In https://github.com/NixOS/nixpkgs/issues/100119 pantheon's greeter
has g-s-d running which allows brightness controls via pkexec.
This is changed in newer versions of g-s-d (pantheon uses a fork currently),
but whenever brightness is changed with a shell of `shadow` we get
```
Oct 10 23:51:44 kirXps pkexec[18722]: lightdm: Executing command [USER=root] [TTY=unknown] [CWD=/var/lib/lightdm] [COMMAND=/run/current-system/sw/bin/elementary-settings-daemon/gsd-backlight-helper /sys/devices/pci0000:00/0000:00:02.0/drm/card0/card0-eDP-1/intel_backlight 65587]
```
I'm not sure this should be strictly needed, so we should try to
revert later on when pantheon's g-s-d is updated.
LLD: https://lld.llvm.org/
When you link a large program on a multicore machine, you can expect that LLD runs more than twice as fast as the GNU gold linker. Your mileage may vary, though.
Link-time optimization (LTO) is supported by default.
Some default settings have been tuned for the 21st century. For example, the stack is marked as non-executable by default to tighten security.
LTO & ThinLTO: https://clang.llvm.org/docs/ThinLTO.html
LTO (Link Time Optimization) achieves better runtime performance through whole-program analysis and cross-module optimization. However, monolithic LTO implements this by merging all input into a single module, which is not scalable in time or memory, and also prevents fast incremental compiles. ThinLTO is a new approach that is designed to scale like a non-LTO build, while retaining most of the performance achievement of full LTO.
PGO: https://llvm.org/docs/HowToBuildWithPGO.htmlhttps://blog.chromium.org/2020/08/chrome-just-got-faster-with-profile.html
Allows your compiler to better optimize code for how it actually runs. Users report that applying this to Clang and LLVM can decrease overall compile time by 20%.
Because PGO uses real usage scenarios that match the workflows of Chrome users around the world, the most common tasks get prioritized and made faster. Delivers up to 10% faster page loads.
CFI: https://clang.llvm.org/docs/ControlFlowIntegrity.htmlhttps://www.chromium.org/developers/testing/control-flow-integrity
Aborts the program upon detecting certain forms of undefined behavior that can potentially allow attackers to subvert the program’s control flow. These schemes have been optimized for performance, allowing developers to enable them in release builds.
By default, a program compiled with CFI will crash with SIGILL if it detects a CFI violation.
Additionally:
Use minizip instead of zlib. Chromium says zlib but actually uses minizip.
Remove old unused workarounds.
Make shell scripts POSIX compliant.
Update documentation URLs.
Prepare for using system libraries.
