SemaChecking.cpp revision 5ac4dff56e4d241ec47d086fcc646aca4caf9ffd
1//===--- SemaChecking.cpp - Extra Semantic Checking -----------------------===// 2// 3// The LLVM Compiler Infrastructure 4// 5// This file is distributed under the University of Illinois Open Source 6// License. See LICENSE.TXT for details. 7// 8//===----------------------------------------------------------------------===// 9// 10// This file implements extra semantic analysis beyond what is enforced 11// by the C type system. 12// 13//===----------------------------------------------------------------------===// 14 15#include "Sema.h" 16#include "clang/AST/ASTContext.h" 17#include "clang/AST/DeclObjC.h" 18#include "clang/AST/ExprCXX.h" 19#include "clang/AST/ExprObjC.h" 20#include "clang/Lex/LiteralSupport.h" 21#include "clang/Lex/Preprocessor.h" 22using namespace clang; 23 24/// getLocationOfStringLiteralByte - Return a source location that points to the 25/// specified byte of the specified string literal. 26/// 27/// Strings are amazingly complex. They can be formed from multiple tokens and 28/// can have escape sequences in them in addition to the usual trigraph and 29/// escaped newline business. This routine handles this complexity. 30/// 31SourceLocation Sema::getLocationOfStringLiteralByte(const StringLiteral *SL, 32 unsigned ByteNo) const { 33 assert(!SL->isWide() && "This doesn't work for wide strings yet"); 34 35 // Loop over all of the tokens in this string until we find the one that 36 // contains the byte we're looking for. 37 unsigned TokNo = 0; 38 while (1) { 39 assert(TokNo < SL->getNumConcatenated() && "Invalid byte number!"); 40 SourceLocation StrTokLoc = SL->getStrTokenLoc(TokNo); 41 42 // Get the spelling of the string so that we can get the data that makes up 43 // the string literal, not the identifier for the macro it is potentially 44 // expanded through. 45 SourceLocation StrTokSpellingLoc = SourceMgr.getSpellingLoc(StrTokLoc); 46 47 // Re-lex the token to get its length and original spelling. 48 std::pair<FileID, unsigned> LocInfo = 49 SourceMgr.getDecomposedLoc(StrTokSpellingLoc); 50 std::pair<const char *,const char *> Buffer = 51 SourceMgr.getBufferData(LocInfo.first); 52 const char *StrData = Buffer.first+LocInfo.second; 53 54 // Create a langops struct and enable trigraphs. This is sufficient for 55 // relexing tokens. 56 LangOptions LangOpts; 57 LangOpts.Trigraphs = true; 58 59 // Create a lexer starting at the beginning of this token. 60 Lexer TheLexer(StrTokSpellingLoc, LangOpts, Buffer.first, StrData, 61 Buffer.second); 62 Token TheTok; 63 TheLexer.LexFromRawLexer(TheTok); 64 65 // Use the StringLiteralParser to compute the length of the string in bytes. 66 StringLiteralParser SLP(&TheTok, 1, PP); 67 unsigned TokNumBytes = SLP.GetStringLength(); 68 69 // If the byte is in this token, return the location of the byte. 70 if (ByteNo < TokNumBytes || 71 (ByteNo == TokNumBytes && TokNo == SL->getNumConcatenated())) { 72 unsigned Offset = 73 StringLiteralParser::getOffsetOfStringByte(TheTok, ByteNo, PP); 74 75 // Now that we know the offset of the token in the spelling, use the 76 // preprocessor to get the offset in the original source. 77 return PP.AdvanceToTokenCharacter(StrTokLoc, Offset); 78 } 79 80 // Move to the next string token. 81 ++TokNo; 82 ByteNo -= TokNumBytes; 83 } 84} 85 86 87/// CheckFunctionCall - Check a direct function call for various correctness 88/// and safety properties not strictly enforced by the C type system. 89Action::OwningExprResult 90Sema::CheckFunctionCall(FunctionDecl *FDecl, CallExpr *TheCall) { 91 OwningExprResult TheCallResult(Owned(TheCall)); 92 // Get the IdentifierInfo* for the called function. 93 IdentifierInfo *FnInfo = FDecl->getIdentifier(); 94 95 // None of the checks below are needed for functions that don't have 96 // simple names (e.g., C++ conversion functions). 97 if (!FnInfo) 98 return move(TheCallResult); 99 100 switch (FDecl->getBuiltinID(Context)) { 101 case Builtin::BI__builtin___CFStringMakeConstantString: 102 assert(TheCall->getNumArgs() == 1 && 103 "Wrong # arguments to builtin CFStringMakeConstantString"); 104 if (CheckObjCString(TheCall->getArg(0))) 105 return ExprError(); 106 return move(TheCallResult); 107 case Builtin::BI__builtin_stdarg_start: 108 case Builtin::BI__builtin_va_start: 109 if (SemaBuiltinVAStart(TheCall)) 110 return ExprError(); 111 return move(TheCallResult); 112 case Builtin::BI__builtin_isgreater: 113 case Builtin::BI__builtin_isgreaterequal: 114 case Builtin::BI__builtin_isless: 115 case Builtin::BI__builtin_islessequal: 116 case Builtin::BI__builtin_islessgreater: 117 case Builtin::BI__builtin_isunordered: 118 if (SemaBuiltinUnorderedCompare(TheCall)) 119 return ExprError(); 120 return move(TheCallResult); 121 case Builtin::BI__builtin_return_address: 122 case Builtin::BI__builtin_frame_address: 123 if (SemaBuiltinStackAddress(TheCall)) 124 return ExprError(); 125 return move(TheCallResult); 126 case Builtin::BI__builtin_shufflevector: 127 return SemaBuiltinShuffleVector(TheCall); 128 // TheCall will be freed by the smart pointer here, but that's fine, since 129 // SemaBuiltinShuffleVector guts it, but then doesn't release it. 130 case Builtin::BI__builtin_prefetch: 131 if (SemaBuiltinPrefetch(TheCall)) 132 return ExprError(); 133 return move(TheCallResult); 134 case Builtin::BI__builtin_object_size: 135 if (SemaBuiltinObjectSize(TheCall)) 136 return ExprError(); 137 } 138 139 // FIXME: This mechanism should be abstracted to be less fragile and 140 // more efficient. For example, just map function ids to custom 141 // handlers. 