Provide more helpful error messages when profiling is misconfigured.

This forwards the output of `runsc debug` to stderr if it fails during
a container run. Additionally, for runs with profiling enabled, it checks
the runtime arguments and prints an error if the `--profile` flag is not
found in it.

Profiling is also disabled by default on benchmarks now. This forces the
user to be explicit about where benchmarks are stored, which is less
confusing than the current behavior of empty output with no explanation
as to where the profiles are.

Fixes #10433

PiperOrigin-RevId: 642132089

Makefile

@@ -458,7 +458,8 @@ BENCHMARKS_RUNC      ?= true
 BENCHMARKS_FILTER    ?= .
 BENCHMARKS_OPTIONS   ?= -test.benchtime=30s
 BENCHMARKS_ARGS      ?= -test.v -test.bench=$(BENCHMARKS_FILTER) $(BENCHMARKS_OPTIONS)
-BENCHMARKS_PROFILE   ?= -pprof-dir=/tmp/profile -pprof-cpu -pprof-heap -pprof-block -pprof-mutex
+BENCHMARKS_PROFILE   ?=
+# Example: BENCHMARKS_PROFILE='-pprof-dir=/tmp/profile -pprof-cpu -pprof-heap -pprof-block -pprof-mutex'
 
 init-benchmark-table: ## Initializes a BigQuery table with the benchmark schema.
 	@$(call run,//tools/parsers:parser,init --project=$(BENCHMARKS_PROJECT) --dataset=$(BENCHMARKS_DATASET) --table=$(BENCHMARKS_TABLE))

pkg/test/dockerutil/dockerutil.go

@@ -124,6 +124,32 @@ func RuntimePath() (string, error) {
 	return p, nil
 }
 
+// RuntimeArgs returns the arguments for the current runtime.
+func RuntimeArgs() ([]string, error) {
+	rs, err := runtimeMap()
+	if err != nil {
+		return nil, err
+	}
+	argsAny, ok := rs["runtimeArgs"]
+	if !ok {
+		// The runtime does not have any arguments.
+		return nil, nil
+	}
+	argsAnySlice, ok := argsAny.([]any)
+	if !ok {
+		return nil, fmt.Errorf("runtime arguments should be a list of strings, got: %q (type: %T)", argsAny, argsAny)
+	}
+	args := make([]string, 0, len(argsAnySlice))
+	for i, argAny := range argsAnySlice {
+		arg, ok := argAny.(string)
+		if !ok {
+			return nil, fmt.Errorf("runtime arguments should be a list of strings, got: %q (index %d is %q which has unexpected type %T)", argsAny, i, argAny, argAny)
+		}
+		args = append(args, arg)
+	}
+	return args, nil
+}
+
 // IsGVisorRuntime returns whether the default container runtime used by
 // `dockerutil` is gVisor-based or not.
 func IsGVisorRuntime(ctx context.Context, t *testing.T) (bool, error) {

pkg/test/dockerutil/profile.go

@@ -15,11 +15,14 @@
 package dockerutil
 
 import (
+	"bytes"
 	"context"
+	"errors"
 	"fmt"
 	"os"
 	"os/exec"
 	"path/filepath"
+	"slices"
 	"time"
 
 	"golang.org/x/sys/unix"
@@ -32,10 +35,12 @@ import (
 
 // profile is for running profiles with 'runsc debug'.
 type profile struct {
-	BasePath string
-	Types    []string
-	Duration time.Duration
-	cmd      *exec.Cmd
+	BasePath    string
+	Types       []string
+	Duration    time.Duration
+	errorBuf    bytes.Buffer
+	isProfiling bool
+	cmd         *exec.Cmd
 }
 
 // profileInit initializes a profile object, if required.
@@ -86,13 +91,15 @@ func (p *profile) createProcess(c *Container) error {
 		return fmt.Errorf("failed to get root directory: %v", err)
 	}
 
-	// Format is `runsc --root=rootDir debug --profile-*=file --duration=24h containerID`.
-	args := []string{fmt.Sprintf("--root=%s", rootDir), "debug"}
+	// Format is `runsc --debug-log=/dev/stderr --root=rootDir debug --profile-*=file --duration=24h containerID`.
+	args := []string{"--debug-log=/dev/stderr", fmt.Sprintf("--root=%s", rootDir), "debug"}
 	for _, profileArg := range p.Types {
+		p.isProfiling = true
 		outputPath := filepath.Join(p.BasePath, fmt.Sprintf("%s.pprof", profileArg))
 		args = append(args, fmt.Sprintf("--profile-%s=%s", profileArg, outputPath))
 	}
 	if *trace {
+		p.isProfiling = true
 		args = append(args, fmt.Sprintf("--trace=%s", filepath.Join(p.BasePath, "sentry.trace")))
 	}
 	args = append(args, fmt.Sprintf("--duration=%s", p.Duration)) // Or until container exits.
@@ -109,7 +116,7 @@ func (p *profile) createProcess(c *Container) error {
 		time.Sleep(100 * time.Millisecond)
 	}
 	p.cmd = exec.Command(path, args...)
-	p.cmd.Stderr = os.Stderr // Pass through errors.
+	p.cmd.Stderr = &p.errorBuf
 	if err := p.cmd.Start(); err != nil {
 		return fmt.Errorf("start process failed: %v", err)
 	}
@@ -143,6 +150,28 @@ func (p *profile) Start(c *Container) error {
 func (p *profile) Stop(c *Container) error {
 	killErr := p.killProcess()
 	waitErr := p.waitProcess()
+	if waitErr != nil || killErr != nil {
+		if output := p.errorBuf.String(); output != "" {
+			fmt.Fprintf(os.Stderr, "\nprofile subcommand output:\n%s\n", output)
+			p.errorBuf.Reset()
+		}
+		if p.isProfiling {
+			runtimeArgs, err := RuntimeArgs()
+			if err != nil {
+				return fmt.Errorf("profiling failed (%v / %v) and we failed to get runtime args (%v); perhaps the runtime is not configured for profiling", killErr, waitErr, err)
+			}
+			profileEnabled := false
+			for _, possibleFlag := range []string{"-profile", "--profile", "-profile=true", "--profile=true"} {
+				if slices.Contains(runtimeArgs, possibleFlag) {
+					profileEnabled = true
+					break
+				}
+			}
+			if !profileEnabled {
+				return errors.New("runtime does not have profiling enabled, profiling will not work; either disable profiling (e.g. BENCHMARKS_PROFILE='') or add --profile=true to runtime flags")
+			}
+		}
+	}
 	if waitErr != nil && killErr != nil {
 		return killErr
 	}