HN user
If you are copy and pasting code from open source projects into your own project, then I think that is more likely to be considered copyright infringement than fair use. Fair use is generally for things like criticism, parody, teaching etc. Obviously this kind of thing would need to be judged on a case-by-case basis, but I think you are on shaky ground here.
I put the benchmark into quick-bench but could not replicate the 40% result. The sentinel version was faster but only slightly.
https://quick-bench.com/q/314Z81FskTlcDqMCUHFVhWmDz8Q
Update 1: After moving some constants around, I get the 40% result:
https://quick-bench.com/q/lPrpQTAyDQuOoKS9MBWCTBXk1TE
No idea why it made such a big difference to the benchmark.
Update 2: If the test order is reversed, the result goes back to being only slightly faster for the sentinel version:
The snoop command on SunOS and IRIX had it in the 90s too.
If you are using gcc you can use the -Wparentheses flag to turn on warnings for this: https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html#inde...
I once worked in an office with fake windows---just some blinds hung over a small recess in the wall.
When our team first arrived in the office, a colleague walked over to them and said something along the lines of `let's get some sunlight in here' before opening them to reveal the deception.
This page [1] describes additional tuning parameters. In particular adjusting /proc/sys/kernel/sched_rt_runtime_us can be beneficial.
[1] https://access.redhat.com/documentation/en-us/red_hat_enterp...
Currently the page must be writeable at some point in order to create the trampoline.
A page fault is used as a way of executing the trampoline without the page having to be made executable/writable---the page fault handler recognises the page as a special trampoline page and handles the jump to the trampolines target address (which was previously registered using the new syscall).
Note that AFAICS this is unrelated to Spectre. The intended use is for constructing closures for use in FFI libraries such as libffi.
EDIT: I think I perhaps misunderstood your query---are you saying why not just make a system call where the kernel creates the page for you with the desired trampoline code and execute permissions?
Would you mind sharing which course you took please? It sounds very interesting.
See also GWP-ASan: http://llvm.org/docs/GwpAsan.html