[PATCH] Ensure __va_list_tag has default visibility

[Alp Toker]

On 09/07/2014 11:29, Alp Toker wrote:
>
> On 09/07/2014 09:55, Stephan Bergmann wrote:
>> ping
>>
>> On 06/25/2014 05:45 PM, Stephan Bergmann wrote:
>>> I stumbled across this on Linux with -fvisibility=hidden when
>>> -fsanitize=function reported a false positive for an indirect call to a
>>> function with a va_list (aka __builtin_va_list, aka __va_list_tag
>>> (*)[1]) parameter.  Because __va_list_tag was considered hidden, the
>>> RTTI for the function's type was not exported from the two shared
>>> libraries involved, so the equality check failed.
>>>
>>> This would apparently also need to be fixed in the other
>>> Create*BuiltinVaListDecl variants, but I'm not sure (a) whether the
>>> added const_cast is really deemed appropriate here (though I guess so,
>>> given the large number of existing similar const_casts across
>>> ASTContext.cpp), and (b) what the preferred way would be to break that
>>> long line. ;)
>
> Hi Stephan,
>
> I wrote the buildImplicitRecord() utility, and in principle the 
> attribute could be added centrally to that function -- if these are 
> the semantics we want for most built-in types, as you suggest, it 
> makes sense to centralize the decision.
>
> Another option would be to calculate the special linkage in 
> computeLVForDecl() instead of using an attribute, but it doesn't 
> really matter either way I think as the result is the same.
>
> The bigger question is whether (1) default visibility is correct for 
> all built-in types currently being generated by buildImplicitRecord() 
> and (2) whether this is a valid choice for all targets we support 
> including MSVC drop-in compatibility mode.
>
> To help answer question (1), the affected built-in types would be:
>
> lib/AST/ASTContext.cpp:    Float128StubDecl = 
> buildImplicitRecord("__float128");
> lib/AST/ASTContext.cpp:    CFConstantStringTypeDecl = 
> buildImplicitRecord("NSConstantString");
> lib/AST/ASTContext.cpp:    RecordDecl *ObjCSuperTypeDecl = 
> buildImplicitRecord("objc_super");
> lib/AST/ASTContext.cpp:  RD = buildImplicitRecord("__block_descriptor");
> lib/AST/ASTContext.cpp:  RD = 
> buildImplicitRecord("__block_descriptor_withcopydispose");
> lib/AST/ASTContext.cpp:  RecordDecl *VaListTagDecl = 
> Context->buildImplicitRecord("__va_list");
> lib/AST/ASTContext.cpp:  VaListTagDecl = 
> Context->buildImplicitRecord("__va_list_tag");
> lib/AST/ASTContext.cpp:  VaListTagDecl = 
> Context->buildImplicitRecord("__va_list_tag");
> lib/AST/ASTContext.cpp:  RecordDecl *VaListDecl = 
> Context->buildImplicitRecord("__va_list");
> lib/AST/ASTContext.cpp:  VaListTagDecl = 
> Context->buildImplicitRecord("__va_list_tag");
> lib/CodeGen/CodeGenModule.cpp:    RecordDecl *D = 
> Context.buildImplicitRecord("__builtin_NSString");
> lib/CodeGen/CodeGenModule.cpp:    RecordDecl *D = 
> Context.buildImplicitRecord("__objcFastEnumerationState");
> lib/Sema/Sema.cpp: 
> PushOnScopeChains(Context.buildImplicitRecord("type_info", TTK_Class),
>

There are also the implicit typedefs -- I don't know what the 
visibility/export deal is for those:


lib/AST/ASTContext.cpp:    Int128Decl = buildImplicitTypedef(Int128Ty, 
"__int128_t");
lib/AST/ASTContext.cpp:    UInt128Decl = 
buildImplicitTypedef(UnsignedInt128Ty, "__uint128_t");
lib/AST/ASTContext.cpp:        buildImplicitTypedef(getObjCIdType(), 
"instancetype");
lib/AST/ASTContext.cpp:    ObjCIdDecl = buildImplicitTypedef(T, "id");
lib/AST/ASTContext.cpp:    ObjCSelDecl = buildImplicitTypedef(T, "SEL");
lib/AST/ASTContext.cpp:    ObjCClassDecl = buildImplicitTypedef(T, "Class");
lib/AST/ASTContext.cpp:  return Context->buildImplicitTypedef(T, 
"__builtin_va_list");
lib/AST/ASTContext.cpp:  return Context->buildImplicitTypedef(T, 
"__builtin_va_list");
lib/AST/ASTContext.cpp:  return 
Context->buildImplicitTypedef(VaListTagType, "__builtin_va_list");
lib/AST/ASTContext.cpp: Context->buildImplicitTypedef(VaListTagType, 
"__va_list_tag");
lib/AST/ASTContext.cpp:  return 
Context->buildImplicitTypedef(VaListTagArrayType, "__builtin_va_list");
lib/AST/ASTContext.cpp: Context->buildImplicitTypedef(VaListTagType, 
"__va_list_tag");
lib/AST/ASTContext.cpp:  return 
Context->buildImplicitTypedef(VaListTagArrayType, "__builtin_va_list");
lib/AST/ASTContext.cpp:  return 
Context->buildImplicitTypedef(IntArrayType, "__builtin_va_list");
lib/AST/ASTContext.cpp:  return Context->buildImplicitTypedef(T, 
"__builtin_va_list");
lib/AST/ASTContext.cpp: Context->buildImplicitTypedef(VaListTagType, 
"__va_list_tag");
lib/AST/ASTContext.cpp:  return 
Context->buildImplicitTypedef(VaListTagArrayType, "__builtin_va_list");
lib/Sema/Sema.cpp: PushOnScopeChains(Context.buildImplicitTypedef(T, 
Name), TUScope);

Alp.


> I'll need help answering those questions from linkage/visibility folks 
> on the list before going forward with a change like this.
>
> Thanks
> Alp.
>
>
>
>>>
>>> Stephan
>>
>>
>>
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>

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