create relocation entry from scratch

create relocation entry from scratch

[peter matula]

Hello,

I'm using BFD to transform our internal binary format to ELF. I have 
already successfully made transformation of executable files which can 
be described like this:

CreateBfd();    // create BFD file
GetArch();    // convert arch and mach info from our format to BFD
CreateSections();    // create sections in BFD
GetSymtab();    // create and fill symbol table
GetSectionData();    // copy data from out format to BFD
CloeBfd();    // write and close BFD

Now i would like to add relocation conversion. Until now everything went 
well but i stuck on this. When should I add relocations ? During section 
creation in CreateSections(), after GetSymTab() or somewhen else ?
And how should i create relocation entry from scratch ? I found few 
examples like this:

relpp = (arelent **) xmalloc(get_reloc_upper_bound(ibfd, isec));
relcount = bfd_canonicalize_reloc(ibfd, isec, relpp, sympp);
bfd_set_reloc(obfd, osec, relpp, relcount);

But I can not use bfd_canonicalize_reloc() to get info from out format 
and I have to fill each reloc entry manually. Is this the right way or 
should I use something like this:

arelent_chain *reloc = (arelent_chain *)bfd_alloc(abfd, 
sizeof(arelent_chain));
...
rel_section->constructor_chain = reloc;

Problem is, there is not function bfd_alloc() in my bfd.h and I did not 
find it in latest binutils either. What happend to it ?

Thanks for advices.
Peter Matula

Re: create relocation entry from scratch

[Ian Lance Taylor]

peter matula <xmatul01@stud.fit.vutbr.cz> writes:

> I'm using BFD to transform our internal binary format to ELF. I have
> already successfully made transformation of executable files which can
> be described like this:
>
> CreateBfd();    // create BFD file
> GetArch();    // convert arch and mach info from our format to BFD
> CreateSections();    // create sections in BFD
> GetSymtab();    // create and fill symbol table
> GetSectionData();    // copy data from out format to BFD
> CloeBfd();    // write and close BFD
>
> Now i would like to add relocation conversion.

In the general case, this is impossible.  However, it can be done if all
of the relocations in your internal format can be represented in ELF.

> And how should i create relocation entry from scratch ? I found few
> examples like this:
>
> relpp = (arelent **) xmalloc(get_reloc_upper_bound(ibfd, isec));
> relcount = bfd_canonicalize_reloc(ibfd, isec, relpp, sympp);
> bfd_set_reloc(obfd, osec, relpp, relcount);
>
> But I can not use bfd_canonicalize_reloc() to get info from out format
> and I have to fill each reloc entry manually.

This is the right way.  Yes, you have to fill in each entry manually.

> Is this the right way or
> should I use something like this:
>
> arelent_chain *reloc = (arelent_chain *)bfd_alloc(abfd,
> sizeof(arelent_chain));
> ...
> rel_section->constructor_chain = reloc;

That is really just another way of doing the first one.  Don't use it.

> Problem is, there is not function bfd_alloc() in my bfd.h and I did
> not find it in latest binutils either. What happend to it ?

bfd_alloc is an internal function declared in libbfd.h.  You don't need
to use it.

Ian

Re: create relocation entry from scratch

[peter matula]

On 15.07.2010 15:28, Ian Lance Taylor wrote:
>> relpp = (arelent **) xmalloc(get_reloc_upper_bound(ibfd, isec));
>> relcount = bfd_canonicalize_reloc(ibfd, isec, relpp, sympp);
>> bfd_set_reloc(obfd, osec, relpp, relcount);
>>
>> But I can not use bfd_canonicalize_reloc() to get info from out format
>> and I have to fill each reloc entry manually.
>
> This is the right way.  Yes, you have to fill in each entry manually.
>
> Ian

Alright, thanks. But when should I create relocations ? During section 
creating or later when there will be symbol table ?

Peter Matula