cmd/go: cache results of exec.LookPath

[Zyxon123]

What version of Go are you using (go version)?

$ go version
go version go1.13.6 windows/amd64

Does this issue reproduce with the latest release?

What operating system and processor architecture are you using (go env)?

• windows 10 64 bit version 1809
• intel i5-8265U

go env Output

$ go env
set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\lidic\AppData\Local\go-build
set GOENV=C:\Users\lidic\AppData\Roaming\go\env
set GOEXE=.exe
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\lidic\go
set GOPRIVATE=
set GOPROXY=https://proxy.golang.org,direct
set GOROOT=c:\go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLDIR=c:\go\pkg\tool\windows_amd64
set GCCGO=gccgo
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=C:\Go\src\go.mod
set CGO_CFLAGS=-g -O2
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-g -O2
set CGO_FFLAGS=-g -O2
set CGO_LDFLAGS=-g -O2
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=C:\Users\lidic\AppData\Local\Temp\go-build756524190=/tmp/go-build -gno-record-gcc-switches
GOROOT/bin/go version: go version go1.13.6 windows/amd64
GOROOT/bin/go tool compile -V: compile version go1.13.6

What did you do?

Hi,

I followed the steps here after I installed Go. However, running go run hello.go takes around 10 - 20 seconds for it to output “hello, world”. Same thing with go build. I’ve also tried reinstalling and excluding my Go folder and Go temp folder from windows defender (the only antivirus I use). I've even disabled real time protection. How do I fix this? Any help is appreciated.

Thanks!

What did you expect to see?

I expect a hello world program to be compiled within seconds, other users are able to do so.

What did you see instead?

Takes 10-20 seconds to compile instead.

PS C:\Go\src\hello> Measure-Command {go run hello.go}


Days              : 0
Hours             : 0
Minutes           : 0
Seconds           : 15
Milliseconds      : 582
Ticks             : 155821163
TotalDays         : 0.000180348568287037
TotalHours        : 0.00432836563888889
TotalMinutes      : 0.259701938333333
TotalSeconds      : 15.5821163
TotalMilliseconds : 15582.1163

go run -x output

C:\Go\src\hello>go run -x hello.go
WORK=C:\Users\lidic\AppData\Local\Temp\go-build803697114
mkdir -p $WORK\b001\
cat >$WORK\b001\importcfg.link << 'EOF' # internal
packagefile command-line-arguments=C:\Users\lidic\AppData\Local\go-build\a8\a8c4809a5f80405952f1e99a0a10c35826595987039565f2c4eed84d206e5060-d
packagefile fmt=c:\go\pkg\windows_amd64\fmt.a
packagefile runtime=c:\go\pkg\windows_amd64\runtime.a
packagefile errors=c:\go\pkg\windows_amd64\errors.a
packagefile internal/fmtsort=c:\go\pkg\windows_amd64\internal\fmtsort.a
packagefile io=c:\go\pkg\windows_amd64\io.a
packagefile math=c:\go\pkg\windows_amd64\math.a
packagefile os=c:\go\pkg\windows_amd64\os.a
packagefile reflect=c:\go\pkg\windows_amd64\reflect.a
packagefile strconv=c:\go\pkg\windows_amd64\strconv.a
packagefile sync=c:\go\pkg\windows_amd64\sync.a
packagefile unicode/utf8=c:\go\pkg\windows_amd64\unicode\utf8.a
packagefile internal/bytealg=c:\go\pkg\windows_amd64\internal\bytealg.a
packagefile internal/cpu=c:\go\pkg\windows_amd64\internal\cpu.a
packagefile runtime/internal/atomic=c:\go\pkg\windows_amd64\runtime\internal\atomic.a
packagefile runtime/internal/math=c:\go\pkg\windows_amd64\runtime\internal\math.a
packagefile runtime/internal/sys=c:\go\pkg\windows_amd64\runtime\internal\sys.a
packagefile internal/reflectlite=c:\go\pkg\windows_amd64\internal\reflectlite.a
packagefile sort=c:\go\pkg\windows_amd64\sort.a
packagefile sync/atomic=c:\go\pkg\windows_amd64\sync\atomic.a
packagefile math/bits=c:\go\pkg\windows_amd64\math\bits.a
packagefile internal/oserror=c:\go\pkg\windows_amd64\internal\oserror.a
packagefile internal/poll=c:\go\pkg\windows_amd64\internal\poll.a
packagefile internal/syscall/windows=c:\go\pkg\windows_amd64\internal\syscall\windows.a
packagefile internal/testlog=c:\go\pkg\windows_amd64\internal\testlog.a
packagefile syscall=c:\go\pkg\windows_amd64\syscall.a
packagefile time=c:\go\pkg\windows_amd64\time.a
packagefile unicode/utf16=c:\go\pkg\windows_amd64\unicode\utf16.a
packagefile unicode=c:\go\pkg\windows_amd64\unicode.a
packagefile internal/race=c:\go\pkg\windows_amd64\internal\race.a
packagefile internal/syscall/windows/sysdll=c:\go\pkg\windows_amd64\internal\syscall\windows\sysdll.a
packagefile internal/syscall/windows/registry=c:\go\pkg\windows_amd64\internal\syscall\windows\registry.a
EOF
mkdir -p $WORK\b001\exe\
cd .
"c:\\go\\pkg\\tool\\windows_amd64\\link.exe" -o "C:\\Users\\lidic\\AppData\\Local\\Temp\\go-build803697114\\b001\\exe\\hello.exe" -importcfg "C:\\Users\\lidic\\AppData\\Local\\Temp\\go-build803697114\\b001\\importcfg.link" -s -w -buildmode=exe -buildid=boKU76zxCBTD9TQHu-ws/-9UkAzfu17Kq0_a_DtT8/N9PQnONczWnG7Jk1PdaH/boKU76zxCBTD9TQHu-ws -extld=gcc "C:\\Users\\lidic\\AppData\\Local\\go-build\\a8\\a8c4809a5f80405952f1e99a0a10c35826595987039565f2c4eed84d206e5060-d"
$WORK\b001\exe\hello.exe
hello, world

go run (timing)

