Add introspection for Linux/AMD64 syscalls

Adds simple introspection for syscall compatibility information to Linux/AMD64.
Syscalls registered in the syscall table now have associated metadata like
name, support level, notes, and URLs to relevant issues.

Syscall information can be exported as a table, JSON, or CSV using the new
'runsc help syscalls' command. Users can use this info to debug and get info
on the compatibility of the version of runsc they are running or to generate
documentation.

PiperOrigin-RevId: 252558304

4 files changed, 479 insertions, 1 deletions

diff --git a/runsc/cmd/BUILD b/runsc/cmd/BUILD
index 173b7671e..df6af0ced 100644
--- a/runsc/cmd/BUILD
+++ b/runsc/cmd/BUILD
@@ -18,6 +18,7 @@ go_library(
         "events.go",
         "exec.go",
         "gofer.go",
+        "help.go",
         "kill.go",
         "list.go",
         "path.go",
@@ -29,6 +30,7 @@ go_library(
         "spec.go",
         "start.go",
         "state.go",
+        "syscalls.go",
         "wait.go",
     ],
     importpath = "gvisor.googlesource.com/gvisor/runsc/cmd",
@@ -39,6 +41,7 @@ go_library(
         "//pkg/log",
         "//pkg/p9",
         "//pkg/sentry/control",
+        "//pkg/sentry/kernel",
         "//pkg/sentry/kernel/auth",
         "//pkg/unet",
         "//pkg/urpc",
diff --git a/runsc/cmd/help.go b/runsc/cmd/help.go
new file mode 100644
index 000000000..ff4f901cb
--- /dev/null
+++ b/runsc/cmd/help.go
@@ -0,0 +1,126 @@
+// Copyright 2018 Google LLC
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cmd
+
+import (
+	"context"
+	"fmt"
+
+	"flag"
+	"github.com/google/subcommands"
+)
+
+// NewHelp returns a help command for the given commander.
+func NewHelp(cdr *subcommands.Commander) *Help {
+	return &Help{
+		cdr: cdr,
+	}
+}
+
+// Help implements subcommands.Command for the "help" command. The 'help'
+// command prints help for commands registered to a Commander but also allows for
+// registering additional help commands that print other documentation.
+type Help struct {
+	cdr      *subcommands.Commander
+	commands []subcommands.Command
+	help     bool
+}
+
+// Name implements subcommands.Command.Name.
+func (*Help) Name() string {
+	return "help"
+}
+
+// Synopsis implements subcommands.Command.Synopsis.
+func (*Help) Synopsis() string {
+	return "Print help documentation."
+}
+
+// Usage implements subcommands.Command.Usage.
+func (*Help) Usage() string {
+	return `help [<subcommand>]:
+	With an argument, prints detailed information on the use of
+	the specified topic or subcommand. With no argument, print a list of
+	all commands and a brief description of each.
+`
+}
+
+// SetFlags implements subcommands.Command.SetFlags.
+func (h *Help) SetFlags(f *flag.FlagSet) {}
+
+// Execute implements subcommands.Command.Execute.
+func (h *Help) Execute(ctx context.Context, f *flag.FlagSet, args ...interface{}) subcommands.ExitStatus {
+	switch f.NArg() {
+	case 0:
+		fmt.Fprintf(h.cdr.Output, "Usage: %s <flags> <subcommand> <subcommand args>\n\n", h.cdr.Name())
+		fmt.Fprintf(h.cdr.Output, `runsc is a command line client for running applications packaged in the Open
+Container Initiative (OCI) format. Applications run by runsc are run in an
+isolated gVisor sandbox that emulates a Linux environment.
+
+gVisor is a user-space kernel, written in Go, that implements a substantial
+portion of the Linux system call interface. It provides an additional layer
+of isolation between running applications and the host operating system.
+
+Functionality is provided by subcommands. For additonal help on individual
+subcommands use "%s %s <subcommand>".
