[PATCH v2 0/2] gitlab-ci.yml: Add jobs to test CFI

[Daniele Buono <dbuono@linux.vnet.ibm.com>]

For a few months now QEMU has had options to enable compiler-based
control-flow integrity if built with clang.

While this feature has a low maintenance, It's probably still better to
add tests to the CI environment to check that an update doesn't break it.

The patchset allow gitlab testing of:
* --enable-cfi: forward-edge cfi (function pointers)
* --enable-safe-stack: backward-edge cfi (return pointers)
As an added benefit, this also inherently tests LTO. 

The first patch allows a custom selection for linker parallelism.
Currently, make parallelism at build time is based on the number
of cpus available.
This doesn't work well with LTO at linking, because the linker has to
load in memory all the intermediate object files for optimization.
If the gitlab runner happens to run two linking processes at the same
time, the job will fail with an out-of-memory error,
The patch leverages the ability to maintain high parallelism at
compile time, but limit the number of linkers executed in parallel.

The second patch introduces the ci/cd jobs in the gitlab pipeline.
My original intention was to create a single chain of
build -> check -> acceptance, with all the targets compiled by default.
Unfortunately, the resulting artifact is too big and won't be uploaded.
So I split the test in two chains, that should cover all non-deprecated
targets as of today.
Build jobs are on the longer side (about 2h and 20m), but I thought it
would be better to just have 6 large jobs than tens of smaller ones.
For build, we have to select --enable-slirp=git, because CFI needs a
statically linked version of slirp, with CFI information. More info on
this can be found in a comment in .gitlab-ci.yml.

Test runs of the full pipeline are here (cfi-ci-v2 branch):
https://gitlab.com/dbuono/qemu/-/pipelines/261311362

v2:
- More details in the code about the issue of using system-wide slirp
- Use meson to only limit linker parallelism instead of forcing no
  parallelism on the whole compilation process.

Daniele Buono (2):
  gitlab-ci.yml: Allow custom # of parallel linkers
  gitlab-ci.yml: Add jobs to test CFI flags

 .gitlab-ci.yml | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 97 insertions(+)

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2.30.0