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[AAELF64][PAUTHABI64] Assign PAuthABI relocation codes. #227

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Mar 18, 2024
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[AAELF64][PAUTHABI64] Assign PAuthABI relocation codes. #227

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85 changes: 55 additions & 30 deletions aaelf64/aaelf64.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -277,6 +277,9 @@ changes to the content of the document for that release.
| | | `Dynamic Linking`. Move description to|
| | | `SYSVABI64`_ |
+---------------+--------------------+-----------------------------------------+
| 2024Q1 | 18\ :sup: `th` | - Move relocation codes from |
| | March 2024 | `PAUTHABIELF64`_ into reserved space |
+---------------+--------------------+-----------------------------------------+

References
----------
Expand Down Expand Up @@ -1675,6 +1678,22 @@ Thread-local storage descriptors
Relocation codes ``R_<CLS>_TLSDESC_LDR``, ``R_<CLS>_TLSDESC_ADD`` and ``R_<CLS>_TLSDESC_CALL`` are needed to permit linker optimization of TLS descriptor code sequences to use Initial-exec or Local-exec TLS sequences; this can only be done if all relevant uses of TLS descriptors are marked to permit accurate relaxation. Object producers that are unable to satisfy this requirement must generate traditional General-dynamic TLS
sequences using the relocations described in `General Dynamic thread-local storage model`_. The details of TLS descriptors are beyond the scope of this specification; a general introduction can be found in [TLSDESC_].

Relocations for PAuth ABI Extension
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

The PAuth ABI Extension defines a number of static and dynamic relocations.
The information in this document is sufficient to reserve the relocation types.
For details on the relocations and operations see `PAUTHABIELF64`_.

.. class:: aaelf64-pauth-descriptor-relocations

.. table:: PAuthABI static relocations

+------------+------------+---------------------------------+----------------------------------+-----------------------------------------------------+
| ELF64 Code | ELF32 Code | Name | Operation | Comment |
+============+============+=================================+==================================+=====================================================+
| 580 | \- | R\_<CLS\_AUTH\_ABS64 | PAUTH(S+A) | See `PAUTHABIELF64`_ |
+------------+------------+---------------------------------+----------------------------------+-----------------------------------------------------+

Dynamic relocations
^^^^^^^^^^^^^^^^^^^
Expand All @@ -1685,36 +1704,41 @@ The dynamic relocations for those execution environments that support only a lim

.. table:: Dynamic relocations

+------------+------------+-------------------------+------------------------+-------------------------------------------+
| ELF64 Code | ELF32 Code | Name | Operation | Comment |
+============+============+=========================+========================+===========================================+
| 257 | \- | R\_<CLS>\_ABS64 | S + A | See note below. |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| \- | 1 | R\_<CLS>\_ABS32 | S + A | See note below. |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| 1024 | 180 | R\_<CLS>\_COPY | | See note below. |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| 1025 | 181 | R\_<CLS>\_GLOB\_DAT | S + A | See note below |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| 1026 | 182 | R\_<CLS>\_JUMP\_SLOT | S + A | See note below |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| 1027 | 183 | R\_<CLS>\_RELATIVE | Delta(S) + A | See note below |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| 1028 | 184 | R\_<CLS>\_TLS\_IMPDEF1 | | See note below |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| 1029 | 185 | R\_<CLS>\_TLS\_IMPDEF2 | | See note below |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| | | R\_<CLS>\_TLS\_DTPREL | DTPREL(S+A) | See note below |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| | | R\_<CLS>\_TLS\_DTPMOD | LDM(S) | See note below |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| 1030 | 186 | R\_<CLS>\_TLS\_TPREL | TPREL(S+A) | |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| 1031 | 187 | R\_<CLS>\_TLSDESC | TLSDESC(S+A) | Identifies a TLS descriptor to be filled |
+------------+------------+-------------------------+------------------------+-------------------------------------------+
| 1032 | 188 | R\_<CLS>\_IRELATIVE | Indirect(Delta(S) + A) | See note below. |
+------------+------------+-------------------------+------------------------+-------------------------------------------+

+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| ELF64 Code | ELF32 Code | Name | Operation | Comment |
+============+============+==========================+=================================+===========================================+
| 257 | \- | R\_<CLS>\_ABS64 | S + A | See note below. |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| \- | 1 | R\_<CLS>\_ABS32 | S + A | See note below. |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 580 | \- | R\_<CLS\_AUTH\_ABS64 | PAUTH(S + A) | See note below. |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1024 | 180 | R\_<CLS>\_COPY | | See note below. |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1025 | 181 | R\_<CLS>\_GLOB\_DAT | S + A | See note below |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1026 | 182 | R\_<CLS>\_JUMP\_SLOT | S + A | See note below |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1027 | 183 | R\_<CLS>\_RELATIVE | Delta(S) + A | See note below |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1028 | 184 | R\_<CLS>\_TLS\_IMPDEF1 | | See note below |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1029 | 185 | R\_<CLS>\_TLS\_IMPDEF2 | | See note below |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| | | R\_<CLS>\_TLS\_DTPREL | DTPREL(S+A) | See note below |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| | | R\_<CLS>\_TLS\_DTPMOD | LDM(S) | See note below |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1030 | 186 | R\_<CLS>\_TLS\_TPREL | TPREL(S+A) | |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1031 | 187 | R\_<CLS>\_TLSDESC | TLSDESC(S+A) | Identifies a TLS descriptor to be filled |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1032 | 188 | R\_<CLS>\_IRELATIVE | Indirect(Delta(S) + A) | See note below. |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1040 | \- | R\_<CLS>\_AUTH\_ABS64 | SIGN(S + A, SCHEMA(\*P)) | See note below. |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+
| 1041 | \- | R\_<CLS>\_AUTH\_RELATIVE | SIGN(DELTA(S) + A, SCHEMA(\*P)) | See note below. |
+------------+------------+--------------------------+---------------------------------+-------------------------------------------+

