[aadwarf64]] Add DW_CFA_AARCH64_set_ra_state stack frame operation #346

walkerkd · 2025-08-21T13:31:35Z

The DW_CFA_AARCH64_set_ra_state operation updates the RA_SIGN_STATE pseudo register with the current signing state. If the signing state includes signing is DW_AARCH64_RA_SIGNED_SP_PC, then it also provides the offset to the signing instruction so that the PC value used in the signing can be calculated.

The DW_CFA_AARCH64_negate_ra_state_with_pc operation has been marked as deprecated. This is because it has been found that it is not suitable for describing all cases where the PC was used to sign the return address (see #327)

The contents of the RA_SIGN_STATE pseudo register is also changed from being described in terms of a set of bits to being a series of defined values.

Previously the state of the RA_SIGN_STATE pseudo register was changed implicitly by the DW_CFA_AARCH64_negate_ra_state and DW_CFA_AARCH64_set_ra_state operations. This meant that the actual encoding was actually internal to any implementation.

Now with the introduction of the DW_CFA_AARCH64_set_ra_state operation the encoding has been made externally visible. So the opportunity has been taken now to change the encoding to a simpler form.

The DW_CFA_AARCH64_set_ra_state operation updates the RA_SIGN_STATE pseudo register with the current signing state. If the signing state includes signing is DW_AARCH64_RA_SIGNED_SP_PC, then it also provides the offset to the signing instruction so that the PC value used in the signing can be calculated. The DW_CFA_AARCH64_negate_ra_state_with_pc operation has been marked as deprecated. This is because it has been found that it is not suitable for describing all cases where the PC was used to sign the return address (see ARM-software#327) The contents of the RA_SIGN_STATE pseudo register is also changed from being described in terms of a set of bits to being a series of defined values. Previously the state of the RA_SIGN_STATE pseudo register was changed implicitly by the DW_CFA_AARCH64_negate_ra_state and DW_CFA_AARCH64_set_ra_state operations. This meant that the actual encoding was actually internal to any implementation. Now with the introduction of the DW_CFA_AARCH64_set_ra_state operation the encoding has been made externally visible. So the opportunity has been taken now to change the encoding to a simpler form.

bgergely0 · 2025-08-26T08:48:44Z

aadwarf64/aadwarf64.rst

+  |        |                             | - Deprecated                           |
+  |        |                             |   DW_CFA_AARCH64_negate_ra_state.      |


I believe this should be DW_CFA_AARCH64_negate_ra_state_with_pc.

Thanks for spotting that. I'll fix it.

Incorrect change history deprecated state DW_CFA_AARCH64_negate_ra_state corrected to DW_CFA_AARCH64_negate_ra_state_with_pc

rearnsha

A couple of grammatical nits/comments and I think we should add some background to the deprecation of ...negate_ra_state_with_pc

rearnsha · 2026-01-07T14:07:46Z

aadwarf64/aadwarf64.rst


   9. Normally, the program counter is restored from the return address, however
-      having both LR and PC columns is useful for describing asynchronously
+      having both LR and PC diversifiers are useful for describing asynchronously


I think in this context, 'having both ... is useful' is the correct form. 'having both' here creates a singular subject for the sentence.

rearnsha · 2026-01-07T14:07:53Z

aadwarf64/aadwarf64.rst

+The ``DW_CFA_AARCH64_set_ra_state`` instruction takes two operands; an unsigned
+LEB128 value representing a return address state ra_state and a signed LEB128
+factored offset. The required action is to set the RA_SIGN_STATE pseudo-register


I would use '...takes two operands: an unsigned ...; and a signed ...' to

Done. The current style is what is used in the base DWARF specification. But the suggested change does make it clearer what are the 2 operands.

rearnsha · 2026-01-07T14:09:51Z

aadwarf64/aadwarf64.rst

+as the signing/authenticating PAC instruction, otherwise it is has the value 0.
+The code location information can be used for authenticating the return address.
+
+The ``DW_CFA_AARCH64_negate_ra_state_with_pc`` operation toggles between the


Shouldn't this re-emphasize that this is deprecated (and perhaps explain why)?

