[LLVMdev] Newbie question(?): How to correctly create debug info, when generating IR

[Eric Christopher]

Easiest way is to look at how clang generates debug info. See
clang/lib/CodeGen/CGDebugInfo.cpp.

-eric


On Fri, Dec 28, 2012 at 9:33 AM, Mario de Sousa <msousa at fe.up.pt> wrote:

>
>
>  Hello all,
>
>
> Summary & Context:
> -------------------------------
>  I am starting to write a front-end for some domain specific programming
> languages. Code generation seems to be working fine.
>
>  However, I am having trouble generating debug info, to be used by gdb.
>
>
>  The problem:
>  --------------------
>  I generate a foo.ll file, that is later compiled into an executable foo.
>
>  The foo.ll file I generate already contains metadata for datatypes,
> compile
> unit, subprograms, etc...
>
>  When debuging foo with ddd, I get the message that the file
>  <root_path>/sysdeps/i386/elf/start.S
>  does not exist. In other words, the debugger does not seem to know about
> the
> existence of foo.xx, the original source file.
>
>  I have compiled a small helloworld.c program, and compared the debug info
> in
> helloworld and foo, using 'readelf --debug-dump'.
>
>  I have noticed that in helloworld, the .debug_aranges section has 2
> address
> ranges,
>   - one pointing to a DW_TAG_compile_unit referencing the
> /sysdeps/i386/elf/start.S file
>   - the other pointing to a DW_TAG_compile_unit with the helloworld,c file.
>
>  However, in the foo program, the .debug_aranges section has only 1 address
> range, pointing to a DW_TAG_compile_unit referencing the
> /sysdeps/i386/elf/start.S file.
>  The second DW_TAG_compile_unit referencing the foo.xx file is present in
> the
> .debug_info section, but is not being referenced!
>
>  Strangely, some information that seems to be an address range referencing
> the
> foo.xx DW_TAG_compile_unit, is present in the .debug_pubtypes section. Why
> is
> this in the wrong section??
>
>
>
> The question:
> =========
>
>  Does anybody have any idea what it is I am doing wrong?
>
>  The issue seems to be related to generating the info for a CompileUnit.
> Currently, I am doing this:
>   dibuilder = new DIBuilder(themodule);
>   dibuilder->createCompileUnit(Lang,
>               StringRef("foo.xx")), /*finename*/
>               StringRef(".") /*Dir*/,
>               StringRef("XXX") /*Producer*/,
>               false /*isOptimized*/,
>               StringRef("") /*Flags*/,
>               0 /*RV: Runtime Version?*/);
>   DIFile file = dibuilder->createFile(StringRef("foo.x"), StringRef("."));
>   DICompileUnit compile_unit = DICompileUnit(file);
>   dibuilder->createFunction(compile_unit /*Scope*/,
>                  StringRef(function_name), StringRef(function_name),
>                  file,
>                  42 /* line number*/,
>                  di_func_type,
>                  false /*isLocalToUnit*/, true /*isDefinition*/,
>                  42 /*ScopeLine*/
>                 );
>   ...
>   ...
>   dibuilder->finalize();
>   module->dump();
>
>
>   To me, it seems wrong to create two compile units, one with
>   dibuilder->createCompileUnit()
> and the other directly
>   DICompileUnit compile_unit = DICompileUnit(file);
>
>  However, I could not figure out how to get a handle to the compile unit
> generated by   dibuilder->createCompileUnit(), in order to pass it to
> dibuilder->createFunction().
>
>
>
>
>    I can provide a lot more detail, but I do not want to bore you with
> this.
> If there is any info you need in order to help me out, please just ask,
> and I
> will do my best to provide it.
>
>
>
>   Cheers,
>
>           Mario.
> _______________________________________________
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>
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