[LLVMdev] dwarf directory table and file table

[Devang Patel]

Hi Nick,

On Aug 2, 2011, at 6:56 PM, Nick Lewycky wrote:

> I've been looking into the debug info in llvm recently. After conferring with a DWARF expert, I think what we really want for a file is to enter the actual name of the header that the preprocessor found between "" or <> on the #include line, and for the directory it should be the actual header search path used.

There are few wrinkles here, because these are preprocessor tokens.

- What about #include_next ?
- #include <Foo/Foo.h> does not mean  {include path ...}/Foo/Foo.h for Apple's framework header.
- Some IDEs, like Xcode, uses header maps. If you're curious search HeaderMaps in clang FE.

The dwarf line table should be able to encode directory names. I am not sure, what is the advantage of using actual tokens between "" or <> as a file name ? BTW, I do not know of any assembler directives like .directory

> I started by taking a look at how LLVM encodes this in a .s file and got pretty confused pretty quickly. For starters, we don't seem to ever emit any data directly into the .debug_line section directly. Is it filled in by the assembler based on the .file and .line directives? It seems like the assembler doesn't actually offer independent control of the directory and the file names? I guess I could invent new assembly directives, but it seems pretty surprising that I would need to! Have I gotten myself on the wrong track?
> 
> Nick
> 

-
Devang