cmd/link: TestLargeText in linkbig_test.go does not look right

[perillo]

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

$ go version
go version go1.16.3 linux/amd64

The TestLargeText seems to have some problems:

1. It calls os.Chdir without checking the error
2. Does not restore the original working directory
3. Calls os.Chdir later, instead of calling it early (allowing a simplification of the code)
4. Calls os.Chdir(tmpdir) twice

Here is a patch that will allow the use of the chtmpdir function (see #45182).
os.Chdir error handling and working directory restoration is not included.
It uses relative paths, since we have chdir early.

diff --git a/src/cmd/link/linkbig_test.go b/src/cmd/link/linkbig_test.go
index d5d77d6c72..e6f58a5843 100644
--- a/src/cmd/link/linkbig_test.go
+++ b/src/cmd/link/linkbig_test.go
@@ -28,6 +28,7 @@ func TestLargeText(t *testing.T) {
 	var w bytes.Buffer
 	const FN = 4
 	tmpdir := t.TempDir()
+	os.Chdir(tmpdir)
 
 	// Generate the scenario where the total amount of text exceeds the
 	// limit for the jmp/call instruction, on RISC architectures like ppc64le,
@@ -47,7 +48,7 @@ func TestLargeText(t *testing.T) {
 			fmt.Fprintf(&w, inst)
 		}
 		fmt.Fprintf(&w, "\tRET\n")
-		err := ioutil.WriteFile(tmpdir+"/"+testname+".s", w.Bytes(), 0666)
+		err := ioutil.WriteFile(testname+".s", w.Bytes(), 0666)
 		if err != nil {
 			t.Fatalf("can't write output: %v\n", err)
 		}
@@ -74,32 +75,30 @@ func TestLargeText(t *testing.T) {
 	fmt.Fprintf(&w, "\t}\n")
 	fmt.Fprintf(&w, "\tfmt.Printf(\"PASS\\n\")\n")
 	fmt.Fprintf(&w, "}")
-	err := ioutil.WriteFile(tmpdir+"/bigfn.go", w.Bytes(), 0666)
+	err := ioutil.WriteFile("bigfn.go", w.Bytes(), 0666)
 	if err != nil {
 		t.Fatalf("can't write output: %v\n", err)
 	}
 
 	// Build and run with internal linking.
-	os.Chdir(tmpdir)
 	cmd := exec.Command(testenv.GoToolPath(t), "build", "-o", "bigtext")
 	out, err := cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("Build failed for big text program with internal linking: %v, output: %s", err, out)
 	}
-	cmd = exec.Command(tmpdir + "/bigtext")
+	cmd = exec.Command("./bigtext")
 	out, err = cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("Program built with internal linking failed to run with err %v, output: %s", err, out)
 	}
 
 	// Build and run with external linking
-	os.Chdir(tmpdir)
 	cmd = exec.Command(testenv.GoToolPath(t), "build", "-o", "bigtext", "-ldflags", "'-linkmode=external'")
 	out, err = cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("Build failed for big text program with external linking: %v, output: %s", err, out)
 	}
-	cmd = exec.Command(tmpdir + "/bigtext")
+	cmd = exec.Command("./bigtext")
 	out, err = cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("Program built with external linking failed to run with err %v, output: %s", err, out)

Commenting the code that skip the test on my system (linux amd64), the test works, but I'm not sure if there was a good reason for the current implementation.

However I have found an additional issue: the test only works if GO111MODULE=off, otherwise the test fails with

Build failed for big text program with internal linking: exit status 1, output: go: go.mod file not found in current directory or any parent directory; see 'go help modules'

and all the tests that follow (when executing run.bash) fails with

cannot determine current directory: getwd: no such file or directory

[ianlancetaylor]

CC @laboger

[laboger]

I can fix the chdir stuff that doesn't look right.
This test is intended to verify very large text sections where trampolines are generated, so that only applies to ppc64x and arm64 and don't think it should be enabled for amd64 (not sure if that was your suggestion.)

I can check the module issue.

[perillo]

@laboger, no, I was not suggesting to enable it for amd64. I just forced the test to run on Linux amd64 and I got that module issue, but it is strange that the build bots don't report it.

Thanks.

[perillo]

By the way, is Chdir necessary? Isn't it better to set the exec.Cmd.Dir field to the temporary directory?

[perillo]

Here a patch to remove the use of Chdir. I have also changed the name of the executable generated using external linking, just to be sure:

diff --git a/src/cmd/link/linkbig_test.go b/src/cmd/link/linkbig_test.go
index d5d77d6c72..577fe0daae 100644
--- a/src/cmd/link/linkbig_test.go
+++ b/src/cmd/link/linkbig_test.go
@@ -14,7 +14,6 @@ import (
 	"fmt"
 	"internal/testenv"
 	"io/ioutil"
-	"os"
 	"os/exec"
 	"testing"
 )
@@ -80,26 +79,28 @@ func TestLargeText(t *testing.T) {
 	}
 
 	// Build and run with internal linking.
-	os.Chdir(tmpdir)
 	cmd := exec.Command(testenv.GoToolPath(t), "build", "-o", "bigtext")
+	cmd.Dir = tmpdir
 	out, err := cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("Build failed for big text program with internal linking: %v, output: %s", err, out)
 	}
-	cmd = exec.Command(tmpdir + "/bigtext")
+	cmd = exec.Command("./bigtext")
+	cmd.Dir = tmpdir
 	out, err = cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("Program built with internal linking failed to run with err %v, output: %s", err, out)
 	}
 
 	// Build and run with external linking
-	os.Chdir(tmpdir)
-	cmd = exec.Command(testenv.GoToolPath(t), "build", "-o", "bigtext", "-ldflags", "'-linkmode=external'")
+	cmd = exec.Command(testenv.GoToolPath(t), "build", "-o", "bigtext-ext", "-ldflags", "'-linkmode=external'")
+	cmd.Dir = tmpdir
 	out, err = cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("Build failed for big text program with external linking: %v, output: %s", err, out)
 	}
-	cmd = exec.Command(tmpdir + "/bigtext")
+	cmd = exec.Command("./bigtext-ext")
+	cmd.Dir = tmpdir
 	out, err = cmd.CombinedOutput()
 	if err != nil {
 		t.Fatalf("Program built with external linking failed to run with err %v, output: %s", err, out)

Setting Cmd.Dir when executing the generated binary is not really necessary.

[gopherbot]

Change https://golang.org/cl/308935 mentions this issue: cmd/link: fix TestLargeText