142 143 // Printf checking. 144 if (const FormatAttr *Format = FDecl->getAttr<FormatAttr>()) { 145 if (Format->getType() == "printf") { 146 bool HasVAListArg = false; 147 if (const FunctionTypeProto *Proto 148 = FDecl->getType()->getAsFunctionTypeProto()) 149 HasVAListArg = !Proto->isVariadic(); 150 CheckPrintfArguments(TheCall, HasVAListArg, Format->getFormatIdx() - 1, 151 Format->getFirstArg() - 1); 152 } 153 } 154 155 return move(TheCallResult); 156} 157 158/// CheckObjCString - Checks that the argument to the builtin 159/// CFString constructor is correct 160bool Sema::CheckObjCString(Expr *Arg) { 161 Arg = Arg->IgnoreParenCasts(); 162 StringLiteral *Literal = dyn_cast<StringLiteral>(Arg); 163 164 if (!Literal || Literal->isWide()) { 165 Diag(Arg->getLocStart(), diag::err_cfstring_literal_not_string_constant) 166 << Arg->getSourceRange(); 167 return true; 168 } 169 170 const char *Data = Literal->getStrData(); 171 unsigned Length = Literal->getByteLength(); 172 173 for (unsigned i = 0; i < Length; ++i) { 174 if (!isascii(Data[i])) { 175 Diag(getLocationOfStringLiteralByte(Literal, i), 176 diag::warn_cfstring_literal_contains_non_ascii_character) 177 << Arg->getSourceRange(); 178 break; 179 } 180 181 if (!Data[i]) { 182 Diag(getLocationOfStringLiteralByte(Literal, i), 183 diag::warn_cfstring_literal_contains_nul_character) 184 << Arg->getSourceRange(); 185 break; 186 } 187 } 188 189 return false; 190} 191 192/// SemaBuiltinVAStart - Check the arguments to __builtin_va_start for validity. 193/// Emit an error and return true on failure, return false on success. 194bool Sema::SemaBuiltinVAStart(CallExpr *TheCall) { 195 Expr *Fn = TheCall->getCallee(); 196 if (TheCall->getNumArgs() > 2) { 197 Diag(TheCall->getArg(2)->getLocStart(), 198 diag::err_typecheck_call_too_many_args) 199 << 0 /*function call*/ << Fn->getSourceRange() 200 << SourceRange(TheCall->getArg(2)->getLocStart(), 201 (*(TheCall->arg_end()-1))->getLocEnd()); 202 return true; 203 } 204 205 if (TheCall->getNumArgs() < 2) { 206 return Diag(TheCall->getLocEnd(), diag::err_typecheck_call_too_few_args) 207 << 0 /*function call*/; 208 } 209 210 // Determine whether the current function is variadic or not. 211 bool isVariadic; 212 if (getCurFunctionDecl()) { 213 if (FunctionTypeProto* FTP = 214 dyn_cast<FunctionTypeProto>(getCurFunctionDecl()->getType())) 215 isVariadic = FTP->isVariadic(); 216 else 217 isVariadic = false; 218 } else { 219 isVariadic = getCurMethodDecl()->isVariadic(); 220 } 221 222 if (!isVariadic) { 223 Diag(Fn->getLocStart(), diag::err_va_start_used_in_non_variadic_function); 224 return true; 225 } 226 227 // Verify that the second argument to the builtin is the last argument of the 228 // current function or method. 229 bool SecondArgIsLastNamedArgument = false; 230 const Expr *Arg = TheCall->getArg(1)->IgnoreParenCasts(); 231 232 if (const DeclRefExpr *DR = dyn_cast<DeclRefExpr>(Arg)) { 233 if (const ParmVarDecl *PV = dyn_cast<ParmVarDecl>(DR->getDecl())) { 234 // FIXME: This isn't correct for methods (results in bogus warning). 235 // Get the last formal in the current function. 236 const ParmVarDecl *LastArg; 237 if (FunctionDecl *FD = getCurFunctionDecl()) 238 LastArg = *(FD->param_end()-1); 239 else 240 LastArg = *(getCurMethodDecl()->param_end()-1); 241 SecondArgIsLastNamedArgument = PV == LastArg; 242 } 243 } 244 245 if (!SecondArgIsLastNamedArgument) 246 Diag(TheCall->getArg(1)->getLocStart(), 247 diag::warn_second_parameter_of_va_start_not_last_named_argument); 248 return false; 249} 250 251/// SemaBuiltinUnorderedCompare - Handle functions like __builtin_isgreater and 252/// friends. This is declared to take (...), so we have to check everything. 253bool Sema::SemaBuiltinUnorderedCompare(CallExpr *TheCall) { 254 if (TheCall->getNumArgs() < 2) 255 return Diag(TheCall->getLocEnd(), diag::err_typecheck_call_too_few_args) 256 << 0 /*function call*/; 257 if (TheCall->getNumArgs() > 2) 258 return Diag(TheCall->getArg(2)->getLocStart(), 259 diag::err_typecheck_call_too_many_args) 260 << 0 /*function call*/ 261 << SourceRange(TheCall->getArg(2)->getLocStart(), 262 (*(TheCall->arg_end()-1))->getLocEnd()); 263 264 Expr *OrigArg0 = TheCall->getArg(0); 265 Expr *OrigArg1 = TheCall->getArg(1); 266 267 // Do standard promotions between the two arguments, returning their common 268 // type. 269 QualType Res = UsualArithmeticConversions(OrigArg0, OrigArg1, false); 270 271 // Make sure any conversions are pushed back into the call; this is 272 // type safe since unordered compare builtins are declared as "_Bool 273 // foo(...)". 