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// 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"
"internal/goexperiment"
"reflect"
"strings"
)
// 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
}
baseline := goexperiment.Flags{
RegabiWrappers: regabiSupported,
RegabiArgs: regabiSupported,
CoverageRedesign: 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, 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)
}
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