[Bug default/28954] New: add Linux Kernel symbol namespace support

["gprocida at google dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=28954

            Bug ID: 28954
           Summary: add Linux Kernel symbol namespace support
           Product: libabigail
           Version: unspecified
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: default
          Assignee: dodji at redhat dot com
          Reporter: gprocida at google dot com
                CC: libabigail at sourceware dot org
  Target Milestone: ---

Hi.

We have started to see Linux kernel symbol namespace changes break module
loading, without being picked up by ABI monitoring beforehand.

If a symbol has a namespace, then any module attempting to use it (run-time
load check) must have imported (compile-time) the namespace. Load failure can
be commuted to a warning but I doubt we would do that for Android.

In terms of ABI monitoring, a change to a symbol's namespace should be reported
as an ABI diff.

While it might also be nice to store the imported namespaces per module (at the
abg-corpus level), without also tracking undefined symbols this wouldn't allow
any automatic checking of kernel / module compatibility. Also, there is a
compile-time check that does that anyway. We are trying to ensure that
separately built kernel and modules will (continue to) work together.

At a minimum we need the following:

* new ELF symbol XML attribute (and possible documentation update)
* new field in ELF symbol
* symtab reader changes to populate this
* XML writer change to print this
* XML reader change to read this
* categorisation of symbol namespace changes (probably the same as for CRCs)
* symbol namespace diff generation / reporting

I'm happy to start work on this, but would welcome any early feedback.

References

https://www.kernel.org/doc/html/latest/core-api/symbol-namespaces.html
https://lwn.net/Articles/760045/
https://lpc.events/event/2/contributions/220/attachments/44/51/01._Symbol_Namespaces__Plumbers_v2.pdf

Giuliano.

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