274 TheCall->setArg(0, OrigArg0); 275 TheCall->setArg(1, OrigArg1); 276 277 // If the common type isn't a real floating type, then the arguments were 278 // invalid for this operation. 279 if (!Res->isRealFloatingType()) 280 return Diag(OrigArg0->getLocStart(), 281 diag::err_typecheck_call_invalid_ordered_compare) 282 << OrigArg0->getType() << OrigArg1->getType() 283 << SourceRange(OrigArg0->getLocStart(), OrigArg1->getLocEnd()); 284 285 return false; 286} 287 288bool Sema::SemaBuiltinStackAddress(CallExpr *TheCall) { 289 // The signature for these builtins is exact; the only thing we need 290 // to check is that the argument is a constant. 291 SourceLocation Loc; 292 if (!TheCall->getArg(0)->isIntegerConstantExpr(Context, &Loc)) 293 return Diag(Loc, diag::err_stack_const_level) << TheCall->getSourceRange(); 294 295 return false; 296} 297 298/// SemaBuiltinShuffleVector - Handle __builtin_shufflevector. 299// This is declared to take (...), so we have to check everything. 300Action::OwningExprResult Sema::SemaBuiltinShuffleVector(CallExpr *TheCall) { 301 if (TheCall->getNumArgs() < 3) 302 return ExprError(Diag(TheCall->getLocEnd(), 303 diag::err_typecheck_call_too_few_args) 304 << 0 /*function call*/ << TheCall->getSourceRange()); 305 306 QualType FAType = TheCall->getArg(0)->getType(); 307 QualType SAType = TheCall->getArg(1)->getType(); 308 309 if (!FAType->isVectorType() || !SAType->isVectorType()) { 310 Diag(TheCall->getLocStart(), diag::err_shufflevector_non_vector) 311 << SourceRange(TheCall->getArg(0)->getLocStart(), 312 TheCall->getArg(1)->getLocEnd()); 313 return ExprError(); 314 } 315 316 if (Context.getCanonicalType(FAType).getUnqualifiedType() != 317 Context.getCanonicalType(SAType).getUnqualifiedType()) { 318 Diag(TheCall->getLocStart(), diag::err_shufflevector_incompatible_vector) 319 << SourceRange(TheCall->getArg(0)->getLocStart(), 320 TheCall->getArg(1)->getLocEnd()); 321 return ExprError(); 322 } 323 324 unsigned numElements = FAType->getAsVectorType()->getNumElements(); 325 if (TheCall->getNumArgs() != numElements+2) { 326 if (TheCall->getNumArgs() < numElements+2) 327 return ExprError(Diag(TheCall->getLocEnd(), 328 diag::err_typecheck_call_too_few_args) 329 << 0 /*function call*/ << TheCall->getSourceRange()); 330 return ExprError(Diag(TheCall->getLocEnd(), 331 diag::err_typecheck_call_too_many_args) 332 << 0 /*function call*/ << TheCall->getSourceRange()); 333 } 334 335 for (unsigned i = 2; i < TheCall->getNumArgs(); i++) { 336 llvm::APSInt Result(32); 337 if (!TheCall->getArg(i)->isIntegerConstantExpr(Result, Context)) 338 return ExprError(Diag(TheCall->getLocStart(), 339 diag::err_shufflevector_nonconstant_argument) 340 << TheCall->getArg(i)->getSourceRange()); 341 342 if (Result.getActiveBits() > 64 || Result.getZExtValue() >= numElements*2) 343 return ExprError(Diag(TheCall->getLocStart(), 344 diag::err_shufflevector_argument_too_large) 345 << TheCall->getArg(i)->getSourceRange()); 346 } 347 348 llvm::SmallVector<Expr*, 32> exprs; 349 350 for (unsigned i = 0, e = TheCall->getNumArgs(); i != e; i++) { 351 exprs.push_back(TheCall->getArg(i)); 352 TheCall->setArg(i, 0); 353 } 354 355 return Owned(new (Context) ShuffleVectorExpr(exprs.begin(), numElements+2, 356 FAType, 357 TheCall->getCallee()->getLocStart(), 358 TheCall->getRParenLoc())); 359} 360 361/// SemaBuiltinPrefetch - Handle __builtin_prefetch. 362// This is declared to take (const void*, ...) and can take two 363// optional constant int args. 364bool Sema::SemaBuiltinPrefetch(CallExpr *TheCall) { 365 unsigned NumArgs = TheCall->getNumArgs(); 366 367 if (NumArgs > 3) 368 return Diag(TheCall->getLocEnd(), diag::err_typecheck_call_too_many_args) 369 << 0 /*function call*/ << TheCall->getSourceRange(); 370 371 // Argument 0 is checked for us and the remaining arguments must be 372 // constant integers. 373 for (unsigned i = 1; i != NumArgs; ++i) { 374 Expr *Arg = TheCall->getArg(i); 375 QualType RWType = Arg->getType(); 376 377 const BuiltinType *BT = RWType->getAsBuiltinType(); 378 llvm::APSInt Result; 379 if (!BT || BT->getKind() != BuiltinType::Int || 380 !Arg->isIntegerConstantExpr(Result, Context)) 381 return Diag(TheCall->getLocStart(), diag::err_prefetch_invalid_argument) 382 << SourceRange(Arg->getLocStart(), Arg->getLocEnd()); 383 384 // FIXME: gcc issues a warning and rewrites these to 0. These 385 // seems especially odd for the third argument since the default 386 // is 3. 387 if (i == 1) { 388 if (Result.getSExtValue() < 0 || Result.getSExtValue() > 1) 389 return Diag(TheCall->getLocStart(), diag::err_argument_invalid_range) 390 << "0" << "1" << SourceRange(Arg->getLocStart(), Arg->getLocEnd()); 391 } else { 392 if (Result.getSExtValue() < 0 || Result.getSExtValue() > 3) 393 return Diag(TheCall->getLocStart(), diag::err_argument_invalid_range) 394 << "0" << "3" << SourceRange(Arg->getLocStart(), Arg->getLocEnd()); 395 } 396 } 397 398 return false; 399} 400 401/// SemaBuiltinObjectSize - Handle __builtin_object_size(void *ptr, 402/// int type). This simply type checks that type is one of the defined 403/// constants (0-3). 