I have added a statement to re-emphasize that this instruction is deprecate and a short explanation in non-normative text (the base DWARF specification does this by using italics for non-normative text so I have used the same convention here).

- Fixes some minor grammatical issues. - Add an explicit deprecation statement for the DW_CFA_AARCH64_negate_ra_state_with_pc instruction in the section describing the instruction. It has already been marked as deprecated in the AArch64 vendor CFA operations table.

Stylie777

From a Compiler Development POV this change makes sense, and addresses the issue of the CFI collecting an incorrect PC value.

Have you got an example that demonstrates the change in Assembly that will be generated? Would be helpful for me so I can visualise the changes being made.

walkerkd · 2026-01-14T15:33:07Z

So the example from the original defect pseudo-assembler report #327 where I have also added the PACPC / AUTPC instructions:

  .cfi_startproc 
func:
   // Frame setup
   .cfi_save ...
   PACPC
   .cfi_negate_ra_with_pc  // Save auth state and remember location
   some code
   CBZ L0
   some more code
   // Restore frame
   AUTPC SIGNED 
   .cfi_negate_ra_with_pc  // Restore state (using previously stored location)
   .cfi_restore ...
   RET
L0:
   .cfi_save ...
   .cfi_negate_ra_with_pc  // ERROR - this saves the wrong location
   Some additional code
   AUTPC SIGNED 
   .cfi_negate_ra_with_pc     // Uses wrong location.
   RET
...

This updated form using the new DW_CFA_AARCH64_set_ra_state instruction would be:

  .cfi_startproc 
func:
   // Frame setup
   .cfi_save ...
SIGNED:
   PACPC
   cfi_set_ra_state DW_AARCH64_RA_SIGNED_SP, factored_offset_SIGNED  // Auth state LR & PC (signed with SIGNED)
   some code
   CBZ L0
   some more code
   // Restore frame
   AUTPC SIGNED 
   .cfi_set_ra_state DW_AARCH64_RA_NOT_SIGNED, factored_offset_SIGNED  // Auth state unsigned
   .cfi_restore ...
   RET
L0:
   .cfi_save ...
   .cfi_set_ra_state DW_AARCH64_RA_SIGNED_SP, factored_offset_SIGNED  // Auth state LR & PC (signed with SIGNED)
   Some additional code
   AUTPC SIGNED 
   .cfi_set_ra_state DW_AARCH64_RA_NOT_SIGNED, factored_offset_SIGNED  // Auth state unsigned
   RET
...

where factored_offset_SIGNED is (SIGNED-currentPC)/code_alignment_factor.
code_alignment_factor is defined in the CFI header.

Hopefully this makes it clearer what the change means to an implementation using the new instruction.

Stylie777

Thanks @walkerkd, this looks good and makes sense from my POV

bgergely0 reviewed Aug 26, 2025

View reviewed changes

walkerkd and others added 3 commits September 23, 2025 09:57

Merge branch 'ARM-software:main' into master

2f36d5e

Merge branch 'ARM-software:main' into master

8685f8d

[AADWARF64] Update change history with correction

75d728f

Incorrect change history deprecated state DW_CFA_AARCH64_negate_ra_state corrected to DW_CFA_AARCH64_negate_ra_state_with_pc

rearnsha suggested changes Jan 7, 2026

View reviewed changes

walkerkd and others added 2 commits January 7, 2026 15:03

Merge branch 'ARM-software:main' into master

4ca030b

Stylie777 reviewed Jan 14, 2026

View reviewed changes

Stylie777 approved these changes Jan 16, 2026

View reviewed changes

stuij merged commit 1d6cf2e into ARM-software:main Jan 19, 2026
1 check passed

[aadwarf64]] Add DW_CFA_AARCH64_set_ra_state stack frame operation #346

[aadwarf64]] Add DW_CFA_AARCH64_set_ra_state stack frame operation #346

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walkerkd commented Aug 21, 2025

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walkerkd commented Jan 14, 2026

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