[clang] 26224ca - [clang][analyzer] Improved PointerSubChecker (#93676)
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cfe-commits at lists.llvm.org
Mon Jun 10 01:21:17 PDT 2024
Author: Balázs Kéri
Date: 2024-06-10T10:21:14+02:00
New Revision: 26224ca2de193dcfd21ede7a846c28ea892b77e3
URL: https://github.com/llvm/llvm-project/commit/26224ca2de193dcfd21ede7a846c28ea892b77e3
DIFF: https://github.com/llvm/llvm-project/commit/26224ca2de193dcfd21ede7a846c28ea892b77e3.diff
LOG: [clang][analyzer] Improved PointerSubChecker (#93676)
The checker is made more exact
(only pointer into array is allowed, check array index)
and more tests are added.
Added:
clang/test/Analysis/pointer-sub.c
Modified:
clang/lib/StaticAnalyzer/Checkers/PointerSubChecker.cpp
clang/test/Analysis/casts.c
clang/test/Analysis/ptr-arith.c
Removed:
################################################################################
diff --git a/clang/lib/StaticAnalyzer/Checkers/PointerSubChecker.cpp b/clang/lib/StaticAnalyzer/Checkers/PointerSubChecker.cpp
index 2438cf30b39b5..b73534136fdf0 100644
--- a/clang/lib/StaticAnalyzer/Checkers/PointerSubChecker.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/PointerSubChecker.cpp
@@ -17,6 +17,7 @@
#include "clang/StaticAnalyzer/Core/Checker.h"
#include "clang/StaticAnalyzer/Core/CheckerManager.h"
#include "clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h"
+#include "clang/StaticAnalyzer/Core/PathSensitive/DynamicExtent.h"
#include "llvm/ADT/StringRef.h"
using namespace clang;
@@ -26,16 +27,88 @@ namespace {
class PointerSubChecker
: public Checker< check::PreStmt<BinaryOperator> > {
const BugType BT{this, "Pointer subtraction"};
+ const llvm::StringLiteral Msg_MemRegionDifferent =
+ "Subtraction of two pointers that do not point into the same array "
+ "is undefined behavior.";
+ const llvm::StringLiteral Msg_LargeArrayIndex =
+ "Using an array index greater than the array size at pointer subtraction "
+ "is undefined behavior.";
+ const llvm::StringLiteral Msg_NegativeArrayIndex =
+ "Using a negative array index at pointer subtraction "
+ "is undefined behavior.";
+ const llvm::StringLiteral Msg_BadVarIndex =
+ "Indexing the address of a variable with other than 1 at this place "
+ "is undefined behavior.";
+
+ bool checkArrayBounds(CheckerContext &C, const Expr *E,
+ const ElementRegion *ElemReg,
+ const MemRegion *Reg) const;
+ void reportBug(CheckerContext &C, const Expr *E,
+ const llvm::StringLiteral &Msg) const;
public:
void checkPreStmt(const BinaryOperator *B, CheckerContext &C) const;
};
}
+bool PointerSubChecker::checkArrayBounds(CheckerContext &C, const Expr *E,
+ const ElementRegion *ElemReg,
+ const MemRegion *Reg) const {
+ if (!ElemReg)
+ return true;
+
+ ProgramStateRef State = C.getState();
+ const MemRegion *SuperReg = ElemReg->getSuperRegion();
+ SValBuilder &SVB = C.getSValBuilder();
+
+ if (SuperReg == Reg) {
+ if (const llvm::APSInt *I = SVB.getKnownValue(State, ElemReg->getIndex());
+ I && (!I->isOne() && !I->isZero()))
+ reportBug(C, E, Msg_BadVarIndex);
+ return false;
+ }
+
+ DefinedOrUnknownSVal ElemCount =
+ getDynamicElementCount(State, SuperReg, SVB, ElemReg->getElementType());
+ auto IndexTooLarge = SVB.evalBinOp(C.getState(), BO_GT, ElemReg->getIndex(),
+ ElemCount, SVB.getConditionType())
+ .getAs<DefinedOrUnknownSVal>();
+ if (IndexTooLarge) {
+ ProgramStateRef S1, S2;
+ std::tie(S1, S2) = C.getState()->assume(*IndexTooLarge);
+ if (S1 && !S2) {
+ reportBug(C, E, Msg_LargeArrayIndex);
+ return false;
+ }
+ }
+ auto IndexTooSmall = SVB.evalBinOp(State, BO_LT, ElemReg->getIndex(),
+ SVB.makeZeroVal(SVB.getArrayIndexType()),
+ SVB.getConditionType())
+ .getAs<DefinedOrUnknownSVal>();
+ if (IndexTooSmall) {
+ ProgramStateRef S1, S2;
+ std::tie(S1, S2) = State->assume(*IndexTooSmall);
+ if (S1 && !S2) {
+ reportBug(C, E, Msg_NegativeArrayIndex);
+ return false;
+ }
+ }
+ return true;
+}
+
+void PointerSubChecker::reportBug(CheckerContext &C, const Expr *E,
+ const llvm::StringLiteral &Msg) const {
+ if (ExplodedNode *N = C.generateNonFatalErrorNode()) {
+ auto R = std::make_unique<PathSensitiveBugReport>(BT, Msg, N);
+ R->addRange(E->getSourceRange());
+ C.emitReport(std::move(R));
+ }
+}
+
void PointerSubChecker::checkPreStmt(const BinaryOperator *B,
CheckerContext &C) const {
// When doing pointer subtraction, if the two pointers do not point to the
- // same memory chunk, emit a warning.
