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[AAELF64] Make R_<CLS>_PREL32 and 16 signed. #401

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smithp35 merged 1 commit into from
Jun 30, 2026
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[AAELF64] Make R_<CLS>_PREL32 and 16 signed. #401

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9 changes: 6 additions & 3 deletions aaelf64/aaelf64.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -300,6 +300,9 @@ changes to the content of the document for that release.
| | | - R_AARCH64_TLS_DTPREL can be used as a |
| | | static relocation as well as dynamic |
+---------------+--------------------+-----------------------------------------+
| 2026Q2 | 29\ :sup:`th` | - In `Call and Jump relocations`_ make |
| | | pc-relative relocaions signed. |
+---------------+--------------------+-----------------------------------------+

References
----------
Expand Down Expand Up @@ -1125,17 +1128,17 @@ See also table `GOT-relative data relocations`_.
| | | | | No overflow check. |
+---------+---------+----------------------+-----------+------------------------------------------------------------------+
| 261 | 3 | R\_<CLS>\_PREL32 | S + A - P | Write bits [31:0] of X at byte-aligned place P. |
| | | | | Check that -2\ :sup:`31` <= X < 2\ :sup:`32`. |
| | | | | Check that -2\ :sup:`31` <= X < 2\ :sup:`31`. |
+---------+---------+----------------------+-----------+------------------------------------------------------------------+
| 262 | 4 | R\_<CLS>\_PREL16 | S + A - P | Write bits [15:0] of X at byte-aligned place P. |
| | | | | Check that -2\ :sup:`15` <= X < 2\ :sup:`16`. |
| | | | | Check that -2\ :sup:`15` <= X < 2\ :sup:`15`. |
+---------+---------+----------------------+-----------+------------------------------------------------------------------+
| 314 | 29 | R\_<CLS>\_PLT32 | S + A - P | Write bits [31:0] of X at byte-aligned place P. |
| | | | | Check that -2\ :sup:`31` <= X < 2\ :sup:`31`. |
| | | | | See `Call and Jump relocations`_. |
+---------+---------+----------------------+-----------+------------------------------------------------------------------+

With the exception of ``R_<CLS>_PLT32``, these overflow ranges permit either signed or unsigned narrow values to be created from the intermediate result viewed as a 64-bit signed integer. If the place is intended to hold a narrow signed value and ``INTn_MAX < X <= UINTn_MAX``, no overflow will be detected but the positive result will be interpreted as a negative value.
For the relocations with a S + A operation, these overflow ranges permit either signed or unsigned narrow values to be created from the intermediate result viewed as a 64-bit signed integer. If the place is intended to hold a narrow signed value and ``INTn_MAX < X <= UINTn_MAX``, no overflow will be detected but the positive result will be interpreted as a negative value.

@jrtc27 jrtc27 Jul 1, 2026

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This feels a bit indirect of a way to just say "For the R_<CLS>_ABSn relocations"? Also, arguably the other relocations do have an S + A operation nested inside an S + A - P one.

@smithp35 smithp35 Jul 2, 2026

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My first draft said absolute relocations, then I'd need to define which ones were absolute and settled for S+A as that was the entry in the table.

Can try and reword using the relocation names and a prefix in a separate patch, likely next week though.

@Wilco1 Wilco1 Jul 2, 2026

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In principle this whole paragraph could be removed once we agree that ABS relocations are always unsigned (#402).



Static AArch64 relocations
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