1 files changed, 189 insertions, 0 deletions
diff --git a/src/internal/buildcfg/exp.go b/src/internal/buildcfg/exp.go
new file mode 100644
index 0000000..9a60253
--- /dev/null
+++ b/src/internal/buildcfg/exp.go
@@ -0,0 +1,189 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package buildcfg
+
+import (
+	"fmt"
+	"reflect"
+	"strings"
+
+	"internal/goexperiment"
+)
+
+// Experiment contains the toolchain experiments enabled for the
+// current build.
+//
+// (This is not necessarily the set of experiments the compiler itself
+// was built with.)
+//
+// experimentBaseline specifies the experiment flags that are enabled by
+// default in the current toolchain. This is, in effect, the "control"
+// configuration and any variation from this is an experiment.
+var Experiment, experimentBaseline = func() (goexperiment.Flags, goexperiment.Flags) {
+	flags, baseline, err := ParseGOEXPERIMENT(GOOS, GOARCH, envOr("GOEXPERIMENT", defaultGOEXPERIMENT))
+	if err != nil {
+		Error = err
+	}
+	return flags, baseline
+}()
+
+const DefaultGOEXPERIMENT = defaultGOEXPERIMENT
+
+// FramePointerEnabled enables the use of platform conventions for
+// saving frame pointers.
+//
+// This used to be an experiment, but now it's always enabled on
+// platforms that support it.
+//
+// Note: must agree with runtime.framepointer_enabled.
+var FramePointerEnabled = GOARCH == "amd64" || GOARCH == "arm64"
+
+// ParseGOEXPERIMENT parses a (GOOS, GOARCH, GOEXPERIMENT)
+// configuration tuple and returns the enabled and baseline experiment
+// flag sets.
+//
+// TODO(mdempsky): Move to internal/goexperiment.
+func ParseGOEXPERIMENT(goos, goarch, goexp string) (flags, baseline goexperiment.Flags, err error) {
+	regabiSupported := goarch == "amd64" && (goos == "android" || goos == "linux" || goos == "darwin" || goos == "windows")
+
+	baseline = goexperiment.Flags{
+		RegabiWrappers: regabiSupported,
+		RegabiG:        regabiSupported,
+		RegabiReflect:  regabiSupported,
+		RegabiDefer:    regabiSupported,
+		RegabiArgs:     regabiSupported,
+	}
+
+	// Start with the statically enabled set of experiments.
+	flags = baseline
+
+	// Pick up any changes to the baseline configuration from the
+	// GOEXPERIMENT environment. This can be set at make.bash time
+	// and overridden at build time.
+	if goexp != "" {
+		// Create a map of known experiment names.
+		names := make(map[string]func(bool))
+		rv := reflect.ValueOf(&flags).Elem()
+		rt := rv.Type()
+		for i := 0; i < rt.NumField(); i++ {
+			field := rv.Field(i)
+			names[strings.ToLower(rt.Field(i).Name)] = field.SetBool
+		}
+
+		// "regabi" is an alias for all working regabi
+		// subexperiments, and not an experiment itself. Doing
+		// this as an alias make both "regabi" and "noregabi"
+		// do the right thing.
+		names["regabi"] = func(v bool) {
+			flags.RegabiWrappers = v
+			flags.RegabiG = v
+			flags.RegabiReflect = v
+			flags.RegabiDefer = v
+			flags.RegabiArgs = v
+		}
+
+		// Parse names.
+		for _, f := range strings.Split(goexp, ",") {
+			if f == "" {
+				continue
+			}
+			if f == "none" {
+				// GOEXPERIMENT=none disables all experiment flags.
+				// This is used by cmd/dist, which doesn't know how
+				// to build with any experiment flags.
+				flags = goexperiment.Flags{}
+				continue
+			}
+			val := true
+			if strings.HasPrefix(f, "no") {
+				f, val = f[2:], false
+			}
+			set, ok := names[f]
+			if !ok {
+				err = fmt.Errorf("unknown GOEXPERIMENT %s", f)
+				return
+			}
+			set(val)
+		}
+	}
+
+	// regabi is only supported on amd64.
+	if goarch != "amd64" {
+		flags.RegabiWrappers = false
+		flags.RegabiG = false
+		flags.RegabiReflect = false
+		flags.RegabiDefer = false
+		flags.RegabiArgs = false
+	}
+	// Check regabi dependencies.
+	if flags.RegabiG && !flags.RegabiWrappers {
+		err = fmt.Errorf("GOEXPERIMENT regabig requires regabiwrappers")
+	}
+	if flags.RegabiArgs && !(flags.RegabiWrappers && flags.RegabiG && flags.RegabiReflect && flags.RegabiDefer) {
+		err = fmt.Errorf("GOEXPERIMENT regabiargs requires regabiwrappers,regabig,regabireflect,regabidefer")
+	}
+	return
+}
+
+// expList returns the list of lower-cased experiment names for
+// experiments that differ from base. base may be nil to indicate no
+// experiments. If all is true, then include all experiment flags,
+// regardless of base.
+func expList(exp, base *goexperiment.Flags, all bool) []string {
+	var list []string
+	rv := reflect.ValueOf(exp).Elem()
+	var rBase reflect.Value
+	if base != nil {
+		rBase = reflect.ValueOf(base).Elem()
+	}
+	rt := rv.Type()
+	for i := 0; i < rt.NumField(); i++ {
+		name := strings.ToLower(rt.Field(i).Name)
+		val := rv.Field(i).Bool()
+		baseVal := false
+		if base != nil {
+			baseVal = rBase.Field(i).Bool()
+		}
+		if all || val != baseVal {
+			if val {
+				list = append(list, name)
+			} else {
+				list = append(list, "no"+name)
+			}
+		}
+	}
+	return list
+}
+
+// GOEXPERIMENT is a comma-separated list of enabled or disabled
+// experiments that differ from the baseline experiment configuration.
+// GOEXPERIMENT is exactly what a user would set on the command line
+// to get the set of enabled experiments.
+func GOEXPERIMENT() string {
+	return strings.Join(expList(&Experiment, &experimentBaseline, false), ",")
+}
+
+// EnabledExperiments returns a list of enabled experiments, as
+// lower-cased experiment names.
+func EnabledExperiments() []string {
+	return expList(&Experiment, nil, false)
+}
+
+// AllExperiments returns a list of all experiment settings.
+// Disabled experiments appear in the list prefixed by "no".
+func AllExperiments() []string {
+	return expList(&Experiment, nil, true)
+}
+
+// UpdateExperiments updates the Experiment global based on a new GOARCH value.
+// This is only required for cmd/go, which can change GOARCH after
+// program startup due to use of "go env -w".
+func UpdateExperiments(goos, goarch, goexperiment string) {
+	var err error
+	Experiment, experimentBaseline, err = ParseGOEXPERIMENT(goos, goarch, goexperiment)
+	if err != nil {
+		Error = err
+	}
+}