1 files changed, 194 insertions, 0 deletions
diff --git a/src/internal/buildcfg/exp.go b/src/internal/buildcfg/exp.go
new file mode 100644
index 0000000..a45cfaf
--- /dev/null
+++ b/src/internal/buildcfg/exp.go
@@ -0,0 +1,194 @@
+// 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"
+)
+
+// ExperimentFlags represents a set of GOEXPERIMENT flags relative to a baseline
+// (platform-default) experiment configuration.
+type ExperimentFlags struct {
+	goexperiment.Flags
+	baseline goexperiment.Flags
+}
+
+// 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 ExperimentFlags = func() ExperimentFlags {
+	flags, err := ParseGOEXPERIMENT(GOOS, GOARCH, envOr("GOEXPERIMENT", defaultGOEXPERIMENT))
+	if err != nil {
+		Error = err
+		return ExperimentFlags{}
+	}
+	return *flags
+}()
+
+// DefaultGOEXPERIMENT is the embedded default GOEXPERIMENT string.
+// It is not guaranteed to be canonical.
+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) (*ExperimentFlags, error) {
+	// regabiSupported is set to true on platforms where register ABI is
+	// supported and enabled by default.
+	// regabiAlwaysOn is set to true on platforms where register ABI is
+	// always on.
+	var regabiSupported, regabiAlwaysOn bool
+	switch goarch {
+	case "amd64", "arm64", "ppc64le", "ppc64", "riscv64":
+		regabiAlwaysOn = true
+		regabiSupported = true
+	case "loong64":
+		regabiSupported = true
+	}
+
+	baseline := goexperiment.Flags{
+		RegabiWrappers:   regabiSupported,
+		RegabiArgs:       regabiSupported,
+		CoverageRedesign: true,
+		AllocHeaders:     true,
+		ExecTracer2:      true,
+	}
+
+	// Start with the statically enabled set of experiments.
+	flags := &ExperimentFlags{
+		Flags:    baseline,
+		baseline: 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.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.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.Flags = goexperiment.Flags{}
+				continue
+			}
+			val := true
+			if strings.HasPrefix(f, "no") {
+				f, val = f[2:], false
+			}
+			set, ok := names[f]
+			if !ok {
+				return nil, fmt.Errorf("unknown GOEXPERIMENT %s", f)
+			}
+			set(val)
+		}
+	}
+
+	if regabiAlwaysOn {
+		flags.RegabiWrappers = true
+		flags.RegabiArgs = true
+	}
+	// regabi is only supported on amd64, arm64, loong64, riscv64, ppc64 and ppc64le.
+	if !regabiSupported {
+		flags.RegabiWrappers = false
+		flags.RegabiArgs = false
+	}
+	// Check regabi dependencies.
+	if flags.RegabiArgs && !flags.RegabiWrappers {
+		return nil, fmt.Errorf("GOEXPERIMENT regabiargs requires regabiwrappers")
+	}
+	return flags, nil
+}
+
+// String returns the canonical GOEXPERIMENT string to enable this experiment
+// configuration. (Experiments in the same state as in the baseline are elided.)
+func (exp *ExperimentFlags) String() string {
+	return strings.Join(expList(&exp.Flags, &exp.baseline, false), ",")
+}
+
+// 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
+}
+
+// Enabled returns a list of enabled experiments, as
+// lower-cased experiment names.
+func (exp *ExperimentFlags) Enabled() []string {
+	return expList(&exp.Flags, nil, false)
+}
+
+// All returns a list of all experiment settings.
+// Disabled experiments appear in the list prefixed by "no".
+func (exp *ExperimentFlags) All() []string {
+	return expList(&exp.Flags, nil, true)
+}