In this case Clang is complaining about
memset(complicated-expr, 0, 0);
which means that transposing the last two arguments would not "fix"
anything. Clang ought to not complain in this case.
It doesn't have anything to do with coming from a macro; it's just that
*both* arguments are zero.
(I would also expect that `memset(complicated-expr, (unsigned char)fill,
(size_t)0)` shouldn't warn, either. But we had some disagreement that casts
to `(unsigned char)` resp. `(size_t)` should be the right way to shut up
the warning in the first place...)
Basically Clang should only be suggesting a swap (and thus complaining at
all) in the case that swapping the arguments would actually improve the
situation.
–Arthur
On Sat, Jul 21, 2018 at 1:33 PM, Nico Weber via cfe-commits <
cfe-commits@lists.llvm.org> wrote:
> This has a false positive on ffmpeg:
>
> ../../third_party/ffmpeg/libavcodec/options.c:273:64: error: 'size'
> argument to memset is '0'; did you mean to transpose the last two
> arguments? [-Werror,-Wmemset-transposed-args]
> alloc_and_copy_or_fail(intra_matrix, 64 * sizeof(int16_t), 0);
>
> With:
>
> #define alloc_and_copy_or_fail(obj, size, pad) \
> if (src->obj && size > 0) { \
> dest->obj = av_malloc(size + pad); \
> if (!dest->obj) \
> goto fail; \
> memcpy(dest->obj, src->obj, size); \
> if (pad) \
> memset(((uint8_t *) dest->obj) + size, 0, pad); \
> }
>
> (https://cs.chromium.org/chromium/src/third_party/
> ffmpeg/libavcodec/options.c?q=alloc_and_copy_or_fail&sq=
> package:chromium&g=0&l=261 ; https://bugs.chromium.org/p/
> chromium/issues/detail?id=866202)
>
> Maybe the warning shouldn't fire if the memset is from a macro?
>
> On Thu, Jul 19, 2018 at 12:51 PM Erik Pilkington via cfe-commits <
> cfe-commits@lists.llvm.org> wrote:
>
>> Author: epilk
>> Date: Thu Jul 19 09:46:15 2018
>> New Revision: 337470
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=337470&view=rev
>> Log:
>> [Sema] Add a new warning, -Wmemset-transposed-args
>>
>> This diagnoses calls to memset that have the second and third arguments
>> transposed, for example:
>>
>> memset(buf, sizeof(buf), 0);
>>
>> This is done by checking if the third argument is a literal 0, or if the
>> second
>> is a sizeof expression (and the third isn't). The first check is also
>> done for
>> calls to bzero.
>>
>> Differential revision: https://reviews.llvm.org/D49112
>>
>> Added:
>> cfe/trunk/test/Sema/transpose-memset.c
>> Modified:
>> cfe/trunk/include/clang/Basic/DiagnosticGroups.td
>> cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>> cfe/trunk/lib/Sema/SemaChecking.cpp
>>
>> Modified: cfe/trunk/include/clang/Basic/DiagnosticGroups.td
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/
>> clang/Basic/DiagnosticGroups.td?rev=337470&r1=337469&r2=337470&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/include/clang/Basic/DiagnosticGroups.td (original)
>> +++ cfe/trunk/include/clang/Basic/DiagnosticGroups.td Thu Jul 19
>> 09:46:15 2018
>> @@ -443,6 +443,13 @@ def : DiagGroup<"synth">;
>> def SizeofArrayArgument : DiagGroup<"sizeof-array-argument">;
>> def SizeofArrayDecay : DiagGroup<"sizeof-array-decay">;
>> def SizeofPointerMemaccess : DiagGroup<"sizeof-pointer-memaccess">;
>> +def MemsetTransposedArgs : DiagGroup<"memset-transposed-args">;
>> +def DynamicClassMemaccess : DiagGroup<"dynamic-class-memaccess">;
>> +def NonTrivialMemaccess : DiagGroup<"nontrivial-memaccess">;
>> +def SuspiciousBzero : DiagGroup<"suspicious-bzero">;
