part of the call argument
// would outlive the call.
if (ArgOrigin.second)
return true;

if (isa<CXXNullPtrLiteralExpr>(ArgOrigin.first)) {
// foo(nullptr)
return true;
}
if (isa<IntegerLiteral>(ArgOrigin.first)) {
// FIXME: Check the value.
// foo(NULL)
return true;
}

return isASafeCallArg(ArgOrigin.first);
return tryToFindPtrOrigin(Arg, /*StopAtFirstRefCountedObj=*/true,
[](const clang::Expr *ArgOrigin, bool IsSafe) {
if (IsSafe)
return true;
if (isa<CXXNullPtrLiteralExpr>(ArgOrigin)) {
// foo(nullptr)
return true;
}
if (isa<IntegerLiteral>(ArgOrigin)) {
// FIXME: Check the value.
// foo(NULL)
return true;
}
if (isASafeCallArg(ArgOrigin))
return true;
return false;
});
}

bool shouldSkipCall(const CallExpr *CE) const {
Expand Down
73 changes: 42 additions & 31 deletions clang/lib/StaticAnalyzer/Checkers/WebKit/UncountedLocalVarsChecker.cpp
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Expand Up @@ -188,39 +188,50 @@ class UncountedLocalVarsChecker
if (!InitExpr)
return; // FIXME: later on we might warn on uninitialized vars too

const clang::Expr *const InitArgOrigin =
tryToFindPtrOrigin(InitExpr, /*StopAtFirstRefCountedObj=*/false)
.first;
if (!InitArgOrigin)
if (tryToFindPtrOrigin(
InitExpr, /*StopAtFirstRefCountedObj=*/false,
[&](const clang::Expr *InitArgOrigin, bool IsSafe) {
if (!InitArgOrigin)
return true;

if (isa<CXXThisExpr>(InitArgOrigin))
return true;

if (isa<CXXNullPtrLiteralExpr>(InitArgOrigin))
return true;

if (isa<IntegerLiteral>(InitArgOrigin))
return true;

if (auto *Ref = llvm::dyn_cast<DeclRefExpr>(InitArgOrigin)) {
if (auto *MaybeGuardian =
dyn_cast_or_null<VarDecl>(Ref->getFoundDecl())) {
const auto *MaybeGuardianArgType =
MaybeGuardian->getType().getTypePtr();
if (MaybeGuardianArgType) {
const CXXRecordDecl *const MaybeGuardianArgCXXRecord =
MaybeGuardianArgType->getAsCXXRecordDecl();
if (MaybeGuardianArgCXXRecord) {
if (MaybeGuardian->isLocalVarDecl() &&
(isRefCounted(MaybeGuardianArgCXXRecord) ||
isRefcountedStringsHack(MaybeGuardian)) &&
isGuardedScopeEmbeddedInGuardianScope(
V, MaybeGuardian))
return true;
}
}

// Parameters are guaranteed to be safe for the duration of
// the call by another checker.
if (isa<ParmVarDecl>(MaybeGuardian))
return true;
}
}

return false;
}))
return;

if (isa<CXXThisExpr>(InitArgOrigin))
return;

if (auto *Ref = llvm::dyn_cast<DeclRefExpr>(InitArgOrigin)) {
if (auto *MaybeGuardian =
dyn_cast_or_null<VarDecl>(Ref->getFoundDecl())) {
const auto *MaybeGuardianArgType =
MaybeGuardian->getType().getTypePtr();
if (MaybeGuardianArgType) {
const CXXRecordDecl *const MaybeGuardianArgCXXRecord =
MaybeGuardianArgType->getAsCXXRecordDecl();
if (MaybeGuardianArgCXXRecord) {
if (MaybeGuardian->isLocalVarDecl() &&
(isRefCounted(MaybeGuardianArgCXXRecord) ||
isRefcountedStringsHack(MaybeGuardian)) &&
isGuardedScopeEmbeddedInGuardianScope(V, MaybeGuardian))
return;
}
}

// Parameters are guaranteed to be safe for the duration of the call
// by another checker.
if (isa<ParmVarDecl>(MaybeGuardian))
return;
}
}

reportBug(V);
}
}
Expand Down
14 changes: 14 additions & 0 deletions clang/test/Analysis/Checkers/WebKit/call-args.cpp
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Expand Up @@ -344,3 +344,17 @@ namespace cxx_member_operator_call {
// expected-warning@-1{{Call argument for parameter 'bad' is uncounted and unsafe}}
}
}

namespace call_with_ptr_on_ref {
Ref<RefCountable> provideProtected();
void bar(RefCountable* bad);
bool baz();
void foo(bool v) {
bar(v ? nullptr : provideProtected().ptr());
bar(baz() ? provideProtected().ptr() : nullptr);
bar(v ? provide() : provideProtected().ptr());
// expected-warning@-1{{Call argument for parameter 'bad' is uncounted and unsafe}}
bar(v ? provideProtected().ptr() : provide());
// expected-warning@-1{{Call argument for parameter 'bad' is uncounted and unsafe}}
}
}
18 changes: 18 additions & 0 deletions clang/test/Analysis/Checkers/WebKit/uncounted-local-vars.cpp
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Expand Up @@ -198,3 +198,21 @@ void system_header() {
}

} // ignore_system_headers

namespace conditional_op {
RefCountable *provide_ref_ctnbl();
bool bar();

void foo() {
RefCountable *a = bar() ? nullptr : provide_ref_ctnbl();
// expected-warning@-1{{Local variable 'a' is uncounted and unsafe [alpha.webkit.UncountedLocalVarsChecker]}}
RefPtr<RefCountable> b = provide_ref_ctnbl();
{
RefCountable* c = bar() ? nullptr : b.get();
c->method();
RefCountable* d = bar() ? b.get() : nullptr;
d->method();
}
}

} // namespace conditional_op