[LLVMdev] Questions about llvm/Object/COFF.h

[Marshall Clow]

On Jun 11, 2012, at 7:39 PM, Sean Silva wrote:
> If you haven't already found it, you should look inside tools/llvm-objdump/llvm-objdump.cpp, which is an easy-to-follow example of how these APIs work

I had found that - and sadly, it doesn't do what I need to do.
In particular, I don't see how to get a coff_section from a section_iterator (and llvm-objdump doesn't do that, either)

At the moment, I want to read the section characteristics and the raw data.
I guess I can use the index-based calls rather than the iterator-based ones. (One-based? Really?)

Seems like a shame, though. Why have two different sets of functionality here?

Thanks, though.

-- Marshall


> 
> --Sean Silva.
> 
> On Mon, Jun 11, 2012 at 5:41 PM, Marshall Clow <mclow.lists at gmail.com> wrote:
> So, I'm trying to use this file to look inside COFF files.
> Got the header. OK.
> 
> Now I want to look at the sections.
> Look, there's a section iterator. I can use that!
> 
> So, I write:
>        for (llvm::object::section_iterator iter = Obj.begin_sections (); iter != Obj.end_sections(); ++iter )
> 
> and it doesn't compile. There's no ++ for section iterators.
> Apparently, you're supposed to write.
>        for (llvm::object::section_iterator iter = Obj.begin_sections (); iter != Obj.end_sections(); iter.increment(ec))
> Srsly?
> [ And - how do I go from a section_iterator to a coff_section ? ]
> 
> While I'm puzzling over that, I look some more, and I see:
>        error_code getSection(int32_t index, const coff_section *&Res) const;
> 
> Cool. (A bit weird; why a signed index?, but whatever)
> So I write:
>        const llvm::object::coff_section *sect;
>        for (std::size_t i = 0; i < NumSections; ++i)
>                Obj.getSection(i, sect);
> 
> And my program dies with a segmentation fault.
> Turns out that sect == NULL.
> More looking, I see that the sections are numbered 1 … N, not 0 ... N-1
> 
> Now I'm really really confused.  Why?
> 
> BTW - patch attached to add pre-increment to llvm::content_iterator (which is the template base for section_iterator, etc)
> 

-- Marshall

Marshall Clow     Idio Software   <mailto:mclow.lists at gmail.com>

A.D. 1517: Martin Luther nails his 95 Theses to the church door and is promptly moderated down to (-1, Flamebait).
        -- Yu Suzuki

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20120612/16ab42b8/attachment.html>