>> +def SuspiciousMemaccess : DiagGroup<"suspicious-memaccess",
>> + [SizeofPointerMemaccess, DynamicClassMemaccess,
>> + NonTrivialMemaccess, MemsetTransposedArgs, SuspiciousBzero]>;
>> def StaticInInline : DiagGroup<"static-in-inline">;
>> def StaticLocalInInline : DiagGroup<"static-local-in-inline">;
>> def GNUStaticFloatInit : DiagGroup<"gnu-static-float-init">;
>>
>> Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/
>> DiagnosticSemaKinds.td?rev=337470&r1=337469&r2=337470&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
>> +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Thu Jul 19
>> 09:46:15 2018
>> @@ -619,14 +619,14 @@ def warn_cstruct_memaccess : Warning<
>> "%select{destination for|source of|first operand of|second operand
>> of}0 this "
>> "%1 call is a pointer to record %2 that is not trivial to "
>> "%select{primitive-default-initialize|primitive-copy}3">,
>> - InGroup<DiagGroup<"nontrivial-memaccess">>;
>> + InGroup<NonTrivialMemaccess>;
>> def note_nontrivial_field : Note<
>> "field is non-trivial to %select{copy|default-initialize}0">;
>> def warn_dyn_class_memaccess : Warning<
>> "%select{destination for|source of|first operand of|second operand
>> of}0 this "
>> "%1 call is a pointer to %select{|class containing a }2dynamic class
>> %3; "
>> "vtable pointer will be %select{overwritten|copied|moved|compared}4">,
>> - InGroup<DiagGroup<"dynamic-class-memaccess">>;
>> + InGroup<DynamicClassMemaccess>;
>> def note_bad_memaccess_silence : Note<
>> "explicitly cast the pointer to silence this warning">;
>> def warn_sizeof_pointer_expr_memaccess : Warning<
>> @@ -655,7 +655,19 @@ def note_memsize_comparison_paren : Note
>> "did you mean to compare the result of %0 instead?">;
>> def note_memsize_comparison_cast_silence : Note<
>> "explicitly cast the argument to size_t to silence this warning">;
>> -
>> +def warn_suspicious_sizeof_memset : Warning<
>> + "%select{'size' argument to memset is '0'|"
>> + "setting buffer to a 'sizeof' expression}0"
>> + "; did you mean to transpose the last two arguments?">,
>> + InGroup<MemsetTransposedArgs>;
>> +def note_suspicious_sizeof_memset_silence : Note<
>> + "%select{parenthesize the third argument|"
>> + "cast the second argument to 'int'}0 to silence">;
>> +def warn_suspicious_bzero_size : Warning<"'size' argument to bzero is
>> '0'">,
>> + InGroup<SuspiciousBzero>;
>> +def note_suspicious_bzero_size_silence : Note<
>> + "parenthesize the second argument to silence">;
>> +
>> def warn_strncat_large_size : Warning<
>> "the value of the size argument in 'strncat' is too large, might lead
>> to a "
>> "buffer overflow">, InGroup<StrncatSize>;
>>
>> Modified: cfe/trunk/lib/Sema/SemaChecking.cpp
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/
>> SemaChecking.cpp?rev=337470&r1=337469&r2=337470&view=diff
>> ============================================================
>> ==================
>> --- cfe/trunk/lib/Sema/SemaChecking.cpp (original)
>> +++ cfe/trunk/lib/Sema/SemaChecking.cpp Thu Jul 19 09:46:15 2018
>> @@ -8629,24 +8629,26 @@ static const CXXRecordDecl *getContained
>> return nullptr;
>> }
>>
>> +static const UnaryExprOrTypeTraitExpr *getAsSizeOfExpr(const Expr *E) {
>> + if (const auto *Unary = dyn_cast<UnaryExprOrTypeTraitExpr>(E))
>> + if (Unary->getKind() == UETT_SizeOf)
>> + return Unary;
>> + return nullptr;
>> +}
>> +
>> /// If E is a sizeof expression, returns its argument expression,
>> /// otherwise returns NULL.
