[lldb-dev] Problem with ClangExpressionDeclMap

[jingham at apple.com]

> On Jan 13, 2015, at 9:58 AM, Zachary Turner <zturner at google.com> wrote:
> 
> But then why does it work on Mac?
> 
> And why is this workaround needed at all, when you can just have it check the basename in the first place (e.g. in FindExternalVisibleDecls)?
> 
> I guess a higher level, more general question - Why is name lookup so complicated?  Clang already knows everything, why does LLDB need to modify the default behavior of Clang's name lookup?  I know LLDB can insert its own decls into the AST, but it seems like we can just get avoid returning those to the user, and still use clang for everything else.
> 

I don't get what you mean by this comment.  Name lookup in the debugger is pretty different from name lookup as it would be if we were sitting in the compiler trying to compile the expression as if it had been inserted in the current function at the PC.  The compiler can be quite strict about what is and isn't visible, whereas the debugger has to be as lax as possible.

For instance, suppose I am in a frame of a function that has a pointer to Foo, but that function is in a compile unit (and maybe even a shared library) that only contains a forward reference to Foo.  If you had another shared library that contains a definition of Foo, you would certainly want to be able to print *Foo.  Of course, from a strict compiler standpoint, this would be illegal, but telling debugger users that would not be a popular move.

Similarly, folks want to be able to use global variables (and eventually function statics when we work out a syntax for that) that aren't visible in the current function.

So the debugger has to get into the business of broadening name lookup to meet these needs.

Jim


> On Tue Jan 13 2015 at 2:54:15 AM Abid, Hafiz <Hafiz_Abid at mentor.com> wrote:
> In SymbolFileDWARF::FindFunctions (), there is code that runs only for Linux and BSD. That finds the function in global namespace.
> 
>  
> 
> Regards,
> 
> Abid
> 
>  
> 
> From: lldb-dev-bounces at cs.uiuc.edu [mailto:lldb-dev-bounces at cs.uiuc.edu] On Behalf Of Zachary Turner
> Sent: 12 January 2015 19:51
> To: lldb-dev at cs.uiuc.edu; Jim Ingham
> Subject: [lldb-dev] Problem with ClangExpressionDeclMap
> 
>  
> 
> Was looking into this bug on Windows, and I traced it down to an issue in ClangExpressionDeclMap.  ClangExpressionDeclMap::FindExternalVisibleDecls has a piece of code that looks like this:
> 
>  
> 
>             if (namespace_decl && module_sp)
> 
>             {
> 
>                 const bool include_symbols = false;
> 
>  
> 
>                 module_sp->FindFunctions(name,
> 
>                                          &namespace_decl,
> 
>                                          eFunctionNameTypeBase,
> 
>                                          include_symbols,
> 
>                                          include_inlines,
> 
>                                          append,
> 
>                                          sc_list);
> 
>             }
> 
>             else if (target && !namespace_decl)
> 
>             {
> 
>                 const bool include_symbols = true;
> 
>  
> 
>                 // TODO Fix FindFunctions so that it doesn't return
> 
>                 //   instance methods for eFunctionNameTypeBase.
> 
>  
> 
>                 target->GetImages().FindFunctions(name,
> 
>                                                   eFunctionNameTypeFull,
> 
>                                                   include_symbols,
> 
>                                                   include_inlines,
> 
>                                                   append,
> 
>                                                   sc_list);
> 
>             }
> 
>  
> 
> So it's only searching for the base name if the function is in a namespace, and if it's at global scope it's searching for the full name.
> 
>  
> 
> I'm not sure why this works on other platforms, but on Windows it doesn't work because if I have this code:
> 
>  
> 
> int foo(int x)
> 
> {
> 
> }
> 
>  
> 
> then the full name of this function is ?foo@@YAHH at Z
> 
>  
> 
> If I change eFunctionNameTypeFull to eFunctionNameTypeBase then everything works, and "p foo" finds the function.  So I've got a couple of questions:
> 
>  
> 
> 1) Why all this complicated logic?  I would expect that if I type "p foo" then it would just print everything whose base name is foo and is visible from within the current scope?  Am I underthinking this?  There's special cases for namespaces, global scope, instance methods, variables, functions, and it looks for things in certain orders, etc.  Is there any reason why it can't just find everything with a basename of foo visible within the current stack frame?
> 
>  
> 
> 2) I'm not sure what this comment means: 
> 
>                 // TODO Fix FindFunctions so that it doesn't return
> 
>                 //   instance methods for eFunctionNameTypeBase.
> 
> I changed it to eFunctionNameTypeBase and it fixes the original bug on Windows.  I inserted a class with an instance method named foo() and also a global method named foo(), and running "p foo" doesn't find the instance method, only the global method.  Is it possible this was somehow fixed, and it was forgotten to change this back to eFunctionNameTypeBase?
> 
>  
> 
> 3) Why does this work on other platforms?  full names are mangled on other platforms too, so I don't know how "p foo" doesn't run into this same issue on other platforms.  Any ideas?
> 
>  
> 
>  
> 
> Currently the best fix I have for this bug on Windows is to change eFunctionNameTypeFull to eFunctionNameTypeBase.  but I want to get some thoughts on that worrisome comment before I go forward with that patch.
>