404bool Sema::SemaBuiltinObjectSize(CallExpr *TheCall) { 405 Expr *Arg = TheCall->getArg(1); 406 QualType ArgType = Arg->getType(); 407 const BuiltinType *BT = ArgType->getAsBuiltinType(); 408 llvm::APSInt Result(32); 409 if (!BT || BT->getKind() != BuiltinType::Int || 410 !Arg->isIntegerConstantExpr(Result, Context)) { 411 return Diag(TheCall->getLocStart(), diag::err_object_size_invalid_argument) 412 << SourceRange(Arg->getLocStart(), Arg->getLocEnd()); 413 } 414 415 if (Result.getSExtValue() < 0 || Result.getSExtValue() > 3) { 416 return Diag(TheCall->getLocStart(), diag::err_argument_invalid_range) 417 << "0" << "3" << SourceRange(Arg->getLocStart(), Arg->getLocEnd()); 418 } 419 420 return false; 421} 422 423// Handle i > 1 ? "x" : "y", recursivelly 424bool Sema::SemaCheckStringLiteral(Expr *E, CallExpr *TheCall, bool HasVAListArg, 425 unsigned format_idx, unsigned firstDataArg) { 426 427 switch (E->getStmtClass()) { 428 case Stmt::ConditionalOperatorClass: { 429 ConditionalOperator *C = cast<ConditionalOperator>(E); 430 return SemaCheckStringLiteral(C->getLHS(), TheCall, 431 HasVAListArg, format_idx, firstDataArg) 432 && SemaCheckStringLiteral(C->getRHS(), TheCall, 433 HasVAListArg, format_idx, firstDataArg); 434 } 435 436 case Stmt::ImplicitCastExprClass: { 437 ImplicitCastExpr *Expr = dyn_cast<ImplicitCastExpr>(E); 438 return SemaCheckStringLiteral(Expr->getSubExpr(), TheCall, HasVAListArg, 439 format_idx, firstDataArg); 440 } 441 442 case Stmt::ParenExprClass: { 443 ParenExpr *Expr = dyn_cast<ParenExpr>(E); 444 return SemaCheckStringLiteral(Expr->getSubExpr(), TheCall, HasVAListArg, 445 format_idx, firstDataArg); 446 } 447 448 default: { 449 ObjCStringLiteral *ObjCFExpr = dyn_cast<ObjCStringLiteral>(E); 450 StringLiteral *StrE = NULL; 451 452 if (ObjCFExpr) 453 StrE = ObjCFExpr->getString(); 454 else 455 StrE = dyn_cast<StringLiteral>(E); 456 457 if (StrE) { 458 CheckPrintfString(StrE, E, TheCall, HasVAListArg, format_idx, 459 firstDataArg); 460 return true; 461 } 462 463 return false; 464 } 465 } 466} 467 468 469/// CheckPrintfArguments - Check calls to printf (and similar functions) for 470/// correct use of format strings. 471/// 472/// HasVAListArg - A predicate indicating whether the printf-like 473/// function is passed an explicit va_arg argument (e.g., vprintf) 474/// 475/// format_idx - The index into Args for the format string. 476/// 477/// Improper format strings to functions in the printf family can be 478/// the source of bizarre bugs and very serious security holes. A 479/// good source of information is available in the following paper 480/// (which includes additional references): 481/// 482/// FormatGuard: Automatic Protection From printf Format String 483/// Vulnerabilities, Proceedings of the 10th USENIX Security Symposium, 2001. 484/// 485/// Functionality implemented: 486/// 487/// We can statically check the following properties for string 488/// literal format strings for non v.*printf functions (where the 489/// arguments are passed directly): 490// 491/// (1) Are the number of format conversions equal to the number of 492/// data arguments? 493/// 494/// (2) Does each format conversion correctly match the type of the 495/// corresponding data argument? (TODO) 496/// 497/// Moreover, for all printf functions we can: 498/// 499/// (3) Check for a missing format string (when not caught by type checking). 500/// 501/// (4) Check for no-operation flags; e.g. using "#" with format 502/// conversion 'c' (TODO) 503/// 504/// (5) Check the use of '%n', a major source of security holes. 505/// 506/// (6) Check for malformed format conversions that don't specify anything. 507/// 508/// (7) Check for empty format strings. e.g: printf(""); 509/// 510/// (8) Check that the format string is a wide literal. 511/// 512/// (9) Also check the arguments of functions with the __format__ attribute. 513/// (TODO). 514/// 515/// All of these checks can be done by parsing the format string. 516/// 517/// For now, we ONLY do (1), (3), (5), (6), (7), and (8). 518void 519Sema::CheckPrintfArguments(CallExpr *TheCall, bool HasVAListArg, 520 unsigned format_idx, unsigned firstDataArg) { 521 Expr *Fn = TheCall->getCallee(); 522 523 // CHECK: printf-like function is called with no format string. 524 if (format_idx >= TheCall->getNumArgs()) { 525 Diag(TheCall->getRParenLoc(), diag::warn_printf_missing_format_string) 526 << Fn->getSourceRange(); 527 return; 528 } 529 530 Expr *OrigFormatExpr = TheCall->getArg(format_idx)->IgnoreParenCasts(); 531 532 // CHECK: format string is not a string literal. 