+ // same array, emit a warning.
if (B->getOpcode() != BO_Sub)
return;
@@ -44,28 +117,36 @@ void PointerSubChecker::checkPreStmt(const BinaryOperator *B,
const MemRegion *LR = LV.getAsRegion();
const MemRegion *RR = RV.getAsRegion();
-
- if (!(LR && RR))
+ if (!LR || !RR)
return;
- const MemRegion *BaseLR = LR->getBaseRegion();
- const MemRegion *BaseRR = RR->getBaseRegion();
+ // Allow subtraction of identical pointers.
+ if (LR == RR)
+ return;
- if (BaseLR == BaseRR)
+ // No warning if one operand is unknown.
+ if (isa<SymbolicRegion>(LR) || isa<SymbolicRegion>(RR))
return;
- // Allow arithmetic on
diff erent symbolic regions.
- if (isa<SymbolicRegion>(BaseLR) || isa<SymbolicRegion>(BaseRR))
+ const auto *ElemLR = dyn_cast<ElementRegion>(LR);
+ const auto *ElemRR = dyn_cast<ElementRegion>(RR);
+
+ if (!checkArrayBounds(C, B->getLHS(), ElemLR, RR))
+ return;
+ if (!checkArrayBounds(C, B->getRHS(), ElemRR, LR))
return;
- if (ExplodedNode *N = C.generateNonFatalErrorNode()) {
- constexpr llvm::StringLiteral Msg =
- "Subtraction of two pointers that do not point to the same memory "
- "chunk may cause incorrect result.";
- auto R = std::make_unique<PathSensitiveBugReport>(BT, Msg, N);
- R->addRange(B->getSourceRange());
- C.emitReport(std::move(R));
+ if (ElemLR && ElemRR) {
+ const MemRegion *SuperLR = ElemLR->getSuperRegion();
+ const MemRegion *SuperRR = ElemRR->getSuperRegion();
+ if (SuperLR == SuperRR)
+ return;
+ // Allow arithmetic on
diff erent symbolic regions.
+ if (isa<SymbolicRegion>(SuperLR) || isa<SymbolicRegion>(SuperRR))
+ return;
}
+
+ reportBug(C, B, Msg_MemRegionDifferent);
}
void ento::registerPointerSubChecker(CheckerManager &mgr) {
diff --git a/clang/test/Analysis/casts.c b/clang/test/Analysis/casts.c
index 30cd74be564fd..7dad4edfa89b9 100644
--- a/clang/test/Analysis/casts.c
+++ b/clang/test/Analysis/casts.c
@@ -138,7 +138,9 @@ void multiDimensionalArrayPointerCasts(void) {
clang_analyzer_eval(y1 == y2); // expected-warning{{TRUE}}
// FIXME: should be FALSE (i.e. equal pointers).
+ // FIXME: pointer subtraction warning might be incorrect
clang_analyzer_eval(y1 - y2); // expected-warning{{UNKNOWN}}
+ // expected-warning at -1{{Subtraction of two pointers that do not point into the same array is undefined behavior}}
// FIXME: should be TRUE (i.e. same symbol).
clang_analyzer_eval(*y1 == *y2); // expected-warning{{UNKNOWN}}
@@ -147,7 +149,9 @@ void multiDimensionalArrayPointerCasts(void) {
clang_analyzer_eval(y1 == y3); // expected-warning{{TRUE}}
// FIXME: should be FALSE (i.e. equal pointers).