With the exception of ``R_<CLS>_COPY`` all dynamic relocations require that the place being relocated is an 8-byte aligned 64-bit data location in ELF64 or a 4-byte aligned 32-bit data location in ELF32.

Expand Down Expand Up @@ -1746,6 +1770,7 @@ Relocations ``R_AARCH64_TLS_DTPREL``, ``R_AARCH64_TLS_DTPMOD`` and ``R_AARCH64_T

It is implementation defined whether ``R_<CLS>_TLS_IMPDEF1`` implements ``R_<CLS>_TLS_DTPREL`` and ``R_<CLS>_TLS_IMPDEF2`` implements ``R_<CLS>_TLS_DTPMOD`` or whether ``R_<CLS>_TLS_IMPDEF1`` implements ``R_<CLS>_TLS_DTPMOD`` and ``R_<CLS>_TLS_IMPDEF2`` implements ``R_<CLS>_TLS_DTPREL``; a platform must document its choice\ [#aaelf64-f1]_.

``R\_<CLS\_AUTH\_ABS64``, ``R\_<CLS>\_AUTH\_ABS64`` and ``R\_<CLS>\_AUTH\_RELATIVE`` are part of the PAuth ABI Extension. For details on the relocations and operations see `PAUTHABIELF64`_.

Private and platform-specific relocations
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Expand Down
7 changes: 4 additions & 3 deletions pauthabielf64/pauthabielf64.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -236,6 +236,7 @@ changes to the content of the document for that release.
| | | DT_AARCH64_VARIANT_PCS. |
+------------+-----------------------------+------------------------------------------------------------------+
| 2024Q1 | 29\ :sup:`th` January 2024 | Update preferred ELF marking scheme to be GNU property based |
| 2023Q4 | 18\ :sup:`th` March 2024 | Update relocation codes to move out of private experiments space.|
+------------+-----------------------------+------------------------------------------------------------------+

References
Expand Down Expand Up @@ -704,7 +705,7 @@ Static Data relocations
| | | | |
| | | | |
+=============+==========================+================+=====================================================+
| 0xE100 | R\_AARCH64\_AUTH\_ABS64 | ``PAUTH(S+A)`` | Signing schema encoded in the contents of the place |
| 0x244 | R\_AARCH64\_AUTH\_ABS64 | ``PAUTH(S+A)`` | Signing schema encoded in the contents of the place |
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@asl asl Nov 8, 2023 •
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We are having two relocations named R_AARCH64_AUTH_ABS64 with different ids (static and dynamic). Should this be named R_AARCH64_AUTH_ABS64_STATIC as otherwise there is an ambiguity?

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This is the same as R_AARCH64_ABS64 which can be both a static and dynamic relocation. I followed that convention as R_AARCH64_AUTH_ABS64 is its PAuth equivalent.

Changing codes is possible but I thought it better to stick the existing convention.

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It's not the code, it's the name. Essentially we cannot put these two relocations into a single enum – we'd need to rename one entry.

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Actually I think it is the code, and I've made a mistake, sorry.

The intention is that the name and code remain the same. In the original both had 0xE100, but in the new one I used the first code in the dynamic range, it needed to retain its original 0x244. I'll update the pull request.

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I've updated the value. I had it right in aaelf64.rst but not here.

+-------------+--------------------------+----------------+-----------------------------------------------------+

In the static context, this is the equivalent of the arm64e
Expand All @@ -731,9 +732,9 @@ relocation.
+--------------------+------------------------------+------------------------------------+
| Relocation code | Name | Operation |
+====================+==============================+====================================+
| 0xE100 | R\_AARCH64\_AUTH\_ABS64 | SIGN(S + A, SCHEMA(\*P)) |
| 0x244 | R\_AARCH64\_AUTH\_ABS64 | SIGN(S + A, SCHEMA(\*P)) |
+--------------------+------------------------------+------------------------------------+
| 0xE200 | R\_AARCH64\_AUTH\_RELATIVE | SIGN(DELTA(S) + A, SCHEMA(\*P)) |
| 0x411 | R\_AARCH64\_AUTH\_RELATIVE | SIGN(DELTA(S) + A, SCHEMA(\*P)) |
+--------------------+------------------------------+------------------------------------+

.. raw:: pdf
Expand Down
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