It works fine for me if Curl is built with Musl Libc. I can see you're using a very cutting edge glibc. I tried reproducing this on Debian 10. The only calls that got EPERM'd were set_robust_list() and prlimit64(). I recompiled pledge.com by adding those, and Curl is still failing for reasons that aren't obvious. I've encountered issues like this in the past. Me personally I've always solved this by keeping a healthy distance from Glibc by using things like Musl and Cosmo. However I want to see Glibc users benefitting from our work too! So I'd welcome contributions from anyone who can help us do that.