>> static const Expr *getSizeOfExprArg(const Expr *E) {
>> - if (const UnaryExprOrTypeTraitExpr *SizeOf =
>> - dyn_cast<UnaryExprOrTypeTraitExpr>(E))
>> - if (SizeOf->getKind() == UETT_SizeOf && !SizeOf->isArgumentType())
>> + if (const UnaryExprOrTypeTraitExpr *SizeOf = getAsSizeOfExpr(E))
>> + if (!SizeOf->isArgumentType())
>> return SizeOf->getArgumentExpr()->IgnoreParenImpCasts();
>> -
>> return nullptr;
>> }
>>
>> /// If E is a sizeof expression, returns its argument type.
>> static QualType getSizeOfArgType(const Expr *E) {
>> - if (const UnaryExprOrTypeTraitExpr *SizeOf =
>> - dyn_cast<UnaryExprOrTypeTraitExpr>(E))
>> - if (SizeOf->getKind() == UETT_SizeOf)
>> - return SizeOf->getTypeOfArgument();
>> -
>> + if (const UnaryExprOrTypeTraitExpr *SizeOf = getAsSizeOfExpr(E))
>> + return SizeOf->getTypeOfArgument();
>> return QualType();
>> }
>>
>> @@ -8742,6 +8744,86 @@ struct SearchNonTrivialToCopyField
>>
>> }
>>
>> +/// Detect if \c SizeofExpr is likely to calculate the sizeof an object.
>> +static bool doesExprLikelyComputeSize(const Expr *SizeofExpr) {
>> + SizeofExpr = SizeofExpr->IgnoreParenImpCasts();
>> +
>> + if (const auto *BO = dyn_cast<BinaryOperator>(SizeofExpr)) {
>> + if (BO->getOpcode() != BO_Mul && BO->getOpcode() != BO_Add)
>> + return false;
>> +
>> + return doesExprLikelyComputeSize(BO->getLHS()) ||
>> + doesExprLikelyComputeSize(BO->getRHS());
>> + }
>> +
>> + return getAsSizeOfExpr(SizeofExpr) != nullptr;
>> +}
>> +
>> +/// Check if the ArgLoc originated from a macro passed to the call at
>> CallLoc.
>> +///
>> +/// \code
>> +/// #define MACRO 0
>> +/// foo(MACRO);
>> +/// foo(0);
>> +/// \endcode
>> +///
>> +/// This should return true for the first call to foo, but not for the
>> second
>> +/// (regardless of whether foo is a macro or function).
>> +static bool isArgumentExpandedFromMacro(SourceManager &SM,
>> + SourceLocation CallLoc,
>> + SourceLocation ArgLoc) {
>> + if (!CallLoc.isMacroID())
>> + return SM.getFileID(CallLoc) != SM.getFileID(ArgLoc);
>> +
>> + return SM.getFileID(SM.getImmediateMacroCallerLoc(CallLoc)) !=
>> + SM.getFileID(SM.getImmediateMacroCallerLoc(ArgLoc));
>> +}
>> +
>> +/// Diagnose cases like 'memset(buf, sizeof(buf), 0)', which should have
>> the
>> +/// last two arguments transposed.
>> +static void CheckMemaccessSize(Sema &S, unsigned BId, const CallExpr
>> *Call) {
>> + if (BId != Builtin::BImemset && BId != Builtin::BIbzero)
>> + return;
>> +
>> + const Expr *SizeArg =
>> + Call->getArg(BId == Builtin::BImemset ? 2 : 1)->IgnoreImpCasts();
>> +
>> + // If we're memsetting or bzeroing 0 bytes, then this is likely an
>> error.