It may be of interest to the Golang developers to check the timing of other available downloads.

go1.13.6.linux-386.tar.gz

bash-4.3$ uname -mp                             
i686 Intel(R) Atom(TM) CPU N270   @ 1.60GHz
bash-4.3$ free --giga | perl -lae 'print @F[0,1] if $. == 2'
Mem:1
bash-4.3$ export PATH=/usr/local/go/bin:${PATH}
bash-4.3$ mkdir -p ~/go/src/hello
bash-4.3$ cat << EOF | gofmt > ~/go/src/hello/hello.go
> package main
> 
> import "fmt"
> 
> func main() {
> fmt.Printf("hello, world\n")
> }
> EOF
bash-4.3$ /usr/bin/time -p go run ~/go/src/hello/hello.go
hello, world
real 2.33
user 1.59
sys 0.31
bash-4.3$ rm -r ~/.cache/go-build
bash-4.3$ $PLAN9/bin/time go run ~/go/src/hello/hello.go
hello, world
1.57u 0.35s 1.86r 	 go run /home/eric/go/src/hello/hello.go
bash-4.3$ file /usr/local/go/bin/go
/usr/local/go/bin/go: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ld-linux.so.2, Go BuildID=bVwMwAdXBpYp4PBvIrqZ/vbfX15UF6cgq3THigMUx/QSxQRVWmK-8uFUlegS1A/TD0XQ0eQXwJkvrDVR_B1, not stripped
bash-4.3$ rm -r ~/.cache/go-build
bash-4.3$

Stripping the files from go1.13.6.linux-386.tar.gz the time is slightly different.

GNU 1.7
real 2.23
user 1.49
sys 0.36

Plan 9 from User Space
1.58u 0.31s 1.81r

[ianlancetaylor]

You didn't fill out the issue template. What is the output of go env?

Also, what is the output of go run -x hello.go?

[Zyxon123]

You didn't fill out the issue template. What is the output of go env?

Also, what is the output of go run -x hello.go?

Ok I've updated my post

[ianlancetaylor]

Thanks. Unfortunately I still don't see why it is so slow.

What is the output of go build -ldflags=-v hello.go?

Since this is Windows, the problem may be due to a virus checker.

[Zyxon123]

Thanks. Unfortunately I still don't see why it is so slow.

What is the output of go build -ldflags=-v hello.go?

Since this is Windows, the problem may be due to a virus checker.

Here's the output:

PS C:\go\src\hello> go build -ldflags=-v hello.go
# command-line-arguments
HEADER = -H11 -T0xffffffffffffffff -R0xffffffff
 0.00 deadcode
 0.01 symsize = 0
 0.08 pclntab=460347 bytes, funcdata total 109854 bytes
 0.09 dodata
 0.09 dwarf
 0.12 reloc
 0.12 asmb
 0.12 codeblk
 0.12 rodatblk
 0.13 datblk
 0.13 sym
 0.13 dwarf
 0.13 headr
 0.13 symsize = 0
 0.13 cpu time
53707 symbols
63284 liveness data

[ianlancetaylor]

Thanks. I was wondering if it were using external linking, but it's not.

I have no explanation other than possibly a virus checker. Sorry.

The go.exe env output lists GOPATH=C:\Users\lidic\go.

From your update it looks like C:\Go\src\hello is where your source file is.

I installed Golang only once on Windows 10 (64-bit).

I downloaded a go1.xx.x.windows-amd64.zip file, extracted it, opened an elevated command prompt and moved it to C:\.

Next I disabled via the context menu indexing for C:\go.

Does locating hello.go in C:\Users\lidic\go\src\hello make any difference?

[Zyxon123]

The go.exe env output lists GOPATH=C:\Users\lidic\go.

From your update it looks like C:\Go\src\hello is where your source file is.

I installed Golang only once on Windows 10 (64-bit).

I downloaded a go1.xx.x.windows-amd64.zip file, extracted it, opened an elevated command prompt and moved it to C:\.

Next I disabled via the context menu indexing for C:\go.

Does locating hello.go in C:\Users\lidic\go\src\hello make any difference?

I moved hello.go to C:\Users\lidic\go\src\hello and it made no difference. I also changed my GOPATH to C:\Go and it made no difference too.

I received a reply to an e-mail I sent to Redmond.

Doesn't look like it's specific to AV/Defender.

The way you rule out (or in) Defender is to temporarily disable it, do the compile, and then compare on vs off times. Looks like they've done that, though.

#36768 (comment).

The root of the Go tree cannot be included as a value in the Go path.

[proyb6]

I'm not using Windows, my assumption if did you have made any Windows performance tuning e.g. disable timestamp or etc?

[Zyxon123]

I'm not using Windows, my assumption if did you have made any Windows performance tuning e.g. disable timestamp or etc?

No. I am able to reproduce this behaviour on another PC that is also windows 10 with i7.

[0intro]

@Zyxon123 asked me to provide the time measurements on Plan 9 for reference.

% go version
go version go1.13.6 plan9/386
% time go run hello.go
hello, world
0.04u 0.25s 0.77r 	 go run hello.go