[PATCH] Fix to PR5683 - issue diagnostic for pointer subtraction with type of size zero.
Serge Pavlov
sepavloff at gmail.com
Wed Jun 19 20:12:51 PDT 2013
Friendly ping.
2013/4/10 Serge Pavlov <sepavloff at gmail.com>
> Small code enhancement: use overloaded operators of QualType
>
> Hi rsmith,
>
> http://llvm-reviews.chandlerc.com/D637
>
> CHANGE SINCE LAST DIFF
> http://llvm-reviews.chandlerc.com/D637?vs=1563&id=1580#toc
>
> Files:
> include/clang/Basic/DiagnosticSemaKinds.td
> lib/AST/ExprConstant.cpp
> lib/Sema/SemaExpr.cpp
> test/Sema/empty1.c
>
> Index: include/clang/Basic/DiagnosticSemaKinds.td
> ===================================================================
> --- include/clang/Basic/DiagnosticSemaKinds.td
> +++ include/clang/Basic/DiagnosticSemaKinds.td
> @@ -3976,6 +3976,9 @@
> def warn_offsetof_non_standardlayout_type : ExtWarn<
> "offset of on non-standard-layout type %0">, InGroup<InvalidOffsetof>;
> def err_offsetof_bitfield : Error<"cannot compute offset of bit-field
> %0">;
> +def warn_sub_ptr_zero_size_types : Warning<
> + "subtraction of pointers to type %0 with zero size has undefined
> behavior">,
> + InGroup<PointerArith>;
>
> def warn_floatingpoint_eq : Warning<
> "comparing floating point with == or != is unsafe">,
> Index: lib/AST/ExprConstant.cpp
> ===================================================================
> --- lib/AST/ExprConstant.cpp
> +++ lib/AST/ExprConstant.cpp
> @@ -5003,6 +5003,12 @@
> if (!HandleSizeof(Info, E->getExprLoc(), ElementType,
> ElementSize))
> return false;
>
> + // Empty struct or union in C has size 0 (GCC extension). Meaning
> of
> + // pointer difference in such case is unspecified, so set
> ElementSize
> + // to 1 to avoid division by zero.
> + if (ElementSize.isZero())
> + ElementSize = CharUnits::One();
> +
> // FIXME: LLVM and GCC both compute LHSOffset - RHSOffset at
> runtime,
> // and produce incorrect results when it overflows. Such behavior
> // appears to be non-conforming, but is common, so perhaps we
> should
> Index: lib/Sema/SemaExpr.cpp
> ===================================================================
> --- lib/Sema/SemaExpr.cpp
> +++ lib/Sema/SemaExpr.cpp
> @@ -6734,6 +6734,19 @@
> LHS.get(), RHS.get()))
> return QualType();
>
> + if (!getLangOpts().CPlusPlus) {
> + // If pointee type is a structure or union of zero size (GCC
> extension),
> + // the subtraction does not make sense.
> + if (!rpointee->isVoidType() && !rpointee->isFunctionType()) {
> + CharUnits ElementSize = Context.getTypeSizeInChars(rpointee);
> + if (ElementSize.isZero()) {
> + Diag(Loc,diag::warn_sub_ptr_zero_size_types)
> + << rpointee.getUnqualifiedType()
> + << LHS.get()->getSourceRange() <<
> RHS.get()->getSourceRange();
> + }
> + }
> + }
> +
> if (CompLHSTy) *CompLHSTy = LHS.get()->getType();
> return Context.getPointerDiffType();
> }
> Index: test/Sema/empty1.c
> ===================================================================
> --- /dev/null
> +++ test/Sema/empty1.c
> @@ -0,0 +1,53 @@
> +// RUN: %clang_cc1 %s -fsyntax-only -verify
> +
> +struct empty {};
> +struct empty_2 {};
> +union empty_u {};
> +
> +struct empty* func_1p (struct empty* x) {
> + return x - 5;
> +}
> +
> +int func_1 () {
> + struct empty v[1];
> + return v - v; // expected-warning {{subtraction of pointers to type
> 'struct empty' with zero size has undefined behavior}}
> +}
> +
> +int func_2 (struct empty* x) {
> + return 1 + x - x; // expected-warning {{subtraction of pointers to
> type 'struct empty' with zero size has undefined behavior}}
> +}
> +
> +int func_3 (struct empty* x, struct empty* y) {
> + return x - y; // expected-warning {{subtraction of pointers to type
> 'struct empty' with zero size has undefined behavior}}
> +}
> +
> +int func_4 (struct empty* x, const struct empty* y) {
> + return x - y; // expected-warning {{subtraction of pointers to type
> 'struct empty' with zero size has undefined behavior}}
> +}
> +
> +int func_5 (volatile struct empty* x, const struct empty* y) {
> + return x - y; // expected-warning {{subtraction of pointers to type
> 'struct empty' with zero size has undefined behavior}}
> +}
> +
> +int func_6 (struct empty* x, struct empty_2* y) {
> + return x - y; // expected-error {{'struct empty *' and 'struct empty_2
> *' are not pointers to compatible types}}
> +}
> +
> +int func_7 () {
> + union empty_u v[1];
> + return v - v; // expected-warning {{subtraction of pointers to type
> 'union empty_u' with zero size has undefined behavior}}
> +}
> +
> +struct A; // expected-note {{forward declaration of 'struct A'}}
> +
> +int func_8 (struct A* x, struct A* y) {
> + return x - y; // expected-error {{arithmetic on a pointer to an
> incomplete type 'struct A'}}
> +}
> +
> +int func_9 (struct empty (*x)[10], struct empty (*y)[10]) {
> + return x - y; // expected-warning {{subtraction of pointers to type
> 'struct empty [10]' with zero size has undefined behavior}}
> +}
> +
> +int func_10 (struct empty (*x)[], struct empty (*y)[]) {
> + return x - y; // expected-error {{arithmetic on a pointer to an
> incomplete type 'struct empty []'}}
> +}
>
--
Thanks,
--Serge
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