>> + SourceLocation CallLoc = Call->getRParenLoc();
>> + SourceManager &SM = S.getSourceManager();
>> + if (isa<IntegerLiteral>(SizeArg) &&
>> + cast<IntegerLiteral>(SizeArg)->getValue() == 0 &&
>> + !isArgumentExpandedFromMacro(SM, CallLoc, SizeArg->getExprLoc()))
>> {
>> +
>> + SourceLocation DiagLoc = SizeArg->getExprLoc();
>> +
>> + // Some platforms #define bzero to __builtin_memset. See if this is
>> the
>> + // case, and if so, emit a better diagnostic.
>> + if (BId == Builtin::BIbzero ||
>> + (CallLoc.isMacroID() && Lexer::getImmediateMacroName(
>> + CallLoc, SM, S.getLangOpts()) ==
>> "bzero")) {
>> + S.Diag(DiagLoc, diag::warn_suspicious_bzero_size);
>> + S.Diag(DiagLoc, diag::note_suspicious_bzero_size_silence);
>> + } else {
>> + S.Diag(DiagLoc, diag::warn_suspicious_sizeof_memset) << 0;
>> + S.Diag(DiagLoc, diag::note_suspicious_sizeof_memset_silence) << 0;
>> + }
>> + return;
>> + }
>> +
>> + // If the second argument to a memset is a sizeof expression and the
>> third
>> + // isn't, this is also likely an error. This should catch
>> + // 'memset(buf, sizeof(buf), 0xff)'.
>> + if (BId == Builtin::BImemset &&
>> + doesExprLikelyComputeSize(Call->getArg(1)) &&
>> + !doesExprLikelyComputeSize(Call->getArg(2))) {
>> + SourceLocation DiagLoc = Call->getArg(1)->getExprLoc();
>> + S.Diag(DiagLoc, diag::warn_suspicious_sizeof_memset) << 1;
>> + S.Diag(DiagLoc, diag::note_suspicious_sizeof_memset_silence) << 1;
>> + return;
>> + }
>> +}
>> +
>> /// Check for dangerous or invalid arguments to memset().
>> ///
>> /// This issues warnings on known problematic, dangerous or unspecified
>> @@ -8771,6 +8853,9 @@ void Sema::CheckMemaccessArguments(const
>> Call->getLocStart(),
>> Call->getRParenLoc()))
>> return;
>>
>> + // Catch cases like 'memset(buf, sizeof(buf), 0)'.
>> + CheckMemaccessSize(*this, BId, Call);
>> +
>> // We have special checking when the length is a sizeof expression.
>> QualType SizeOfArgTy = getSizeOfArgType(LenExpr);
>> const Expr *SizeOfArg = getSizeOfExprArg(LenExpr);
>>
>> Added: cfe/trunk/test/Sema/transpose-memset.c
>> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/
>> transpose-memset.c?rev=337470&view=auto
>> ============================================================
>> ==================
>> --- cfe/trunk/test/Sema/transpose-memset.c (added)
>> +++ cfe/trunk/test/Sema/transpose-memset.c Thu Jul 19 09:46:15 2018
>> @@ -0,0 +1,60 @@
>> +// RUN: %clang_cc1 -Wmemset-transposed-args -verify %s
>> +// RUN: %clang_cc1 -xc++ -Wmemset-transposed-args -verify %s
>> +
>> +#define memset(...) __builtin_memset(__VA_ARGS__)
>> +#define bzero(x,y) __builtin_memset(x, 0, y)
>> +#define real_bzero(x,y) __builtin_bzero(x,y)
>> +
>> +int array[10];
>> +int *ptr;
>> +
>> +int main() {
>> + memset(array, sizeof(array), 0); // expected-warning{{'size' argument
>> to memset is '0'; did you mean to transpose the last two arguments?}}
>> expected-note{{parenthesize the third argument to silence}}
>> + memset(array, sizeof(array), 0xff); // expected-warning{{setting
>> buffer to a 'sizeof' expression; did you mean to transpose the last two