+
+`, h.cdr.Name(), h.Name())
+		h.cdr.VisitGroups(func(g *subcommands.CommandGroup) {
+			h.cdr.ExplainGroup(h.cdr.Output, g)
+		})
+
+		fmt.Fprintf(h.cdr.Output, "Additional help topics (Use \"%s %s <topic>\" to see help on the topic):\n", h.cdr.Name(), h.Name())
+		for _, cmd := range h.commands {
+			fmt.Fprintf(h.cdr.Output, "\t%-15s  %s\n", cmd.Name(), cmd.Synopsis())
+		}
+		fmt.Fprintf(h.cdr.Output, "\nUse \"%s flags\" for a list of top-level flags\n", h.cdr.Name())
+		return subcommands.ExitSuccess
+	default:
+		// Look for commands registered to the commander and print help explanation if found.
+		found := false
+		h.cdr.VisitCommands(func(g *subcommands.CommandGroup, cmd subcommands.Command) {
+			if f.Arg(0) == cmd.Name() {
+				h.cdr.ExplainCommand(h.cdr.Output, cmd)
+				found = true
+			}
+		})
+		if found {
+			return subcommands.ExitSuccess
+		}
+
+		// Next check commands registered to the help command.
+		for _, cmd := range h.commands {
+			if f.Arg(0) == cmd.Name() {
+				fs := flag.NewFlagSet(f.Arg(0), flag.ContinueOnError)
+				fs.Usage = func() { h.cdr.ExplainCommand(h.cdr.Error, cmd) }
+				cmd.SetFlags(fs)
+				if fs.Parse(f.Args()[1:]) != nil {
+					return subcommands.ExitUsageError
+				}
+				return cmd.Execute(ctx, f, args...)
+			}
+		}
+
+		fmt.Fprintf(h.cdr.Error, "Subcommand %s not understood\n", f.Arg(0))
+	}
+
+	f.Usage()
+	return subcommands.ExitUsageError
+}
+
+// Register registers a new help command.
+func (h *Help) Register(cmd subcommands.Command) {
+	h.commands = append(h.commands, cmd)
+}
diff --git a/runsc/cmd/syscalls.go b/runsc/cmd/syscalls.go
new file mode 100644
index 000000000..9c8a66490
--- /dev/null
+++ b/runsc/cmd/syscalls.go
@@ -0,0 +1,347 @@
+// Copyright 2019 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package cmd
+
+import (
+	"context"
+	"encoding/csv"
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"sort"
+	"strconv"
+	"text/tabwriter"
+
+	"flag"
+	"github.com/google/subcommands"
+	"gvisor.googlesource.com/gvisor/pkg/sentry/kernel"
+)
+
+// Syscalls implements subcommands.Command for the "syscalls" command.
+type Syscalls struct {
+	output string
+	os     string
+	arch   string
+}
+
+// CompatibilityInfo is a map of system and architecture to compatibility doc.
+// Maps operating system to architecture to ArchInfo.
+type CompatibilityInfo map[string]map[string]ArchInfo
+
+// ArchInfo is compatbility doc for an architecture.
+type ArchInfo struct {
+	// Syscalls maps syscall number for the architecture to the doc.
+	Syscalls map[uintptr]SyscallDoc `json:"syscalls"`
+}
+
+// SyscallDoc represents a single item of syscall documentation.
+type SyscallDoc struct {
+	Name string `json:"name"`
+	num  uintptr
+
+	Support string   `json:"support"`
+	Note    string   `json:"note,omitempty"`
+	URLs    []string `json:"urls,omitempty"`
+}
+
+type outputFunc func(io.Writer, CompatibilityInfo) error
+
+var (
+	// The string name to use for printing compatibility for all OSes.
+	osAll = "all"
+
+	// The string name to use for printing compatibility for all architectures.
+	archAll = "all"
+
+	// A map of OS name to map of architecture name to syscall table.
+	syscallTableMap = make(map[string]map[string]*kernel.SyscallTable)
+
+	// A map of output type names to output functions.
+	outputMap = map[string]outputFunc{
+		"table": outputTable,
+		"json":  outputJSON,
+		"csv":   outputCSV,
+	}
+)
+
+// Name implements subcommands.Command.Name.
+func (*Syscalls) Name() string {
+	return "syscalls"
+}
+
+// Synopsis implements subcommands.Command.Synopsis.
+func (*Syscalls) Synopsis() string {