533 // 534 // Dynamically generated format strings are difficult to 535 // automatically vet at compile time. Requiring that format strings 536 // are string literals: (1) permits the checking of format strings by 537 // the compiler and thereby (2) can practically remove the source of 538 // many format string exploits. 539 540 // Format string can be either ObjC string (e.g. @"%d") or 541 // C string (e.g. "%d") 542 // ObjC string uses the same format specifiers as C string, so we can use 543 // the same format string checking logic for both ObjC and C strings. 544 bool isFExpr = SemaCheckStringLiteral(OrigFormatExpr, TheCall, 545 HasVAListArg, format_idx, 546 firstDataArg); 547 548 if (!isFExpr) { 549 // For vprintf* functions (i.e., HasVAListArg==true), we add a 550 // special check to see if the format string is a function parameter 551 // of the function calling the printf function. If the function 552 // has an attribute indicating it is a printf-like function, then we 553 // should suppress warnings concerning non-literals being used in a call 554 // to a vprintf function. For example: 555 // 556 // void 557 // logmessage(char const *fmt __attribute__ (format (printf, 1, 2)), ...) { 558 // va_list ap; 559 // va_start(ap, fmt); 560 // vprintf(fmt, ap); // Do NOT emit a warning about "fmt". 561 // ... 562 // 563 // 564 // FIXME: We don't have full attribute support yet, so just check to see 565 // if the argument is a DeclRefExpr that references a parameter. We'll 566 // add proper support for checking the attribute later. 567 if (HasVAListArg) 568 if (DeclRefExpr* DR = dyn_cast<DeclRefExpr>(OrigFormatExpr)) 569 if (isa<ParmVarDecl>(DR->getDecl())) 570 return; 571 572 Diag(TheCall->getArg(format_idx)->getLocStart(), 573 diag::warn_printf_not_string_constant) 574 << OrigFormatExpr->getSourceRange(); 575 return; 576 } 577} 578 579void Sema::CheckPrintfString(StringLiteral *FExpr, Expr *OrigFormatExpr, 580 CallExpr *TheCall, bool HasVAListArg, unsigned format_idx, 581 unsigned firstDataArg) { 582 583 ObjCStringLiteral *ObjCFExpr = dyn_cast<ObjCStringLiteral>(OrigFormatExpr); 584 // CHECK: is the format string a wide literal? 585 if (FExpr->isWide()) { 586 Diag(FExpr->getLocStart(), 587 diag::warn_printf_format_string_is_wide_literal) 588 << OrigFormatExpr->getSourceRange(); 589 return; 590 } 591 592 // Str - The format string. NOTE: this is NOT null-terminated! 593 const char * const Str = FExpr->getStrData(); 594 595 // CHECK: empty format string? 596 const unsigned StrLen = FExpr->getByteLength(); 597 598 if (StrLen == 0) { 599 Diag(FExpr->getLocStart(), diag::warn_printf_empty_format_string) 600 << OrigFormatExpr->getSourceRange(); 601 return; 602 } 603 604 // We process the format string using a binary state machine. The 605 // current state is stored in CurrentState. 606 enum { 607 state_OrdChr, 608 state_Conversion 609 } CurrentState = state_OrdChr; 610 611 // numConversions - The number of conversions seen so far. This is 612 // incremented as we traverse the format string. 613 unsigned numConversions = 0; 614 615 // numDataArgs - The number of data arguments after the format 616 // string. This can only be determined for non vprintf-like 617 // functions. For those functions, this value is 1 (the sole 618 // va_arg argument). 619 unsigned numDataArgs = TheCall->getNumArgs()-firstDataArg; 620 621 // Inspect the format string. 622 unsigned StrIdx = 0; 623 624 // LastConversionIdx - Index within the format string where we last saw 625 // a '%' character that starts a new format conversion. 626 unsigned LastConversionIdx = 0; 627 628 for (; StrIdx < StrLen; ++StrIdx) { 629 630 // Is the number of detected conversion conversions greater than 631 // the number of matching data arguments? If so, stop. 632 if (!HasVAListArg && numConversions > numDataArgs) break; 633 634 // Handle "\0" 635 if (Str[StrIdx] == '\0') { 636 // The string returned by getStrData() is not null-terminated, 637 // so the presence of a null character is likely an error. 638 Diag(getLocationOfStringLiteralByte(FExpr, StrIdx), 639 diag::warn_printf_format_string_contains_null_char) 640 << OrigFormatExpr->getSourceRange(); 641 return; 642 } 643 644 // Ordinary characters (not processing a format conversion). 645 if (CurrentState == state_OrdChr) { 646 if (Str[StrIdx] == '%') { 647 CurrentState = state_Conversion; 648 LastConversionIdx = StrIdx; 649 } 650 continue; 651 } 652 653 // Seen '%'. Now processing a format conversion. 654 switch (Str[StrIdx]) { 655 // Handle dynamic precision or width specifier. 656 case '*': { 657 ++numConversions; 658 659 if (!HasVAListArg && numConversions > numDataArgs) { 660 SourceLocation Loc = getLocationOfStringLiteralByte(FExpr, StrIdx); 661 662 if (Str[StrIdx-1] == '.') 663 Diag(Loc, diag::warn_printf_asterisk_precision_missing_arg) 664 << OrigFormatExpr->getSourceRange(); 665 else 666 Diag(Loc, diag::warn_printf_asterisk_width_missing_arg) 667 << OrigFormatExpr->getSourceRange(); 668 669 // Don't do any more checking. We'll just emit spurious errors. 670 return; 671 } 672 673 // Perform type checking on width/precision specifier. 