src/cmd/go/testdata/script/cgo_suspect_flag_force_external.txt

# Test case to verify that when we have a package that uses CGO in
# combination with selected "unusual" flags (involving plugins, LTO)
# that we force external linking.  See related
# issues 58619,  58620, and 58848.

[compiler:gccgo] skip # only external linking for gccgo

[!cgo] skip 'test verifies behavior that depends on CGO_CFLAGS'
[mustlinkext] skip 'test expects internal linking for non-cgo programs'

# Here we build three program: one with explicit CGO use, one with no
# CGO use, and one that uses a stdlib package ("runtime/cgo") that has
# CGO in it. It used to be that only the explicit use of CGO would
# trigger external linking, and that the program that only used
# "runtime/cgo" would always be handled with internal linking. This caused
# issues when users included odd/unusual flags (ex: -fplugin, -flto)
# in CGO_CFLAGS, causing the Go linker to have to read and interpret
# non-standard host objects.
#
# As of 1.21 we continue to use internal linking for programs whose
# CGO use comes only from stdlib packages in the absence of any flag
# funny business, however if the Go command sees flags that may be suspicious,
# it signals the Go linker to invoke the external linker.

# The next few tests run builds passing "-n" to the Go command, then
# checking the output to see if the Go command is trying to pass a
# "preferlinkext" token to the linker to request external linking.

#-----------------------

# Use a fresh GOCACHE for these next steps, so as to have the real
# actions for the runtime/cgo package appear in the "-n -x" output.
env GOCACHE=$WORK/gocache
mkdir $GOCACHE

# First build: there is no CGO in use, so no token should be present regardless
# of weird CGO flags.
go build -x -n -o dummy.exe ./noUseOfCgo
! stderr preferlinkext
env CGO_CFLAGS=-flto
go build -x -n -o dummy.exe ./noUseOfCgo
! stderr preferlinkext
env CGO_CFLAGS=

# Second build uses CGO, so we expect to see the token present in the
# -n output only when strange flags are used.
go build -x -n -o dummy.exe ./usesInternalCgo
! stderr preferlinkext
env CGO_CFLAGS=-flto
go build -x -n -o dummy.exe ./usesInternalCgo
stderr preferlinkext
env CGO_CFLAGS=-fplugin
go build -x -n -o dummy.exe ./usesInternalCgo
stderr preferlinkext
env CGO_CFLAGS=-fprofile-instr-generate
go build -x -n -o dummy.exe ./usesInternalCgo
stderr preferlinkext
env CGO_CFLAGS=

[short] skip

# In the remaining tests below we do actual builds (without -n) to
# verify that the Go linker is going the right thing in addition to the
# Go command. Here the idea is to pass "-tmpdir" to the linker, then
# check after the link is done for the presence of the file
# <tmpdir>/go.o, which the Go linker creates prior to kicking off the
# external linker.

mkdir tmp1
mkdir tmp2
mkdir tmp3
mkdir tmp4
mkdir tmp5

# First build: no external linking expected
go build -ldflags=-tmpdir=tmp1 -o $devnull ./noUseOfCgo &

# Second build: using only "runtime/cgo", expect internal linking.
go build -ldflags=-tmpdir=tmp2 -o $devnull ./usesInternalCgo &

# Third build: program uses only "runtime/cgo", so we would normally
# expect internal linking, except that cflags contain suspicious entries
# (in this case, a flag that does not appear on the allow list).
env CGO_CFLAGS=-fmerge-all-constants
env CGO_LDFLAGS=-fmerge-all-constants
go build -ldflags=-tmpdir=tmp3 -o $devnull ./usesInternalCgo &
env CGO_CFLAGS=
env CGO_LDFLAGS=

# Fourth build: explicit CGO, expect external linking.
go build -ldflags=-tmpdir=tmp4 -o $devnull ./usesExplicitCgo &

# Fifth build: explicit CGO, but we specifically asked for internal linking
# via a flag, so using internal linking it is.
[cgolinkext] go list ./usesInternalCgo
[!cgolinkext] go build '-ldflags=-tmpdir=tmp5 -linkmode=internal' -o $devnull ./usesInternalCgo &

wait

# Check first build: no external linking expected
! exists tmp1/go.o

# Check second build: using only "runtime/cgo", expect internal linking.
[!cgolinkext] ! exists tmp2/go.o
[cgolinkext] exists tmp2/go.o

# Check third build: has suspicious flag.
exists tmp3/go.o

# Fourth build: explicit CGO, expect external linking.
exists tmp4/go.o

# Fifth build: explicit CGO, -linkmode=internal.
! exists tmp5/go.o

-- go.mod --

module cgo.example

go 1.20

-- noUseOfCgo/main.go --

package main

func main() {
	println("clean as a whistle")
}

-- usesInternalCgo/main.go --

package main

import (
	"runtime/cgo"
)

func main() {
	q := "hello"
	h := cgo.NewHandle(q)
	h.Delete()
}

-- usesExplicitCgo/main.go --

package main

/*
int meaningOfLife() { return 42; }
*/
import "C"

func main() {
     println(C.meaningOfLife())
}