>> arguments?}} expected-note{{cast the second argument to 'int' to silence}}
>> + memset(ptr, sizeof(ptr), 0); // expected-warning{{'size' argument to
>> memset is '0'; did you mean to transpose the last two arguments?}}
>> expected-note{{parenthesize the third argument to silence}}
>> + memset(ptr, sizeof(*ptr) * 10, 1); // expected-warning{{setting buffer
>> to a 'sizeof' expression; did you mean to transpose the last two
>> arguments?}} expected-note{{cast the second argument to 'int' to silence}}
>> + memset(ptr, 10 * sizeof(int *), 1); // expected-warning{{setting
>> buffer to a 'sizeof' expression; did you mean to transpose the last two
>> arguments?}} expected-note{{cast the second argument to 'int' to silence}}
>> + memset(ptr, 10 * sizeof(int *) + 10, 0xff); //
>> expected-warning{{setting buffer to a 'sizeof' expression; did you mean to
>> transpose the last two arguments?}} expected-note{{cast the second argument
>> to 'int' to silence}}
>> + memset(ptr, sizeof(char) * sizeof(int *), 0xff); //
>> expected-warning{{setting buffer to a 'sizeof' expression; did you mean to
>> transpose the last two arguments?}} expected-note{{cast the second argument
>> to 'int' to silence}}
>> + memset(array, sizeof(array), sizeof(array)); // Uh... fine I guess.
>> + memset(array, 0, sizeof(array));
>> + memset(ptr, 0, sizeof(int *) * 10);
>> + memset(array, (int)sizeof(array), (0)); // no warning
>> + memset(array, (int)sizeof(array), 32); // no warning
>> + memset(array, 32, (0)); // no warning
>> +
>> + bzero(ptr, 0); // expected-warning{{'size' argument to bzero is '0'}}
>> expected-note{{parenthesize the second argument to silence}}
>> + real_bzero(ptr, 0); // expected-warning{{'size' argument to bzero is
>> '0'}} expected-note{{parenthesize the second argument to silence}}
>> +}
>> +
>> +void macros() {
>> +#define ZERO 0
>> + int array[10];
>> + memset(array, 0xff, ZERO); // no warning
>> + // Still emit a diagnostic for memsetting a sizeof expression:
>> + memset(array, sizeof(array), ZERO); // expected-warning{{'sizeof'}}
>> expected-note{{cast}}
>> + bzero(array, ZERO); // no warning
>> + real_bzero(array, ZERO); // no warning
>> +#define NESTED_DONT_DIAG \
>> + memset(array, 0xff, ZERO); \
>> + real_bzero(array, ZERO);
>> +
>> + NESTED_DONT_DIAG;
>> +
>> +#define NESTED_DO_DIAG \
>> + memset(array, 0xff, 0); \
>> + real_bzero(array, 0)
>> +
>> + NESTED_DO_DIAG; // expected-warning{{'size' argument to memset}}
>> expected-warning{{'size' argument to bzero}} expected-note2{{parenthesize}}
>> +
>> +#define FN_MACRO(p) \
>> + memset(array, 0xff, p)
>> +
>> + FN_MACRO(ZERO);
>> + FN_MACRO(0); // FIXME: should we diagnose this?
>> +
>> + __builtin_memset(array, 0, ZERO); // no warning
>> + __builtin_bzero(array, ZERO);
>> + __builtin_memset(array, 0, 0); // expected-warning{{'size' argument to
>> memset}} // expected-note{{parenthesize}}
>> + __builtin_bzero(array, 0); // expected-warning{{'size' argument to
>> bzero}} // expected-note{{parenthesize}}
>> +}
>>
>>
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>
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