674 Expr *E = TheCall->getArg(format_idx+numConversions); 675 if (const BuiltinType *BT = E->getType()->getAsBuiltinType()) 676 if (BT->getKind() == BuiltinType::Int) 677 break; 678 679 SourceLocation Loc = getLocationOfStringLiteralByte(FExpr, StrIdx); 680 681 if (Str[StrIdx-1] == '.') 682 Diag(Loc, diag::warn_printf_asterisk_precision_wrong_type) 683 << E->getType() << E->getSourceRange(); 684 else 685 Diag(Loc, diag::warn_printf_asterisk_width_wrong_type) 686 << E->getType() << E->getSourceRange(); 687 688 break; 689 } 690 691 // Characters which can terminate a format conversion 692 // (e.g. "%d"). Characters that specify length modifiers or 693 // other flags are handled by the default case below. 694 // 695 // FIXME: additional checks will go into the following cases. 696 case 'i': 697 case 'd': 698 case 'o': 699 case 'u': 700 case 'x': 701 case 'X': 702 case 'D': 703 case 'O': 704 case 'U': 705 case 'e': 706 case 'E': 707 case 'f': 708 case 'F': 709 case 'g': 710 case 'G': 711 case 'a': 712 case 'A': 713 case 'c': 714 case 'C': 715 case 'S': 716 case 's': 717 case 'p': 718 ++numConversions; 719 CurrentState = state_OrdChr; 720 break; 721 722 // CHECK: Are we using "%n"? Issue a warning. 723 case 'n': { 724 ++numConversions; 725 CurrentState = state_OrdChr; 726 SourceLocation Loc = getLocationOfStringLiteralByte(FExpr, 727 LastConversionIdx); 728 729 Diag(Loc, diag::warn_printf_write_back)<<OrigFormatExpr->getSourceRange(); 730 break; 731 } 732 733 // Handle "%@" 734 case '@': 735 // %@ is allowed in ObjC format strings only. 736 if(ObjCFExpr != NULL) 737 CurrentState = state_OrdChr; 738 else { 739 // Issue a warning: invalid format conversion. 740 SourceLocation Loc = 741 getLocationOfStringLiteralByte(FExpr, LastConversionIdx); 742 743 Diag(Loc, diag::warn_printf_invalid_conversion) 744 << std::string(Str+LastConversionIdx, 745 Str+std::min(LastConversionIdx+2, StrLen)) 746 << OrigFormatExpr->getSourceRange(); 747 } 748 ++numConversions; 749 break; 750 751 // Handle "%%" 752 case '%': 753 // Sanity check: Was the first "%" character the previous one? 754 // If not, we will assume that we have a malformed format 755 // conversion, and that the current "%" character is the start 756 // of a new conversion. 757 if (StrIdx - LastConversionIdx == 1) 758 CurrentState = state_OrdChr; 759 else { 760 // Issue a warning: invalid format conversion. 761 SourceLocation Loc = 762 getLocationOfStringLiteralByte(FExpr, LastConversionIdx); 763 764 Diag(Loc, diag::warn_printf_invalid_conversion) 765 << std::string(Str+LastConversionIdx, Str+StrIdx) 766 << OrigFormatExpr->getSourceRange(); 767 768 // This conversion is broken. Advance to the next format 769 // conversion. 770 LastConversionIdx = StrIdx; 771 ++numConversions; 772 } 773 break; 774 775 default: 776 // This case catches all other characters: flags, widths, etc. 777 // We should eventually process those as well. 778 break; 779 } 780 } 781 782 if (CurrentState == state_Conversion) { 783 // Issue a warning: invalid format conversion. 784 SourceLocation Loc = 785 getLocationOfStringLiteralByte(FExpr, LastConversionIdx); 786 787 Diag(Loc, diag::warn_printf_invalid_conversion) 788 << std::string(Str+LastConversionIdx, 789 Str+std::min(LastConversionIdx+2, StrLen)) 790 << OrigFormatExpr->getSourceRange(); 791 return; 792 } 793 794 if (!HasVAListArg) { 795 // CHECK: Does the number of format conversions exceed the number 796 // of data arguments? 797 if (numConversions > numDataArgs) { 798 SourceLocation Loc = 799 getLocationOfStringLiteralByte(FExpr, LastConversionIdx); 800 801 Diag(Loc, diag::warn_printf_insufficient_data_args) 802 << OrigFormatExpr->getSourceRange(); 803 } 804 // CHECK: Does the number of data arguments exceed the number of 805 // format conversions in the format string? 806 else if (numConversions < numDataArgs) 807 Diag(TheCall->getArg(format_idx+numConversions+1)->getLocStart(), 808 diag::warn_printf_too_many_data_args) 809 << OrigFormatExpr->getSourceRange(); 810 } 811} 812 813//===--- CHECK: Return Address of Stack Variable --------------------------===// 814 815static DeclRefExpr* EvalVal(Expr *E); 816static DeclRefExpr* EvalAddr(Expr* E); 817 818/// CheckReturnStackAddr - Check if a return statement returns the address 819/// of a stack variable. 820void 821Sema::CheckReturnStackAddr(Expr *RetValExp, QualType lhsType, 822 SourceLocation ReturnLoc) { 823 824 // Perform checking for returned stack addresses. 825 if (lhsType->isPointerType() || lhsType->isBlockPointerType()) { 826 if (DeclRefExpr *DR = EvalAddr(RetValExp)) 827 Diag(DR->getLocStart(), diag::warn_ret_stack_addr) 828 << DR->getDecl()->getDeclName() << RetValExp->getSourceRange(); 829 830 // Skip over implicit cast expressions when checking for block expressions. 831 if (ImplicitCastExpr *IcExpr = 832 dyn_cast_or_null<ImplicitCastExpr>(RetValExp)) 833 RetValExp = IcExpr->getSubExpr(); 834 835 if (BlockExpr *C = dyn_cast_or_null<BlockExpr>(RetValExp)) 836 Diag(C->getLocStart(), diag::err_ret_local_block) 837 << C->getSourceRange(); 838 } 839 // Perform checking for stack values returned by reference. 