This revision was not accepted when it landed; it landed in state "Needs
Review".
This revision was automatically updated to reflect the committed changes.
Closed by commit rG9cb00b9ecbe7: Reland Produce warning for performing pointer
arithmetic on a null pointer. (authored by jamieschmeiser).
Changed prior to commit:
https://reviews.llvm.org/D98798?vs=346751&id=360116#toc
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D98798/new/
https://reviews.llvm.org/D98798
Files:
clang/docs/ReleaseNotes.rst
clang/include/clang/Basic/DiagnosticGroups.td
clang/include/clang/Basic/DiagnosticSemaKinds.td
clang/lib/Sema/SemaExpr.cpp
clang/test/Sema/Inputs/pointer-subtraction.h
clang/test/Sema/pointer-subtraction.c
clang/test/Sema/pointer-subtraction.cpp
Index: clang/test/Sema/pointer-subtraction.cpp
===================================================================
--- /dev/null
+++ clang/test/Sema/pointer-subtraction.cpp
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 %s -fsyntax-only -verify -pedantic -Wextra -std=c++11 -isystem %S/Inputs
+// RUN: %clang_cc1 %s -fsyntax-only -verify -pedantic -Wnull-pointer-subtraction -std=c++11 -isystem %S/Inputs
+// RUN: %clang_cc1 %s -fsyntax-only -verify -pedantic -Wextra -std=c++11 -isystem %S/Inputs -Wsystem-headers -DSYSTEM_WARNINGS
+// RUN: %clang_cc1 %s -fsyntax-only -verify -pedantic -Wnull-pointer-subtraction -std=c++11 -isystem %S/Inputs -Wsystem-headers -DSYSTEM_WARNINGS
+
+#include <pointer-subtraction.h>
+
+void a() {
+ char *f = (char *)0;
+ f = (char *)((char *)0 - f); // expected-warning {{performing pointer subtraction with a null pointer may have undefined behavior}}
+ f = (char *)(f - (char *)0); // expected-warning {{performing pointer subtraction with a null pointer may have undefined behavior}}
+ f = (char *)((char *)0 - (char *)0); // valid in C++
+
+#ifndef SYSTEM_WARNINGS
+ SYSTEM_MACRO(f);
+#else
+ SYSTEM_MACRO(f); // expected-warning {{performing pointer subtraction with a null pointer may have undefined behavior}}
+#endif
+}
Index: clang/test/Sema/pointer-subtraction.c
===================================================================
--- /dev/null
+++ clang/test/Sema/pointer-subtraction.c
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 %s -fsyntax-only -verify -pedantic -Wextra -std=c11 -isystem %S/Inputs
+// RUN: %clang_cc1 %s -fsyntax-only -verify -pedantic -Wnull-pointer-subtraction -std=c11 -isystem %S/Inputs
+// RUN: %clang_cc1 %s -fsyntax-only -verify -pedantic -Wextra -std=c11 -isystem %S/Inputs -Wsystem-headers -DSYSTEM_WARNINGS
+// RUN: %clang_cc1 %s -fsyntax-only -verify -pedantic -Wnull-pointer-subtraction -std=c11 -isystem %S/Inputs -Wsystem-headers -DSYSTEM_WARNINGS
+
+#include <pointer-subtraction.h>
+
+void a() {
+ char *f = (char *)0;
+ f = (char *)((char *)0 - f); // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
+ f = (char *)(f - (char *)0); // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
+ f = (char *)((char *)0 - (char *)0); // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}} expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
+
+#ifndef SYSTEM_WARNINGS
+ SYSTEM_MACRO(f);
+#else
+ SYSTEM_MACRO(f); // expected-warning {{performing pointer subtraction with a null pointer has undefined behavior}}
+#endif
+}
Index: clang/test/Sema/Inputs/pointer-subtraction.h
===================================================================
--- /dev/null
+++ clang/test/Sema/Inputs/pointer-subtraction.h
@@ -0,0 +1 @@
+#define SYSTEM_MACRO(x) (x) = (char *)((char *)0 - (x))
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -10432,6 +10432,22 @@
<< S.getLangOpts().CPlusPlus << Pointer->getSourceRange();
}
+/// Diagnose invalid subraction on a null pointer.
