[Development] Qt patches to support AArch64 architecture

[Dmitry Shachnev]

Lars: this mail needs your attention.

Hi,

AArch64 is a new 64-bit ARM architecture, that will be used in a big range of devices,
from servers to iPhones. See this Wikipedia article for details:
https://en.wikipedia.org/wiki/ARM_architecture#64.2F32-bit_architecture

In Debian/Ubuntu, we have been working to enable AArch64 (aka ARM64) support for Qt
packages. We would like to forward those patches upstream.

Please see https://bugs.debian.org/735488 for the full discussion and
https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=200;bug=735488 for the patches.

We understand that these patches might be seen as a new feature for Qt4, but the
reality is that they will get applied on all distributions wanting to support arm64, so
it's better to have them upstreamed.

Let me describe the current situation and patches briefly:

**Patches already applied in Git**:
[qtbase] https://qt.gitorious.org/qt/qtbase/commit/410e9cd5b1a6eb87 (basic detection)
[qtscript] https://qt.gitorious.org/qt/qtscript/commit/2e049836ee16f4ae (JavaScriptCore support)

**Cherry-pick waiting for approval**:
[qt4] https://codereview.qt-project.org/79602 (JavaScriptCore support)

**Marcin Juszkiewicz’s patches (licensed under either Public Domain or BSD)**:
[qt4] basic-aarch64-detection.patch [done differently to what was done in qtbase]
[qt4] mkspecs.patch (mkspecs for qt4)
[qtbase and qt4] syscalls.patch (inotify syscalls numbers)

**Mark Salter’s patch (licensed under BSD)**:
[qt4] qatomic.patch (atomics for qt4)

The first issue comes with Marcin’s and Mark’s patches. They are RedHat
employees, and they cannot sign the CLA. So we asked them to put the patches
under a license which could enable us to merge the patches upstream. Marcin
agreed to license his patches under CC0 (aka Public Domain) or simply BSD
licensed [0], and Mark under the BSD license [1].

[0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=735488#179
[1] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=735488#195

The second issue is that Qt may require, only for arm64, -fpermissive to build.
This could mean that something is not really finished, but it will get certainly
ironed out with some time.

Finally we Debian maintainers are not able to verify the patches ourselves
*yet*, as we don’t have access to porterboxes. So far only Debian arm64 porters
have access. Non the less, patches are already applied in Ubuntu (and most
probably Red Hat too, as the patches come from them), and the current Qt 4
packages built fine there. If you want testers for the patches, try asking
Marcin or Wookey (CCed), they should be able to help you.

I am going to submit the missing patches to Gerrit if you have nothing against
that.

Kind regards,

--
Dmitry Shachnev (on behalf on Debian Qt maintainers)
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