工具存放在哪里?

I'm having some diffculty finding out where go tools are currently located in my setup.

$ go tool
cgo
cover
vet

cover is not on the path:

$ which cover
/usr/bin/which: no cover in ...

This is the go environment:

$ go env
GOARCH="amd64"
GOBIN="~/go//bin"
GOCACHE="~/.cache/go-build"
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="~/go/"
GORACE=""
GOROOT="/usr/bin/go"
GOTMPDIR=""
GOTOOLDIR="/usr/libexec/gcc/x86_64-redhat-linux/8"
GCCGO="/usr/bin/gccgo"

And ~/go/bin is empty:

$ ls -a ~/go/
.  ..  pkg  

Where is go picking the tools from?

On my installation they're in the GOTOOLDIR in the go env output.

~% go env | grep GOTOOLDIR
GOTOOLDIR="/usr/local/Cellar/go/1.11.1/libexec/pkg/tool/darwin_amd64"
~% ls /usr/local/Cellar/go/1.11.1/libexec/pkg/tool/darwin_amd64
addr2line buildid   cover     fix       objdump   test2json
api       cgo       dist      link      pack      trace
asm       compile   doc       nm        pprof     vet