adding custom attributes

Clang Frontend
1

Hi there,

I'm new to clang and LLVM. I want to extend clang to handle
non-standard variable attributes. What would be the best approach to
that? Any help would be appreciated.

Thanks very much,

Naoya

2

I'm new to clang and LLVM. I want to extend clang to handle
non-standard variable attributes. What would be the best approach to
that? Any help would be appreciated.

Depending on what you want to do, for now I assume that you are trying to do something like:

int x __attribute__((foo));

And then have the foo attribute apply to the declaration.

The interesting files for this are:

include/Parser/AttributeList.h: Define an enum entry AT_foo
lib/Parser/AttributeList.cpp: Add a memcmp call and return in order to allow the decoding of the attribute at the appropriate point; in the case of foo that would be under case 3.

If you want your attribute to apply to the declaration, check the function ProcessDeclAttribute in lib/Sema/SemaDeclAttr.cpp, most of the handler called by that function do 2 things, they check the context of the attribute and the number of argument, and they insert the attribute in the declaration's attribute list, the declaration attributes need to inherit from the Attr class, you can find this in include/AST/Attr.h where a number of standard attribute classes are defined with the DEF_SIMPLE_ATTR macro, that macro will generate an attribute class that is good enough for simple boolean attributes.

Your AST consumer can then read the attributes associated with the declaration in a later stage (check the clang Doxygen docs for how to do this).

If you are trying to add the attributes to types and not the actual declarations, then it is a bit more tricky and you should check the thread that I started called "adding attribute bits to types".

Regards,
Mattias

3

Thank you Mattias. Yes, I'm currently only interested in adding
attributes to variables not types. I'll look into those files.

Naoya