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[aadwarf64] Add DWARF support for unwinding with FEAT_PAuth_LR enabled #245

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Mar 7, 2024
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[aadwarf64] Add DWARF support for unwinding with FEAT_PAuth_LR enabled #245

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[aadwarf64] Add DWARF support for unwinding with FEAT_PAuth_LR enabled
pratlucas Feb 8, 2024
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fixup! [aadwarf64] Add DWARF support for unwinding with FEAT_PAuth_LR…
pratlucas Feb 26, 2024
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64 changes: 48 additions & 16 deletions aadwarf64/aadwarf64.rst
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Expand Up @@ -470,11 +470,31 @@ integers.
.. _Note 8:

8. The RA_SIGN_STATE pseudo-register records whether the return address has
been signed with a PAC. This information can be used when unwinding. It
is an unsigned integer with the same size as a general register. Only
bit[0] is meaningful and is initialized to zero. A value of 0 indicates
the return address has not been signed. A value of 1 indicates the return
address has been signed.
been signed with a PAC, and whether the value of PC has been used as a
diversifier for the return address signing. This information can be used
when unwinding. It is an unsigned integer with the same size as a general
register. Only bit[0] and bit[1] are meaningful and are initialized to zero.
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Bit[0] indicates whether the return address has been signed. A value of 0
indicates the return address has not been signed. A value of 1 indicates
the return address has been signed.

Bit[1] indicates whether the value of PC has been used as a diversifier for
signing the return address. A value of 0 indicates the value of PC has not
been used for return address signing. A value of 1 indicates the value of PC
has been used for return address signing.

+--------+--------+----------------------------------+
| Bit[1] | Bit[0] | State |
+========+========+==================================+
| 0 | 0 | Return address not signed |
+--------+--------+----------------------------------+
| 0 | 1 | Return address signed with SP |
+--------+--------+----------------------------------+
| 1 | 1 | Return address signed with SP+PC |
+--------+--------+----------------------------------+
| 1 | 0 | Invalid state |
+--------+--------+----------------------------------+

.. _Note 9:

Expand Down Expand Up @@ -574,25 +594,37 @@ a CIE augmentation string.
Call frame instructions
-----------------------

This ABI defines one vendor call frame instruction
``DW_CFA_AARCH64_negate_ra_state``.
This ABI defines the following vendor call frame instructions:
``DW_CFA_AARCH64_negate_ra_state`` and ``DW_CFA_AARCH64_negate_ra_state_with_pc``.

.. class:: aadwarf64-vendor-cfa-operations

.. table:: AArch64 vendor CFA operations

+------------------------------------+-------------+------------+-----------+-----------+
| Instruction | High 2 bits | Low 6 bits | Operand 1 | Operand 2 |
+====================================+=============+============+===========+===========+
| ``DW_CFA_AARCH64_negate_ra_state`` | 0 | ``0x2D`` | \- | \- |
+------------------------------------+-------------+------------+-----------+-----------+
+--------------------------------------------+-------------+------------+-----------+-----------+
| Instruction | High 2 bits | Low 6 bits | Operand 1 | Operand 2 |
+============================================+=============+============+===========+===========+
| ``DW_CFA_AARCH64_negate_ra_state`` | 0 | ``0x2D`` | \- | \- |
+--------------------------------------------+-------------+------------+-----------+-----------+
| ``DW_CFA_AARCH64_negate_ra_state_with_pc`` | 0 | ``0x2C`` | \- | \- |
+--------------------------------------------+-------------+------------+-----------+-----------+

The ``DW_CFA_AARCH64_negate_ra_state`` operation negates bit[0] of the
RA_SIGN_STATE pseudo-register. It does not take any operands.
The ``DW_CFA_AARCH64_negate_ra_state`` must not be mixed with other DWARF
Register Rule Instructions (GDWARF_, §6.4.2.3) on the RA_SIGN_STATE
pseudo-register in one Common Information Entry (CIE) and Frame Descriptor
Entry (FDE) program sequence.

The ``DW_CFA_AARCH64_negate_ra_state_with_pc`` operation negates bit[0] and
bit[1] of the RA_SIGN_STATE pseudo-register, and instructs the unwinder to
capture the current code location. The code location information can be used
for authenticating the return address.

The ``DW_CFA_AARCH64_negate_ra_state_with_pc`` instruction must be placed within
the debug frame in a position that refers to the exact code location of the
signing/authenticating PAC instructions.

The ``DW_CFA_AARCH64_negate_ra_state`` and ``DW_CFA_AARCH64_negate_ra_state_with_pc``
instructions must not be mixed with other DWARF Register Rule Instructions
(GDWARF_, §6.4.2.3) on the RA_SIGN_STATE pseudo-register in one Common
Information Entry (CIE) and Frame Descriptor Entry (FDE) program sequence.

.. _DWARF expression operations:

Expand Down
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