+ // FIXME: pointer subtraction warning might be incorrect
clang_analyzer_eval(y1 - y3); // expected-warning{{UNKNOWN}}
+ // expected-warning at -1{{Subtraction of two pointers that do not point into the same array is undefined behavior}}
// FIXME: should be TRUE (i.e. same symbol).
clang_analyzer_eval(*y1 == *y3); // expected-warning{{UNKNOWN}}
diff --git a/clang/test/Analysis/pointer-sub.c b/clang/test/Analysis/pointer-sub.c
new file mode 100644
index 0000000000000..9a446547e2868
--- /dev/null
+++ b/clang/test/Analysis/pointer-sub.c
@@ -0,0 +1,120 @@
+// RUN: %clang_analyze_cc1 -analyzer-checker=alpha.core.PointerSub -verify %s
+
+void f1(void) {
+ int x, y, z[10];
+ int d = &y - &x; // expected-warning{{Subtraction of two pointers that do not point into the same array is undefined behavior}}
+ d = z - &y; // expected-warning{{Subtraction of two pointers that do not point into the same array is undefined behavior}}
+ d = &x - &x; // no-warning (subtraction of any two identical pointers is allowed)
+ d = (long *)&x - (long *)&x;
+ d = (&x + 1) - &x; // no-warning ('&x' is like a single-element array)
+ d = &x - (&x + 1); // no-warning
+ d = (&x + 0) - &x; // no-warning
+ d = (&x - 1) - &x; // expected-warning{{Indexing the address of a variable with other than 1 at this place is undefined behavior}}
+ d = (&x + 2) - &x; // expected-warning{{Indexing the address of a variable with other than 1 at this place is undefined behavior}}
+
+ d = (z + 9) - z; // no-warning (pointers to same array)
+ d = (z + 10) - z; // no-warning (pointer to "one after the end")
+ d = (z + 11) - z; // expected-warning{{Using an array index greater than the array size at pointer subtraction is undefined behavior}}
+ d = (z - 1) - z; // expected-warning{{Using a negative array index at pointer subtraction is undefined behavior}}
+}
+
+void f2(void) {
+ int a[10], b[10], c;
+ int *p = &a[2];
+ int *q = &a[8];
+ int d = q - p; // no-warning (pointers into the same array)
+
+ q = &b[3];
+ d = q - p; // expected-warning{{Subtraction of two pointers that}}
+
+ q = a + 10;
+ d = q - p; // no warning (use of pointer to one after the end is allowed)
+ q = a + 11;
+ d = q - a; // expected-warning{{Using an array index greater than the array size at pointer subtraction is undefined behavior}}
+
+ d = &a[4] - a; // no-warning
+ d = &a[2] - p; // no-warning
+ d = &c - p; // expected-warning{{Subtraction of two pointers that}}
+
+ d = (int *)((char *)(&a[4]) + sizeof(int)) - &a[4]; // no-warning (pointers into the same array data)
+ d = (int *)((char *)(&a[4]) + 1) - &a[4]; // expected-warning{{Subtraction of two pointers that}}
+}
+
+void f3(void) {
+ int a[3][4];
+ int d;
+
+ d = &(a[2]) - &(a[1]);
+ d = a[2] - a[1]; // expected-warning{{Subtraction of two pointers that}}
+ d = a[1] - a[1];
+ d = &(a[1][2]) - &(a[1][0]);
+ d = &(a[1][2]) - &(a[0][0]); // expected-warning{{Subtraction of two pointers that}}
+
+ d = (int *)((char *)(&a[2][2]) + sizeof(int)) - &a[2][2]; // expected-warning{{Subtraction of two pointers that}}
+ d = (int *)((char *)(&a[2][2]) + 1) - &a[2][2]; // expected-warning{{Subtraction of two pointers that}}
+ d = (int (*)[4])((char *)&a[2] + sizeof(int (*)[4])) - &a[2]; // expected-warning{{Subtraction of two pointers that}}
+ d = (int (*)[4])((char *)&a[2] + 1) - &a[2]; // expected-warning{{Subtraction of two pointers that}}
+}
+
+void f4(void) {
+ int n = 4, m = 3;
+ int a[n][m];
+ int (*p)[m] = a; // p == &a[0]
+ p += 1; // p == &a[1]
+
+ // FIXME: This is a known problem with -Wpointer-arith (https://github.com/llvm/llvm-project/issues/28328)
