Embedding stuff in ELF section of compiled module

Embedding stuff in ELF section of compiled module

[Olivier Dion]

Hi,

TLDR; Is there a way to embed a bytevector into a ELF section of a
compiled module (.go)?

I have a case where I want to generate bytevectors that follow an ABI
for event description of static tracepoints.  I would like this
bytevector to be put into a know ELF section of the compiled module so
that external tools can reference it by parsing the ELF file,
i.e. without running Guile.  I personnaly don't care about none-ELF
systems, so I'm fine if this solution is Linux only.

I guess this is similar to embedding something else like an audio/image
for a video game.

So, is there any way for adding section to the compiled ELF, something
along like:

 (embed-bytevector ".my_section"
         #vu8(bytes ...))

If not, I wonder if this is something that could be appreciated for
other users as well?

Thanks,
Olivier

-- 
Olivier Dion
EfficiOS Inc.
https://www.efficios.com

Re: Embedding stuff in ELF section of compiled module

[Matt Wette]

On 11/9/24 7:15 AM, Olivier Dion wrote:
> Hi,
>
> TLDR; Is there a way to embed a bytevector into a ELF section of a
> compiled module (.go)?
>
> I have a case where I want to generate bytevectors that follow an ABI
> for event description of static tracepoints.  I would like this
> bytevector to be put into a know ELF section of the compiled module so
> that external tools can reference it by parsing the ELF file,
> i.e. without running Guile.  I personnaly don't care about none-ELF
> systems, so I'm fine if this solution is Linux only.
>
> I guess this is similar to embedding something else like an audio/image
> for a video game.
>
> So, is there any way for adding section to the compiled ELF, something
> along like:
>
>   (embed-bytevector ".my_section"
>           #vu8(bytes ...))
>
> If not, I wonder if this is something that could be appreciated for
> other users as well?
>
> Thanks,
> Olivier
>

You could look at `objcopy' to add a section to the .go file (outside of 
Guile).

Otherwise, dig into the code in share/guile/3.0/system/vm/elf.scm.

Matt

RE: Embedding stuff in ELF section of compiled module

[Maxime Devos via General Guile related discussions]

>TLDR; Is there a way to embed a bytevector into a ELF section of a
compiled module (.go)?

Yes, all (referenced) bytevectors end up somewhere. But going by the rest, it needs to be in some section in particular.

>So, is there any way for adding section to the compiled ELF, something
along like:
> (embed-bytevector ".my_section"
         #vu8(bytes ...))

Except perhaps for external tools (like 'objcopy’ mentioned elsewhere), not yet. At least, I think I would remember reading about such a mechanism.

So, answer is yes: the way to do this is too add support to Guile for this.

That said, are you sure it’s a separate section you want? Perhaps an entry in the (ELF) symbol table would do as well (and these are already populated, though I don’t recall to what extent).

Best regards,
Maxime Devos