+	return "Print compatibility information for syscalls."
+}
+
+// Usage implements subcommands.Command.Usage.
+func (*Syscalls) Usage() string {
+	return `syscalls [options] - Print compatibility information for syscalls.
+`
+}
+
+// SetFlags implements subcommands.Command.SetFlags.
+func (s *Syscalls) SetFlags(f *flag.FlagSet) {
+	f.StringVar(&s.output, "o", "table", "Output format (table, csv, json).")
+	f.StringVar(&s.os, "os", osAll, "The OS (e.g. linux)")
+	f.StringVar(&s.arch, "arch", archAll, "The CPU architecture (e.g. amd64).")
+}
+
+// Execute implements subcommands.Command.Execute.
+func (s *Syscalls) Execute(_ context.Context, f *flag.FlagSet, args ...interface{}) subcommands.ExitStatus {
+	out, ok := outputMap[s.output]
+	if !ok {
+		Fatalf("Unsupported output format %q", s.output)
+	}
+
+	// Build map of all supported architectures.
+	tables := kernel.SyscallTables()
+	for _, t := range tables {
+		osMap, ok := syscallTableMap[t.OS.String()]
+		if !ok {
+			osMap = make(map[string]*kernel.SyscallTable)
+			syscallTableMap[t.OS.String()] = osMap
+		}
+		osMap[t.Arch.String()] = t
+	}
+
+	// Build a map of the architectures we want to output.
+	info, err := getCompatibilityInfo(s.os, s.arch)
+	if err != nil {
+		Fatalf("%v", err)
+	}
+
+	if err := out(os.Stdout, info); err != nil {
+		Fatalf("Error writing output: %v", err)
+	}
+
+	return subcommands.ExitSuccess
+}
+
+// getCompatibilityInfo returns compatibility info for the given OS name and
+// architecture name. Supports the special name 'all' for OS and architecture that
+// specifies that all supported OSes or architectures should be included.
+func getCompatibilityInfo(osName string, archName string) (CompatibilityInfo, error) {
+	info := CompatibilityInfo(make(map[string]map[string]ArchInfo))
+	if osName == osAll {
+		// Special processing for the 'all' OS name.
+		for osName, _ := range syscallTableMap {
+			info[osName] = make(map[string]ArchInfo)
+			// osName is a specific OS name.
+			if err := addToCompatibilityInfo(info, osName, archName); err != nil {
+				return info, err
+			}
+		}
+	} else {
+		// osName is a specific OS name.
+		info[osName] = make(map[string]ArchInfo)
+		if err := addToCompatibilityInfo(info, osName, archName); err != nil {
+			return info, err
+		}
+	}
+
+	return info, nil
+}
+
+// addToCompatibilityInfo adds ArchInfo for the given specific OS name and
+// architecture name. Supports the special architecture name 'all' to specify
+// that all supported architectures for the OS should be included.
+func addToCompatibilityInfo(info CompatibilityInfo, osName string, archName string) error {
+	if archName == archAll {
+		// Special processing for the 'all' architecture name.
+		for archName, _ := range syscallTableMap[osName] {
+			archInfo, err := getArchInfo(osName, archName)
+			if err != nil {
+				return err
+			}
+			info[osName][archName] = archInfo
+		}
+	} else {
+		// archName is a specific architecture name.
+		archInfo, err := getArchInfo(osName, archName)
+		if err != nil {
+			return err
+		}
+		info[osName][archName] = archInfo
+	}
+
+	return nil
+}
+
+// getArchInfo returns compatibility info for a specific OS and architecture.
+func getArchInfo(osName string, archName string) (ArchInfo, error) {
+	info := ArchInfo{}
+	info.Syscalls = make(map[uintptr]SyscallDoc)
+
+	t, ok := syscallTableMap[osName][archName]
+	if !ok {
+		return info, fmt.Errorf("syscall table for %s/%s not found", osName, archName)
+	}
+
+	for num, sc := range t.Table {
+		info.Syscalls[num] = SyscallDoc{
+			Name:    sc.Name,
+			num:     num,
+			Support: sc.SupportLevel.String(),
