Armv8.3+ capable CPUs might segfault with incorrect compilation options.
See related upstream report: https://bugs.ruby-lang.org/issues/20085
We have hit this on COPR which uses [0] c7g.xlarge AWS flavor for aarch64
architecture builds. This machine flavor seems to fall into the ARMv8.3+
range.
Fedora CFLAGS come with `-mbranch-protection=standard` which means that
both BTI and the PAC protections are used. The option is equivalent
to `-mbranch-protection=pac-ret+bti`.
However, since the upstream configure.ac automatically appends
`-mbranch-protection=pac-ret`, the BTI protection is not used
as the last used option seems to overwrite [1] the Fedora
default for this.
To resolve both of these issues, of BTI being skipped and the potential
segfaults a patch is applied.
To fix segfaults an upstream patch was applied [2].
To fix the issue of overridden option I have patched the
configure.ac file to check for the `=standard` first when searching for a usable
`-mbranch-protection` option.
The overriding of our options was reported upstream:
<https://bugs.ruby-lang.org/issues/20154>
In the same issue I provided the extension of compilation option as an
attachment, to showcase a workaround that fixes the situation in Fedora.
[0] <https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/Y4GPCGQAZT2LJ5CE7MTIEFKGAPP6O2DW/>
[1] <https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/QWLEBS4YQH73HJNNLKCCGIIOU3SSXAYK/>
[2] <02973b78f4>
