[PATCH] D126864: [clang] Introduce -fstrict-flex-arrays=<n> for stricter handling of flexible arrays

[Stephan Bergmann via Phabricator via cfe-commits]

sberg added a comment.

In D126864#3612149 <https://reviews.llvm.org/D126864#3612149>, @sberg wrote:

> see https://reviews.llvm.org/D128643 "[clang] -fsanitize=array-bounds: treat all trailing size-1 arrays as flexible" for another regression

For the record (now that the original commit has been reverted anyway for now):

Besides the above regression for `-fsanitize=array-bounds` and macro'ized array size in HarfBuzz, I also ran into yet another regression when Firebird is built with `-fsanitize=array-bounds`:  That project, in https://github.com/FirebirdSQL/firebird/blob/master/src/lock/lock_proto.h uses a trailing member

  	srq lhb_hash[1];			// Hash table

as a flexible array, but declared in a

  struct lhb : public Firebird::MemoryHeader

that is not a standard-layout class (because the `Firebird::MemoryHeader` base class also declares non-static data members).  And `isFlexibleArrayMember` returns `false` if the surrounding class is not a standard-layout class.

In the end, what brought back a successful `-fsanitize=array-bounds` LibreOffice (which bundles those HarfBuzz and Firebird, among others) for me was to exclude the whole set of blocks

  // Don't consider sizes resulting from macro expansions or template argument
  // substitution to form C89 tail-padded arrays.
  
  TypeSourceInfo *TInfo = FD->getTypeSourceInfo();
  while (TInfo) {
    TypeLoc TL = TInfo->getTypeLoc();
    // Look through typedefs.
    if (TypedefTypeLoc TTL = TL.getAs<TypedefTypeLoc>()) {
      const TypedefNameDecl *TDL = TTL.getTypedefNameDecl();
      TInfo = TDL->getTypeSourceInfo();
      continue;
    }
    if (ConstantArrayTypeLoc CTL = TL.getAs<ConstantArrayTypeLoc>()) {
      const Expr *SizeExpr = dyn_cast<IntegerLiteral>(CTL.getSizeExpr());
      if (!SizeExpr || SizeExpr->getExprLoc().isMacroID())
        return false;
    }
    break;
  }
  
  const ObjCInterfaceDecl *ID =
      dyn_cast<ObjCInterfaceDecl>(FD->getDeclContext());
  const RecordDecl *RD = dyn_cast<RecordDecl>(FD->getDeclContext());
  if (RD) {
    if (RD->isUnion())
      return false;
    if (const CXXRecordDecl *CRD = dyn_cast<CXXRecordDecl>(RD)) {
      if (!CRD->isStandardLayout())
        return false;
    }
  } else if (!ID)
    return false;

(by means of an additional `bool` parameter) when `isFlexibleArrayMember` is called from `getArrayIndexingBound` (in `clang/lib/CodeGen/CGExpr.cpp`).


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D126864/new/

https://reviews.llvm.org/D126864