New gABI/ELF Spec Available for Public Review

[Cary Coutant]

A draft of Version 4.3 of the ELF specification is now available for
public review, in both HTML and PDF:

https:://gabi.xinuos.com

The ELF specification was formerly part (chapters 4 and 5) of the SVR4
gABI document, but I have separated it from the gABI document to
better serve as a specification independent of the SVR4 ABI.

The last published gABI documents were the Fourth Edition and a draft
of Edition 4.1, both published in March 1997. The ELF portions of the
document were updated several times between 1998 and 2015, published
online as drafts at:

https://www.sco.com/developers/devspecs/

I've published the last draft from 2015 as Version 4.2, and collected
the several changes since then, along with new e_machine values, as
Version 4.3.

Version 4.2 (based on the fifteenth draft after Edition 4.1, from July 23, 2015)

- Converted to ReStructuredText.
- ELF specification is now separate from the gABI document.
- Removed empty placeholders for psABI sections.

Version 4.3 (DRAFT)

- Added extra requirements for SHF_LINKORDER flag.
- Added relative relocation table (Elf32_Relr and Elf64_Relr).
- Changed the symbol visibility attribute to use the lower 3 bits of
st_other (instead of 2 bits).
- Added DT_SYMTABSZ entry, and made DT_HASH optional if DT_SYMTABSZ is provided.
- Changed SHF_COMPRESSED to allow with SHF_ALLOC sections in ET_REL objects.
- Added ELFCOMPRESS_ZSTD compression algorithm.

Version 4.2, for reference, is available at:

https://gabi.xinuos.com/v42/

The source is on github:

https://github.com/xinuos/gabi

I've collected the gABI mailing list discussions for the changes
listed above for Version 4.3 as the first six issues in the issue
tracker.

-cary

[H.J. Lu]

Thanks. I really appreciate it.

> -cary
>


--
H.J.

[Fangrui Song]

On Tuesday, September 2, 2025 at 7:48:56 PM UTC-7 H.J. Lu wrote:

Thank you for creating the new website and maintaining the specification!
The August 2015 post marked the start of the unmaintenained period https://groups.google.com/g/generic-abi/c/IakWYdGABjQ
After a decade, we now have an official live specification once again!

Updated my notes as well https://maskray.me/blog/2024-05-26-evolution-of-elf-object-file-format 

[Michael Matz]

Heyho,

On Tue, 2 Sep 2025, Cary Coutant wrote:

> A draft of Version 4.3 of the ELF specification is now available for
> public review, in both HTML and PDF:
>
> https:://gabi.xinuos.com

...
> - Converted to ReStructuredText.
...

> The source is on github:
>
> https://github.com/xinuos/gabi

Hurray! Thank you for persisting through it, Cary! I'm very happy.


Cioa,
Michael.

[Mark Wielaard]

Hi Cary,

On Tue, 2025-09-02 at 19:30 -0700, Cary Coutant wrote:
> I've published the last draft from 2015 as Version 4.2, and collected
> the several changes since then, along with new e_machine values, as
> Version 4.3.
>
> Version 4.2 (based on the fifteenth draft after Edition 4.1, from July 23, 2015)
>
> - Converted to ReStructuredText.
> - ELF specification is now separate from the gABI document.
> - Removed empty placeholders for psABI sections.
>
> Version 4.3 (DRAFT)
>
> - Added extra requirements for SHF_LINKORDER flag.
> - Added relative relocation table (Elf32_Relr and Elf64_Relr).
> - Changed the symbol visibility attribute to use the lower 3 bits of
> st_other (instead of 2 bits).
> - Added DT_SYMTABSZ entry, and made DT_HASH optional if DT_SYMTABSZ is provided.
> - Changed SHF_COMPRESSED to allow with SHF_ALLOC sections in ET_REL objects.
> - Added ELFCOMPRESS_ZSTD compression algorithm.
>
> Version 4.2, for reference, is available at:
>
> https://gabi.xinuos.com/v42/
>
> The source is on github:
>
> https://github.com/xinuos/gabi

Very nice! Thanks so much.

Could you add a license to it so it is clear what the redistribution
terms are and under which terms the supplement psABI documents may
reuse the text?

Thanks,

Mark

[Cary Coutant]

> Could you add a license to it so it is clear what the redistribution
> terms are and under which terms the supplement psABI documents may
> reuse the text?

Working on it. I've proposed a more permissive license to the Xinuos
legal team, and need their approval.

-cary

[Cary Coutant]

By the way, I'd like to thank Ali Bahrami and Carlos O'Donell for
their thorough and constructive reviews of earlier drafts of this
work.

-cary

[ali_e...@emvision.com]

On 9/2/25 8:30 PM, Cary Coutant wrote:
> Version 4.2, for reference, is available at:
>
> https://gabi.xinuos.com/v42/
>
> The source is on github:
>
> https://github.com/xinuos/gabi

Even though I saw an earlier draft, and had a pretty
good idea of what to expect, I'm really impressed by how good
this is. It's quite a leap from the previous edition.

You've done a huge service for the rest of us, and one that I
doubt could have happened otherwise. We're set for years to
come now.

Thank You!

- Ali