Skip to content

[sysvabi64] Code Models. Limit range to GOT to 2GiB #345

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
smithp35 merged 2 commits into from
Aug 21, 2025
Merged

[sysvabi64] Code Models. Limit range to GOT to 2GiB #345

Changes from 1 commit
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
6217919
[sysvabi64] Code Models. Limit range to GOT to 2GiB
smithp35 Aug 15, 2025
92dc432
[sysvabi64] Remove GOT distance from table
smithp35 Aug 15, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
22 changes: 16 additions & 6 deletions sysvabi64/sysvabi64.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -216,6 +216,7 @@ Change History
| 2025Q2 | 20\ :sup:`th` June 2024 | Require that ``PT_GNU_PROPERTY`` program header be |
| | | present in executables and shared-libraries if a |
| | | .note.gnu.property section is present. |
| | | - Update distance to GOT for small code-model |
+------------+------------------------------+-------------------------------------------------------+

References
Expand Down Expand Up @@ -708,11 +709,17 @@ along with the assumptions that the code model may make.
| tiny | 1 MiB | 1 Mib | none |
| | | | |
+--------+----------------+----------------+------------------------+
| small | 2GiB | 4 GiB | pic: got size < 32 KiB |
| small | 2GiB | 4 GiB | max distance from text |
| | | | to GOT < 2 GiB |
| | | +------------------------+
| | | | pic: got size < 32 KiB |
| | | +------------------------+
| | | | PIC: none |
+--------+----------------+----------------+------------------------+
| medium | 2GiB | no restriction | pic: got size < 32 KiB |
| medium | 2GiB | no restriction | max distance from text |
| | | | to GOT < 2 GiB |
| | | +------------------------+
| | | | pic: got size < 32 KiB |
| | | +------------------------+
| | | | PIC: none |
+--------+----------------+----------------+------------------------+
Expand Down Expand Up @@ -750,23 +757,26 @@ along with the assumptions that the code model may make.
5. The text segment maximum size is limited to 2GiB by
R_AARCH64_PLT32 relocations from ``.eh_frame`` sections.

6. While designing the code models it was estimated that only 2.6%
6. The distance to the GOT in the small and medium code model is
limited to 2GiB by the R_AARCH64_GOTPCREL32 relocations.
Copy link
Contributor

@Wilco1 Wilco1 Aug 15, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Basically in all cases (including large model) the max distance from text to GOT is 2GB if R_AARCH64_GOTPCREL32 is used. It is 4GB otherwise as the basic range of ADRP.

So I think it doesn't really need to be added to the table since there is no difference between the code models.

Copy link
Contributor Author

@smithp35 smithp35 Aug 15, 2025

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Main reason I did that was the large code model (need to expand the text of the diff to see) says

| large  | 2GiB           | no restriction | max distance from text |
|        |                |                | to GOT < 4 GiB         |

If I take the table entries out, I'll need to take that out too. Will update the PR.


7. While designing the code models it was estimated that only 2.6%
of load modules (executables and dynamic shared objects) have a max
text segment size greater than 1MiB; the rest would all fit into the
tiny model. However to avoid build option changes, it is recommended
that the small model should be the default, with an explicit option
to select the tiny model.

7. Executables and shared objects may be linked dynamically with other
8. Executables and shared objects may be linked dynamically with other
shared objects which use a different code model.

8. Linking of relocatable objects of different code models is possible
9. Linking of relocatable objects of different code models is possible
as is linking of PIC/PIE and non-PIC relocatable objects. The result
of the combination is always the most limited model. For example the
combination of a tiny code model PIC object and small code model
non-PIC object is a tiny non-PIC executable.

9. The large code model is aimed at programs with large amounts of
10. The large code model is aimed at programs with large amounts of
read-write data, not large amounts or sparsely placed code.

Implementation of code models
Expand Down