[PATCH v3] aarch64: silence GCS warnings on shared libraries for -z gcs=implicit

[Matthieu Longo]

On 20/01/2026 20:31, Alice Carlotti wrote:
> On Mon, Jan 19, 2026 at 11:56:17AM +0000, Matthieu Longo wrote:
>> Dynamic library incompatibilities should not be reported when no GCS
>> option is provided (defaults to '-z gcs=implicit') and no explicit
>> diagnostic is provided via '-z gcs-report-dynamic'.
>>
>> Binary Linux distributions do not rebuild all packages from scratch
>> when rolling out a new feature or creating a new release; only
>> modified packages get rebuilt. In the context of GCS deployment, this
>> meant that some packages were rebuilt with GCS enabled while their
>> dependencies were not yet GCS-compatible, resulting in warnings. These
>> warnings caused build failures for packages that treat linker warnings
>> as errors. Those errors slowed down the GCS deployment, and Linux
>> distribution maintainers requested that no GCS option provided should
>> be equivalent to '-z gcs=implicit -z gcs-report-dynamic=none'.
>>
>> In contrast, '-z gcs=always' should continue to report such issues by
>> default. Warnings can still be disabled or promoted to errors by
>> explicitly setting '-z gcs-report-dynamic' to respectively 'none' or
>> 'error'.
>>
>> This patch preserves the existing behaviour for '-z gcs=never', changes
>> the default behaviour of '-z gcs=implicit' or no GCS option, and removed
>> the inheritance mechanism between '-z gcs-report' and '-z gcs-report-dynamics'.
>> The expected behaviour with the different possible combinations is as
>> follows:
>> * -z gcs=never:
>>    No diagnostic messages are emitted.
>> * -z gcs=implicit:
>>    No diagnostic messages are emitted for input static objects.
>>    However, if all the input static objects are marked for GCS, the
>>    output object will also be marked for GCS.
>>    In this case the output is marked with GCS, '-z gcs-report-dynamic'
>>    defaults to 'none' and no diagnostics are emitted. Diagnostics can
>>    be enabled by explicitly providing the option.
>> * -z gcs=always:
>>    Warning diagnostics for both static and dynamic input objects are
>>    enabled by default. The two options are independent of one another,
>>    and the diagnostic level can be adjusted for each by explicitly
>>    providing the desired level to '-z gcs-report-dynamic' and '-z
>>    gcs-report'.
>>
>> The patch also updates the existing tests, removes redundant test cases,
>> and adds new tests covering cases with no report option provided, or
>> report options explicitly set.
> This patch removes all tests for mixed inputs and '-z gcs=implicit'.  I think
> it would be appropriate to retain the the old test gcs-3-b-i.d (presumably
> renamed to gcs-3-b.d with an adjusted #name) to cover this case.
> 
> OK with this change.

It looks to me that the case is already covered by gcs-2-b-iii.d
#name: '-z gcs=implicit -z gcs-report=warning' with GCS-unmarked inputs emits no warnings [shared]

The only difference is '-z gcs-report=error', but if it does not emit warnings in the first place, then there are none to turn into errors, hence my assumption that gcs-2-b-iii.d is enough.

Please, let me know if this makes sense.

Matthieu