runtime/coverage: remove uses of //go:linkname

Move code to internal/coverage/cfile, making it possible to
access directly from testing/internal/testdeps, so that we can
avoid needing //go:linkname hacks.

For #67401.

Change-Id: I10b23a9970164afd2165e718ef3b2d9e86783883
Reviewed-on: https://go-review.googlesource.com/c/go/+/585820
Auto-Submit: Russ Cox <rsc@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Than McIntosh <thanm@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

3 files changed, 42 insertions, 5 deletions

diff --git a/src/testing/internal/testdeps/deps.go b/src/testing/internal/testdeps/deps.go
index 868307550e..88c1b253ee 100644
--- a/src/testing/internal/testdeps/deps.go
+++ b/src/testing/internal/testdeps/deps.go
@@ -13,6 +13,7 @@ package testdeps
 import (
 	"bufio"
 	"context"
+	"internal/coverage/cfile"
 	"internal/fuzz"
 	"internal/testlog"
 	"io"
@@ -26,6 +27,9 @@ import (
 	"time"
 )
 
+// Cover indicates whether coverage is enabled.
+var Cover bool
+
 // TestDeps is an implementation of the testing.testDeps interface,
 // suitable for passing to [testing.MainStart].
 type TestDeps struct{}
@@ -197,3 +201,30 @@ func (TestDeps) ResetCoverage() {
 func (TestDeps) SnapshotCoverage() {
 	fuzz.SnapshotCoverage()
 }
+
+var CoverMode string
+var Covered string
+
+func (TestDeps) InitRuntimeCoverage() (mode string, tearDown func(string, string) (string, error), snapcov func() float64) {
+	if CoverMode == "" {
+		return
+	}
+	return CoverMode, coverTearDown, cfile.Snapshot
+}
+
+func coverTearDown(coverprofile string, gocoverdir string) (string, error) {
+	var err error
+	if gocoverdir == "" {
+		gocoverdir, err = os.MkdirTemp("", "gocoverdir")
+		if err != nil {
+			return "error setting GOCOVERDIR: bad os.MkdirTemp return", err
+		}
+		defer os.RemoveAll(gocoverdir)
+	}
+	cfile.MarkProfileEmitted(true)
+	cmode := CoverMode
+	if err := cfile.ProcessCoverTestDir(gocoverdir, coverprofile, cmode, Covered, os.Stdout); err != nil {
+		return "error generating coverage report", err
+	}
+	return "", nil
+}
diff --git a/src/testing/newcover.go b/src/testing/newcover.go
index 7a70dcfffa..a7dbcfc65a 100644
--- a/src/testing/newcover.go
+++ b/src/testing/newcover.go
@@ -21,13 +21,13 @@ var cover2 struct {
 	snapshotcov func() float64
 }
 
-// registerCover2 is injected in testmain.
-//go:linkname registerCover2
-
-// registerCover2 is invoked during "go test -cover" runs by the test harness
-// code in _testmain.go; it is used to record a 'tear down' function
+// registerCover2 is invoked during "go test -cover" runs.
+// It is used to record a 'tear down' function
 // (to be called when the test is complete) and the coverage mode.
 func registerCover2(mode string, tearDown func(coverprofile string, gocoverdir string) (string, error), snapcov func() float64) {
+	if mode == "" {
+		return
+	}
 	cover2.mode = mode
 	cover2.tearDown = tearDown
 	cover2.snapshotcov = snapcov
diff --git a/src/testing/testing.go b/src/testing/testing.go
index 60f0c23137..78ad8dbaac 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -1855,6 +1855,10 @@ func (f matchStringOnly) CheckCorpus([]any, []reflect.Type) error { return nil }
 func (f matchStringOnly) ResetCoverage()                          {}
 func (f matchStringOnly) SnapshotCoverage()                       {}
 
+func (f matchStringOnly) InitRuntimeCoverage() (mode string, tearDown func(string, string) (string, error), snapcov func() float64) {
+	return
+}
+
 // Main is an internal function, part of the implementation of the "go test" command.
 // It was exported because it is cross-package and predates "internal" packages.
 // It is no longer used by "go test" but preserved, as much as possible, for other
@@ -1902,12 +1906,14 @@ type testDeps interface {
 	CheckCorpus([]any, []reflect.Type) error
 	ResetCoverage()
 	SnapshotCoverage()
+	InitRuntimeCoverage() (mode string, tearDown func(coverprofile string, gocoverdir string) (string, error), snapcov func() float64)
 }
 
 // MainStart is meant for use by tests generated by 'go test'.
 // It is not meant to be called directly and is not subject to the Go 1 compatibility document.
 // It may change signature from release to release.
 func MainStart(deps testDeps, tests []InternalTest, benchmarks []InternalBenchmark, fuzzTargets []InternalFuzzTarget, examples []InternalExample) *M {
+	registerCover2(deps.InitRuntimeCoverage())
 	Init()
 	return &M{
 		deps:        deps,