+ int d = p - a; // d == 1 // expected-warning{{subtraction of pointers to type 'int[m]' of zero size has undefined behavior}}
+
+ // FIXME: This is a known problem with -Wpointer-arith (https://github.com/llvm/llvm-project/issues/28328)
+ d = &(a[2]) - &(a[1]); // expected-warning{{subtraction of pointers to type 'int[m]' of zero size has undefined behavior}}
+
+ d = a[2] - a[1]; // expected-warning{{Subtraction of two pointers that}}
+}
+
+typedef struct {
+ int a;
+ int b;
+ int c[10];
+ int d[10];
+} S;
+
+void f5(void) {
+ S s;
+ int y;
+ int d;
+
+ d = &s.b - &s.a; // expected-warning{{Subtraction of two pointers that}}
+ d = &s.c[0] - &s.a; // expected-warning{{Subtraction of two pointers that}}
+ d = &s.b - &y; // expected-warning{{Subtraction of two pointers that}}
+ d = &s.c[3] - &s.c[2];
+ d = &s.d[3] - &s.c[2]; // expected-warning{{Subtraction of two pointers that}}
+ d = s.d - s.c; // expected-warning{{Subtraction of two pointers that}}
+
+ S sa[10];
+ d = &sa[2] - &sa[1];
+ d = &sa[2].a - &sa[1].b; // expected-warning{{Subtraction of two pointers that}}
+}
+
+void f6(void) {
+ long long l;
+ char *a1 = (char *)&l;
+ int d = a1[3] - l;
+
+ long long la1[3];
+ long long la2[3];
+ char *pla1 = (char *)la1;
+ char *pla2 = (char *)la2;
+ d = pla1[1] - pla1[0];
+ d = (long long *)&pla1[1] - &l; // expected-warning{{Subtraction of two pointers that}}
+ d = &pla2[3] - &pla1[3]; // expected-warning{{Subtraction of two pointers that}}
+}
+
+void f7(int *p) {
+ int a[10];
+ int d = &a[10] - p; // no-warning ('p' is unknown, even if it cannot point into 'a')
+}
+
+void f8(int n) {
+ int a[10];
+ int d = a[n] - a[0];
+}
diff --git a/clang/test/Analysis/ptr-arith.c b/clang/test/Analysis/ptr-arith.c
index 40c8188704e81..f99dfabb07366 100644
--- a/clang/test/Analysis/ptr-arith.c
+++ b/clang/test/Analysis/ptr-arith.c
@@ -1,5 +1,5 @@
-// RUN: %clang_analyze_cc1 -analyzer-checker=alpha.core.FixedAddr,alpha.core.PointerArithm,alpha.core.PointerSub,debug.ExprInspection -Wno-pointer-to-int-cast -verify -triple x86_64-apple-darwin9 -Wno-tautological-pointer-compare -analyzer-config eagerly-assume=false %s
-// RUN: %clang_analyze_cc1 -analyzer-checker=alpha.core.FixedAddr,alpha.core.PointerArithm,alpha.core.PointerSub,debug.ExprInspection -Wno-pointer-to-int-cast -verify -triple i686-apple-darwin9 -Wno-tautological-pointer-compare -analyzer-config eagerly-assume=false %s
+// RUN: %clang_analyze_cc1 -analyzer-checker=alpha.core.FixedAddr,alpha.core.PointerArithm,debug.ExprInspection -Wno-pointer-to-int-cast -verify -triple x86_64-apple-darwin9 -Wno-tautological-pointer-compare -analyzer-config eagerly-assume=false %s
+// RUN: %clang_analyze_cc1 -analyzer-checker=alpha.core.FixedAddr,alpha.core.PointerArithm,debug.ExprInspection -Wno-pointer-to-int-cast -verify -triple i686-apple-darwin9 -Wno-tautological-pointer-compare -analyzer-config eagerly-assume=false %s
void clang_analyzer_eval(int);
void clang_analyzer_dump(int);
@@ -35,16 +35,6 @@ domain_port (const char *domain_b, const char *domain_e,
return port;
}
-void f3(void) {
- int x, y;
- int d = &y - &x; // expected-warning{{Subtraction of two pointers that do not point to the same memory chunk may cause incorrect result}}
-
- int a[10];
- int *p = &a[2];
- int *q = &a[8];
- d = q-p; // no-warning
-}
-
void f4(void) {
int *p;
p = (int*) 0x10000; // expected-warning{{Using a fixed address is not portable because that address will probably not be valid in all environments or platforms}}
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