840 else if (lhsType->isReferenceType()) { 841 // Check for a reference to the stack 842 if (DeclRefExpr *DR = EvalVal(RetValExp)) 843 Diag(DR->getLocStart(), diag::warn_ret_stack_ref) 844 << DR->getDecl()->getDeclName() << RetValExp->getSourceRange(); 845 } 846} 847 848/// EvalAddr - EvalAddr and EvalVal are mutually recursive functions that 849/// check if the expression in a return statement evaluates to an address 850/// to a location on the stack. The recursion is used to traverse the 851/// AST of the return expression, with recursion backtracking when we 852/// encounter a subexpression that (1) clearly does not lead to the address 853/// of a stack variable or (2) is something we cannot determine leads to 854/// the address of a stack variable based on such local checking. 855/// 856/// EvalAddr processes expressions that are pointers that are used as 857/// references (and not L-values). EvalVal handles all other values. 858/// At the base case of the recursion is a check for a DeclRefExpr* in 859/// the refers to a stack variable. 860/// 861/// This implementation handles: 862/// 863/// * pointer-to-pointer casts 864/// * implicit conversions from array references to pointers 865/// * taking the address of fields 866/// * arbitrary interplay between "&" and "*" operators 867/// * pointer arithmetic from an address of a stack variable 868/// * taking the address of an array element where the array is on the stack 869static DeclRefExpr* EvalAddr(Expr *E) { 870 // We should only be called for evaluating pointer expressions. 871 assert((E->getType()->isPointerType() || 872 E->getType()->isBlockPointerType() || 873 E->getType()->isObjCQualifiedIdType()) && 874 "EvalAddr only works on pointers"); 875 876 // Our "symbolic interpreter" is just a dispatch off the currently 877 // viewed AST node. We then recursively traverse the AST by calling 878 // EvalAddr and EvalVal appropriately. 879 switch (E->getStmtClass()) { 880 case Stmt::ParenExprClass: 881 // Ignore parentheses. 882 return EvalAddr(cast<ParenExpr>(E)->getSubExpr()); 883 884 case Stmt::UnaryOperatorClass: { 885 // The only unary operator that make sense to handle here 886 // is AddrOf. All others don't make sense as pointers. 887 UnaryOperator *U = cast<UnaryOperator>(E); 888 889 if (U->getOpcode() == UnaryOperator::AddrOf) 890 return EvalVal(U->getSubExpr()); 891 else 892 return NULL; 893 } 894 895 case Stmt::BinaryOperatorClass: { 896 // Handle pointer arithmetic. All other binary operators are not valid 897 // in this context. 898 BinaryOperator *B = cast<BinaryOperator>(E); 899 BinaryOperator::Opcode op = B->getOpcode(); 900 901 if (op != BinaryOperator::Add && op != BinaryOperator::Sub) 902 return NULL; 903 904 Expr *Base = B->getLHS(); 905 906 // Determine which argument is the real pointer base. It could be 907 // the RHS argument instead of the LHS. 908 if (!Base->getType()->isPointerType()) Base = B->getRHS(); 909 910 assert (Base->getType()->isPointerType()); 911 return EvalAddr(Base); 912 } 913 914 // For conditional operators we need to see if either the LHS or RHS are 915 // valid DeclRefExpr*s. If one of them is valid, we return it. 916 case Stmt::ConditionalOperatorClass: { 917 ConditionalOperator *C = cast<ConditionalOperator>(E); 918 919 // Handle the GNU extension for missing LHS. 920 if (Expr *lhsExpr = C->getLHS()) 921 if (DeclRefExpr* LHS = EvalAddr(lhsExpr)) 922 return LHS; 923 924 return EvalAddr(C->getRHS()); 925 } 926 927 // For casts, we need to handle conversions from arrays to 928 // pointer values, and pointer-to-pointer conversions. 929 case Stmt::ImplicitCastExprClass: 930 case Stmt::CStyleCastExprClass: 931 case Stmt::CXXFunctionalCastExprClass: { 932 Expr* SubExpr = cast<CastExpr>(E)->getSubExpr(); 933 QualType T = SubExpr->getType(); 934 935 if (SubExpr->getType()->isPointerType() || 936 SubExpr->getType()->isBlockPointerType() || 937 SubExpr->getType()->isObjCQualifiedIdType()) 938 return EvalAddr(SubExpr); 939 else if (T->isArrayType()) 940 return EvalVal(SubExpr); 941 else 942 return 0; 943 } 944 945 // C++ casts. For dynamic casts, static casts, and const casts, we 946 // are always converting from a pointer-to-pointer, so we just blow 947 // through the cast. In the case the dynamic cast doesn't fail (and 948 // return NULL), we take the conservative route and report cases 949 // where we return the address of a stack variable. For Reinterpre 950 // FIXME: The comment about is wrong; we're not always converting 951 // from pointer to pointer. I'm guessing that this code should also 952 // handle references to objects. 953 case Stmt::CXXStaticCastExprClass: 954 case Stmt::CXXDynamicCastExprClass: 955 case Stmt::CXXConstCastExprClass: 956 case Stmt::CXXReinterpretCastExprClass: { 957 Expr *S = cast<CXXNamedCastExpr>(E)->getSubExpr(); 958 if (S->getType()->isPointerType() || S->getType()->isBlockPointerType()) 959 return EvalAddr(S); 960 else 961 return NULL; 962 } 963 964 // Everything else: we simply don't reason about them. 965 default: 966 return NULL; 967 } 968} 969 970 971/// EvalVal - This function is complements EvalAddr in the mutual recursion. 