It's not a syscall, it's a C standard library function that may read files, talk to dbus, read env vars, etc. The problem is people quite understandably expect its re-entrancy to mean more than it really means.

Oh, that's my error. Shows you how much code I write that calls into libc, i.e. almost none.

If you write anything other than Go or Zig on Linux, you're probably calling libc without realising.

Obviously. But I meant directly writing the code that calls into libc myself.

a "syscall" is not going to call back into your code to get the environment. If a "syscall" is using your environment, it's part of your code, probably better described as a library call.

Few people make raw syscalls.