[cfe-dev] Fix for PR4701

[Daniel Dunbar]

David,

Have you had a chance to look at this crash yet? This is preventing us
from building various projects so I'd like to get it resolved soon.

 - Daniel

On Tue, Aug 18, 2009 at 10:39 PM, Daniel Dunbar<daniel at zuster.org> wrote:
> Ah, the problem appears to be related to the use of PCH:
> --
> ddunbar at giles:tmp$ cat t.h
> #include <Foundation/Foundation.h>
> ddunbar at giles:tmp$ cat t.m
> id f0(id x) {
>  return x->isa;
> }
> ddunbar at giles:tmp$ clang -x objective-c-header t.h
> ddunbar at giles:tmp$ clang -include t.h t.m
> 0   clang-cc          0x0000000101080755 PrintStackTrace(void*) + 38
> 1   clang-cc          0x0000000101080ce3 SignalHandler(int) + 336
> 2   libSystem.B.dylib 0x00007fff812ff83a _sigtramp + 26
> 3   libSystem.B.dylib 000000000000000000 _sigtramp + 2127562720
> 4   clang-cc          0x0000000100374eb1
> clang::ASTContext::getCanonicalType(clang::QualType) + 39
> 5   clang-cc          0x0000000100262463
> clang::Sema::ImpCastExprToType(clang::Expr*&, clang::QualType,
> clang::CastExpr::CastInfo const&, bool) + 123
> 6   clang-cc          0x00000001002d4635
> clang::Sema::ActOnMemberReferenceExpr(clang::Scope*,
> clang::ASTOwningResult<&(clang::ActionBase::DeleteExpr(void*))>,
> clang::SourceLocation, clang::tok::TokenKind, clang::SourceLocation,
> clang::IdentifierInfo&, clang::OpaquePtr<0>, clang::CXXScopeSpec
> const*) + 545
> 7   clang-cc          0x0000000100429172
> clang::Parser::ParsePostfixExpressionSuffix(clang::ASTOwningResult<&(clang::ActionBase::DeleteExpr(void*))>)
> + 2624
> 8   clang-cc          0x000000010042b587
> clang::Parser::ParseCastExpression(bool, bool, bool&, bool) + 3115
> 9   clang-cc          0x000000010042ceb7
> clang::Parser::ParseCastExpression(bool, bool, bool) + 99
> 10  clang-cc          0x000000010042818c
> clang::Parser::ParseAssignmentExpression() + 148
> 11  clang-cc          0x0000000100428616 clang::Parser::ParseExpression() + 42
> 12  clang-cc          0x0000000100442583
> clang::Parser::ParseReturnStatement() + 203
> 13  clang-cc          0x00000001004441cd
> clang::Parser::ParseStatementOrDeclaration(bool) + 2653
> 14  clang-cc          0x0000000100447a55
> clang::Parser::ParseCompoundStatementBody(bool) + 239
> 15  clang-cc          0x000000010044800b
> clang::Parser::ParseFunctionStatementBody(clang::OpaquePtr<0>) + 193
> 16  clang-cc          0x0000000100450e6d
> clang::Parser::ParseFunctionDefinition(clang::Declarator&,
> clang::Parser::ParsedTemplateInfo const&) + 1009
> 17  clang-cc          0x00000001004518d3
> clang::Parser::ParseDeclarationOrFunctionDefinition(clang::AccessSpecifier)
> + 1599
> 18  clang-cc          0x0000000100451ec2
> clang::Parser::ParseExternalDeclaration() + 1232
> 19  clang-cc          0x0000000100451f74
> clang::Parser::ParseTopLevelDecl(clang::OpaquePtr<1>&) + 106
> 20  clang-cc          0x0000000100260725
> clang::ParseAST(clang::Preprocessor&, clang::ASTConsumer*,
> clang::ASTContext&, bool, bool) + 497
> 21  clang-cc          0x0000000100030692
> ProcessInputFile(clang::Preprocessor&, clang::PreprocessorFactory&,
> std::string const&, ProgActions, llvm::StringMap<bool,
> llvm::MallocAllocator> const&, llvm::LLVMContext&) + 4175
> 22  clang-cc          0x000000010003203e main + 2909
> 23  clang-cc          0x000000010002c550 start + 52
> Stack dump:
> 0.      Program arguments:
> /Volumes/Data/Users/ddunbar/llvm/Debug/bin/clang-cc -triple
> x86_64-apple-darwin10 -S -disable-free -main-file-name t.m
> --relocation-model pic -pic-level=1 --disable-fp-elim
> --unwind-tables=1 --mcpu=core2 --fmath-errno=0
> -mmacosx-version-min=10.6.0 -include-pch t.h.gch
> -fdiagnostics-show-option -o
> /var/folders/DQ/DQ8GT3++HESEzT1obWBynE+++TI/-Tmp-/cc-YvJBuv.s -x
> objective-c t.m
> 1.      t.m:2:13: current parser token 'isa'
> 2.      t.m:1:13: parsing function body 'f0'
> 3.      t.m:1:13: in compound statement ('{}')
> clang: error: compiler command failed due to signal 11 (use -v to see
> invocation)
> --
>
> Probably the state about the redefinition isn't getting properly
> restored? I don't know much about the PCH implementation, myself...
>
>  - Daniel
>
>
> On Tue, Aug 18, 2009 at 8:57 AM, David Chisnall<csdavec at swansea.ac.uk> wrote:
>> On 18 Aug 2009, at 16:47, Daniel Dunbar wrote:
>>
>>> I think you missed the point here.
>>>
>>> If ObjCIdRedefinitionType has not been assigned, then it will be the
>>> null QualType. The comparison will succeed (since BaseType is not
>>> null), then BaseType will be assigned to the null type, then the code
>>> will crash a few lines later.
>>
>> Once again, can you provide a test case which demonstrates this?  I have
>> tests which attempt to access fields on an id-typed variable with no
>> definition of id provided, and they do not crash and do use this code path.
>>  If you can demonstrate a condition where this manifests as a bug, then I
>> would be more than happy to fix it.  As, at the moment, it is working as I
>> expect it to work, so I can't fix it because I am not seeing any breakage.
>>
>> The comparison is only there to avoid a redundant implicit cast when there
>> is one already (which can only happen in cases where a redefinition is
>> supplied).
>>
>> David
>>
>