972/// See the comments for EvalAddr for more details. 973static DeclRefExpr* EvalVal(Expr *E) { 974 975 // We should only be called for evaluating non-pointer expressions, or 976 // expressions with a pointer type that are not used as references but instead 977 // are l-values (e.g., DeclRefExpr with a pointer type). 978 979 // Our "symbolic interpreter" is just a dispatch off the currently 980 // viewed AST node. We then recursively traverse the AST by calling 981 // EvalAddr and EvalVal appropriately. 982 switch (E->getStmtClass()) { 983 case Stmt::DeclRefExprClass: 984 case Stmt::QualifiedDeclRefExprClass: { 985 // DeclRefExpr: the base case. When we hit a DeclRefExpr we are looking 986 // at code that refers to a variable's name. We check if it has local 987 // storage within the function, and if so, return the expression. 988 DeclRefExpr *DR = cast<DeclRefExpr>(E); 989 990 if (VarDecl *V = dyn_cast<VarDecl>(DR->getDecl())) 991 if(V->hasLocalStorage() && !V->getType()->isReferenceType()) return DR; 992 993 return NULL; 994 } 995 996 case Stmt::ParenExprClass: 997 // Ignore parentheses. 998 return EvalVal(cast<ParenExpr>(E)->getSubExpr()); 999 1000 case Stmt::UnaryOperatorClass: { 1001 // The only unary operator that make sense to handle here 1002 // is Deref. All others don't resolve to a "name." This includes 1003 // handling all sorts of rvalues passed to a unary operator. 1004 UnaryOperator *U = cast<UnaryOperator>(E); 1005 1006 if (U->getOpcode() == UnaryOperator::Deref) 1007 return EvalAddr(U->getSubExpr()); 1008 1009 return NULL; 1010 } 1011 1012 case Stmt::ArraySubscriptExprClass: { 1013 // Array subscripts are potential references to data on the stack. We 1014 // retrieve the DeclRefExpr* for the array variable if it indeed 1015 // has local storage. 1016 return EvalAddr(cast<ArraySubscriptExpr>(E)->getBase()); 1017 } 1018 1019 case Stmt::ConditionalOperatorClass: { 1020 // For conditional operators we need to see if either the LHS or RHS are 1021 // non-NULL DeclRefExpr's. If one is non-NULL, we return it. 1022 ConditionalOperator *C = cast<ConditionalOperator>(E); 1023 1024 // Handle the GNU extension for missing LHS. 1025 if (Expr *lhsExpr = C->getLHS()) 1026 if (DeclRefExpr *LHS = EvalVal(lhsExpr)) 1027 return LHS; 1028 1029 return EvalVal(C->getRHS()); 1030 } 1031 1032 // Accesses to members are potential references to data on the stack. 1033 case Stmt::MemberExprClass: { 1034 MemberExpr *M = cast<MemberExpr>(E); 1035 1036 // Check for indirect access. We only want direct field accesses. 1037 if (!M->isArrow()) 1038 return EvalVal(M->getBase()); 1039 else 1040 return NULL; 1041 } 1042 1043 // Everything else: we simply don't reason about them. 1044 default: 1045 return NULL; 1046 } 1047} 1048 1049//===--- CHECK: Floating-Point comparisons (-Wfloat-equal) ---------------===// 1050 1051/// Check for comparisons of floating point operands using != and ==. 1052/// Issue a warning if these are no self-comparisons, as they are not likely 1053/// to do what the programmer intended. 1054void Sema::CheckFloatComparison(SourceLocation loc, Expr* lex, Expr *rex) { 1055 bool EmitWarning = true; 1056 1057 Expr* LeftExprSansParen = lex->IgnoreParens(); 1058 Expr* RightExprSansParen = rex->IgnoreParens(); 1059 1060 // Special case: check for x == x (which is OK). 1061 // Do not emit warnings for such cases. 1062 if (DeclRefExpr* DRL = dyn_cast<DeclRefExpr>(LeftExprSansParen)) 1063 if (DeclRefExpr* DRR = dyn_cast<DeclRefExpr>(RightExprSansParen)) 1064 if (DRL->getDecl() == DRR->getDecl()) 1065 EmitWarning = false; 1066 1067 1068 // Special case: check for comparisons against literals that can be exactly 1069 // represented by APFloat. In such cases, do not emit a warning. This 1070 // is a heuristic: often comparison against such literals are used to 1071 // detect if a value in a variable has not changed. This clearly can 1072 // lead to false negatives. 1073 if (EmitWarning) { 1074 if (FloatingLiteral* FLL = dyn_cast<FloatingLiteral>(LeftExprSansParen)) { 1075 if (FLL->isExact()) 1076 EmitWarning = false; 1077 } 1078 else 1079 if (FloatingLiteral* FLR = dyn_cast<FloatingLiteral>(RightExprSansParen)){ 1080 if (FLR->isExact()) 1081 EmitWarning = false; 1082 } 1083 } 1084 1085 // Check for comparisons with builtin types. 1086 if (EmitWarning) 1087 if (CallExpr* CL = dyn_cast<CallExpr>(LeftExprSansParen)) 1088 if (CL->isBuiltinCall(Context)) 1089 EmitWarning = false; 1090 1091 if (EmitWarning) 1092 if (CallExpr* CR = dyn_cast<CallExpr>(RightExprSansParen)) 1093 if (CR->isBuiltinCall(Context)) 1094 EmitWarning = false; 1095 1096 // Emit the diagnostic. 1097 if (EmitWarning) 1098 Diag(loc, diag::warn_floatingpoint_eq) 1099 << lex->getSourceRange() << rex->getSourceRange(); 1100} 1101