+			Note:    sc.Note,
+			URLs:    sc.URLs,
+		}
+	}
+
+	return info, nil
+}
+
+// outputTable outputs the syscall info in tabular format.
+func outputTable(w io.Writer, info CompatibilityInfo) error {
+	tw := tabwriter.NewWriter(w, 0, 0, 2, ' ', 0)
+
+	// Linux
+	for osName, osInfo := range info {
+		for archName, archInfo := range osInfo {
+			// Print the OS/arch
+			fmt.Fprintf(w, "%s/%s:\n\n", osName, archName)
+
+			// Sort the syscalls for output in the table.
+			sortedCalls := []SyscallDoc{}
+			for _, sc := range archInfo.Syscalls {
+				sortedCalls = append(sortedCalls, sc)
+			}
+			sort.Slice(sortedCalls, func(i, j int) bool {
+				return sortedCalls[i].num < sortedCalls[j].num
+			})
+
+			// Write the header
+			_, err := fmt.Fprintf(tw, "%s\t%s\t%s\t%s\n",
+				"NUM",
+				"NAME",
+				"SUPPORT",
+				"NOTE",
+			)
+			if err != nil {
+				return err
+			}
+
+			// Write each syscall entry
+			for _, sc := range sortedCalls {
+				_, err = fmt.Fprintf(tw, "%s\t%s\t%s\t%s\n",
+					strconv.FormatInt(int64(sc.num), 10),
+					sc.Name,
+					sc.Support,
+					sc.Note,
+				)
+				if err != nil {
+					return err
+				}
+				// Add issue urls to note.
+				for _, url := range sc.URLs {
+					_, err = fmt.Fprintf(tw, "%s\t%s\t%s\tSee: %s\t\n",
+						"",
+						"",
+						"",
+						url,
+					)
+					if err != nil {
+						return err
+					}
+				}
+			}
+
+			err = tw.Flush()
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+// outputJSON outputs the syscall info in JSON format.
+func outputJSON(w io.Writer, info CompatibilityInfo) error {
+	e := json.NewEncoder(w)
+	e.SetIndent("", "  ")
+	return e.Encode(info)
+}
+
+// numberedRow is aCSV row annotated by syscall number (used for sorting)
+type numberedRow struct {
+	num uintptr
+	row []string
+}
+
+// outputCSV outputs the syscall info in tabular format.
+func outputCSV(w io.Writer, info CompatibilityInfo) error {
+	csvWriter := csv.NewWriter(w)
+
+	// Linux
+	for osName, osInfo := range info {
+		for archName, archInfo := range osInfo {
+			// Sort the syscalls for output in the table.
+			sortedCalls := []numberedRow{}
+			for _, sc := range archInfo.Syscalls {
+				// Add issue urls to note.
+				note := sc.Note
+				for _, url := range sc.URLs {
+					note = fmt.Sprintf("%s\nSee: %s", note, url)
+				}
+
+				sortedCalls = append(sortedCalls, numberedRow{
+					num: sc.num,
+					row: []string{
+						osName,
+						archName,
+						strconv.FormatInt(int64(sc.num), 10),
+						sc.Name,
+						sc.Support,
+						note,
+					},
+				})
+			}
+			sort.Slice(sortedCalls, func(i, j int) bool {
+				return sortedCalls[i].num < sortedCalls[j].num
+			})
+
+			// Write the header
+			err := csvWriter.Write([]string{
+				"OS",
+				"Arch",
+				"Num",
+				"Name",
+				"Support",
+				"Note",
+			})
+			if err != nil {
+				return err
+			}
+
+			// Write each syscall entry
+			for _, sc := range sortedCalls {
+				err = csvWriter.Write(sc.row)
+				if err != nil {
+					return err
+				}
+			}
+
+			csvWriter.Flush()
+			err = csvWriter.Error()
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
diff --git a/runsc/main.go b/runsc/main.go
index 6f8e6e378..a214f6ba0 100644
--- a/runsc/main.go
+++ b/runsc/main.go
@@ -76,7 +76,9 @@ var (
 
 func main() {
 	// Help and flags commands are generated automatically.
-	subcommands.Register(subcommands.HelpCommand(), "")
+	help := cmd.NewHelp(subcommands.DefaultCommander)
+	help.Register(new(cmd.Syscalls))
+	subcommands.Register(help, "")
 	subcommands.Register(subcommands.FlagsCommand(), "")
 
 	// Register user-facing runsc commands.