c-gull re-exports libc's API, so it can be used as a drop-in replacement.
This line:
libc = { path = "../../c-gull", features = ["coexist-with-libc"], package = "c-gull" }tells cargo to use c-gull in place of libc. In this configuration, it coexists
with the system libc and doesn't replace the malloc, pthread, or getauxval
functions, but it replaces everything else that it can, such as the getuid
and getgid functions in the example.