With a quick look, it seems "net" is not the only pkg which depends on
cgo, though by default it uses pure Go DNS resolver only.
I tested on small program:
package main
import (
"fmt"
"net/http"
)
func main() {
fmt.Println("Hello, playground")
http.ListenAndServe(":9999", nil)
}
Which is dynamically linked if CGO_ENABLED=1 is set, and statically linked
if CGO_ENABLED=0 is set, irrespective of GODEBUG=netdns=go .
Diffing the cgo symbols from ELFs from the 2 cases shows that enabling cgo
adds 61 more functions:
_cgo_b0c710f30cfd_C2func_
_cgo_b0c710f30cfd_C2func_
_cgo_b0c710f30cfd_Cfunc__
_cgo_b0c710f30cfd_Cfunc_f
_cgo_b0c710f30cfd_Cfunc_f
_cgo_b0c710f30cfd_Cfunc_g
_cgo_b0c710f30cfd_Cfunc_g
_cgo_b0c710f30cfd_Cfunc_g
cgo_context_function
_cgo_get_context_function
_cgo_panic
_cgo_panic
_cgo_release_context
_cgo_sys_thread_start
_cgo_topofstack
_cgo_topofstack
_cgo_try_pthread_create
_cgo_wait_runtime_init_do
net._cgo_b0c710f30cfd_C2f
net._cgo_b0c710f30cfd_Cfu
net._cgo_b0c710f30cfd_Cfu
net._cgo_b0c710f30cfd_Cfu
net._cgo_b0c710f30cfd_Cfu
net._cgo_cmalloc
net.cgoIPLookup
net.cgoLookupIP
net.cgoLookupIPCNAME
net.cgoLookupIPCNAME.func
net.cgoLookupIPCNAME.func
net.cgoLookupIPCNAME.func
net.cgoLookupPort
net.cgoLookupServicePort
net.cgoLookupServicePort.
net.cgoLookupServicePort.
net.cgoLookupServicePort.
net.cgoPortLookup
runtime.cgoAlwaysFalse
runtime/cgo(.bss)
runtime.cgocallback
runtime.cgoCheckArg
runtime.cgoCheckPointer
runtime.cgoCheckUnknownPo
runtime._cgo_panic_intern
runtime/cgo(.rodata)
runtime/cgo(.rodata.str1.
runtime/cgo(.rodata.str1.
runtime/cgo(.text)
runtime.cgoUse
x_cgo_callers
x_cgo_init
x_cgo_inittls
x_cgo_mmap
x_cgo_munmap
x_cgo_notify_runtime_init
x_cgo_set_context_functio
x_cgo_setenv
x_cgo_sigaction
x_cgo_sys_thread_create
x_cgo_threadentry
x_cgo_thread_start
x_cgo_unsetenv
Here we can see "net" is not the only pkg that uses CGO, but runtime uses
it as well.
These can be explored to understand more.
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