+///
+static void diagnoseSubtractionOnNullPointer(Sema &S, SourceLocation Loc,
+ Expr *Pointer, bool BothNull) {
+ // Null - null is valid in C++ [expr.add]p7
+ if (BothNull && S.getLangOpts().CPlusPlus)
+ return;
+
+ // Is this s a macro from a system header?
+ if (S.Diags.getSuppressSystemWarnings() && S.SourceMgr.isInSystemMacro(Loc))
+ return;
+
+ S.Diag(Loc, diag::warn_pointer_sub_null_ptr)
+ << S.getLangOpts().CPlusPlus << Pointer->getSourceRange();
+}
+
/// Diagnose invalid arithmetic on two function pointers.
static void diagnoseArithmeticOnTwoFunctionPointers(Sema &S, SourceLocation Loc,
Expr *LHS, Expr *RHS) {
@@ -10863,7 +10879,16 @@
LHS.get(), RHS.get()))
return QualType();
- // FIXME: Add warnings for nullptr - ptr.
+ bool LHSIsNullPtr = LHS.get()->IgnoreParenCasts()->isNullPointerConstant(
+ Context, Expr::NPC_ValueDependentIsNotNull);
+ bool RHSIsNullPtr = RHS.get()->IgnoreParenCasts()->isNullPointerConstant(
+ Context, Expr::NPC_ValueDependentIsNotNull);
+
+ // Subtracting nullptr or from nullptr is suspect
+ if (LHSIsNullPtr)
+ diagnoseSubtractionOnNullPointer(*this, Loc, LHS.get(), RHSIsNullPtr);
+ if (RHSIsNullPtr)
+ diagnoseSubtractionOnNullPointer(*this, Loc, RHS.get(), LHSIsNullPtr);
// The pointee type may have zero size. As an extension, a structure or
// union may have zero size or an array may have zero length. In this
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6390,6 +6390,9 @@
def warn_gnu_null_ptr_arith : Warning<
"arithmetic on a null pointer treated as a cast from integer to pointer is a GNU extension">,
InGroup<NullPointerArithmetic>, DefaultIgnore;
+def warn_pointer_sub_null_ptr : Warning<
+ "performing pointer subtraction with a null pointer %select{has|may have}0 undefined behavior">,
+ InGroup<NullPointerSubtraction>, DefaultIgnore;
def err_kernel_invalidates_sycl_unique_stable_name
: Error<"kernel instantiation changes the result of an evaluated "
"'__builtin_sycl_unique_stable_name'">;
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -487,6 +487,7 @@
def : DiagGroup<"nonportable-cfstrings">;
def NonVirtualDtor : DiagGroup<"non-virtual-dtor">;
def NullPointerArithmetic : DiagGroup<"null-pointer-arithmetic">;
+def NullPointerSubtraction : DiagGroup<"null-pointer-subtraction">;
def : DiagGroup<"effc++", [NonVirtualDtor]>;
def OveralignedType : DiagGroup<"over-aligned">;
def OldStyleCast : DiagGroup<"old-style-cast">;
@@ -932,6 +933,7 @@
UnusedParameter,
UnusedButSetParameter,
NullPointerArithmetic,
+ NullPointerSubtraction,
EmptyInitStatement,
StringConcatation,
FUseLdPath,
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -76,6 +76,9 @@
file contains frame size information for each function defined in the source
file.
+- ``-Wnull-pointer-subtraction`` emits warning when user code may have
+ undefined behaviour due to subtraction involving a null pointer.
+
Deprecated Compiler Flags
-------------------------
@@ -92,6 +95,7 @@
instead. ``-B``'s other GCC-compatible semantics are preserved:
``$prefix/$triple-$file`` and ``$prefix$file`` are searched for executables,
libraries, includes, and data files used by the compiler.
+- ``-Wextra`` now also implies ``-Wnull-pointer-subtraction.``
Removed Compiler Flags
-------------------------
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