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

[Matthieu Longo]

On 21/01/2026 11:16, Alice Carlotti wrote:
> On Wed, Jan 21, 2026 at 10:46:59AM +0000, Matthieu Longo wrote:
>> 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]
> 
> If I've read it correctly, none of the inputs to the new gcs-2-b-iii.d have GCS
> markings.  What I'm looking for is a test where some, but not all, of the
> inputs have GCS markings (to verify that the logic for -z gcs=implicit is
> checking that all of the inputs are marked, as opposed to checking that any of
> them are marked).
> 

It makes sense now. Thanks for noticing this.
I added the test case.

Matthieu