[PATCH] arm64/scs: Fix handling of advance_loc4

[Ard Biesheuvel]

On Thu, 12 Mar 2026, at 14:59, Will Deacon wrote:
> [+Ard]
>
> On Tue, Mar 10, 2026 at 03:15:56PM +0100, Pepper Gray wrote:
>> DW_CFA_advance_loc4 is defined but no handler is implemented. Its
>> CFA opcode defaults to EDYNSCS_INVALID_CFA_OPCODE triggering an
>> error which wrongfully prevents modules from loading.
>
> Can you provide some instructions for reproducing this, please? For
> example, which toolchain you are using and which module are you building?
>
>> Signed-off-by: Pepper Gray <hello at peppergray.xyz>
>> ---
>>  arch/arm64/kernel/pi/patch-scs.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>> 
>> diff --git a/arch/arm64/kernel/pi/patch-scs.c b/arch/arm64/kernel/pi/patch-scs.c
>> index bbe7d30ed12b32..dac568e4a54f23 100644
>> --- a/arch/arm64/kernel/pi/patch-scs.c
>> +++ b/arch/arm64/kernel/pi/patch-scs.c
>> @@ -192,6 +192,14 @@ static int scs_handle_fde_frame(const struct
>> eh_frame *frame,
>>   size -= 2;
>>   break;
>> 
>> + case DW_CFA_advance_loc4:
>> + loc += *opcode++ * code_alignment_factor;
>> + loc += (*opcode++ << 8) * code_alignment_factor;
>> + loc += (*opcode++ << 16) * code_alignment_factor;
>> + loc += (*opcode++ << 24) * code_alignment_factor;
>> + size -= 4;
>> + break;

The logic looks sound to me, although I'd also be interested in understanding under which circumstances these are emitted.