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

2 files changed, 59 insertions, 9 deletions

diff --git a/pkg/sentry/kernel/syscalls.go b/pkg/sentry/kernel/syscalls.go
index 0572053db..27cd3728b 100644
--- a/pkg/sentry/kernel/syscalls.go
+++ b/pkg/sentry/kernel/syscalls.go
@@ -32,6 +32,51 @@ import (
 // syscall.
 const maxSyscallNum = 2000
 
+// SyscallSupportLevel is a syscall support levels.
+type SyscallSupportLevel int
+
+// String returns a human readable represetation of the support level.
+func (l SyscallSupportLevel) String() string {
+	switch l {
+	case SupportUnimplemented:
+		return "Unimplemented"
+	case SupportPartial:
+		return "Partial Support"
+	case SupportFull:
+		return "Full Support"
+	default:
+		return "Undocumented"
+	}
+}
+
+const (
+	// SupportUndocumented indicates the syscall is not documented yet.
+	SupportUndocumented = iota
+
+	// SupportUnimplemented indicates the syscall is unimplemented.
+	SupportUnimplemented
+
+	// SupportPartial indicates the syscall is partially supported.
+	SupportPartial
+
+	// SupportFull indicates the syscall is fully supported.
+	SupportFull
+)
+
+// Syscall includes the syscall implementation and compatibility information.
+type Syscall struct {
+	// Name is the syscall name.
+	Name string
+	// Fn is the implementation of the syscall.
+	Fn SyscallFn
+	// SupportLevel is the level of support implemented in gVisor.
+	SupportLevel SyscallSupportLevel
+	// Note describes the compatibility of the syscall.
+	Note string
+	// URLs is set of URLs to any relevant bugs or issues.
+	URLs []string
+}
+
 // SyscallFn is a syscall implementation.
 type SyscallFn func(t *Task, args arch.SyscallArguments) (uintptr, *SyscallControl, error)
 
@@ -83,7 +128,7 @@ type SyscallFlagsTable struct {
 // Init initializes the struct, with all syscalls in table set to enable.
 //
 // max is the largest syscall number in table.
-func (e *SyscallFlagsTable) init(table map[uintptr]SyscallFn, max uintptr) {
+func (e *SyscallFlagsTable) init(table map[uintptr]Syscall, max uintptr) {
 	e.enable = make([]uint32, max+1)
 	for num := range table {
 		e.enable[num] = syscallPresent
@@ -194,7 +239,7 @@ type SyscallTable struct {
 	AuditNumber uint32 `state:"manual"`
 
 	// Table is the collection of functions.
-	Table map[uintptr]SyscallFn `state:"manual"`
+	Table map[uintptr]Syscall `state:"manual"`
 
 	// lookup is a fixed-size array that holds the syscalls (indexed by
 	// their numbers). It is used for fast look ups.
@@ -247,7 +292,7 @@ func LookupSyscallTable(os abi.OS, a arch.Arch) (*SyscallTable, bool) {
 func RegisterSyscallTable(s *SyscallTable) {
 	if s.Table == nil {
 		// Ensure non-nil lookup table.
-		s.Table = make(map[uintptr]SyscallFn)
+		s.Table = make(map[uintptr]Syscall)
 	}
 	if s.Emulate == nil {
 		// Ensure non-nil emulate table.
@@ -268,8 +313,8 @@ func RegisterSyscallTable(s *SyscallTable) {
 	s.lookup = make([]SyscallFn, max+1)
 
 	// Initialize the fast-lookup table.
-	for num, fn := range s.Table {
-		s.lookup[num] = fn
+	for num, sc := range s.Table {
+		s.lookup[num] = sc.Fn
 	}
 
 	s.FeatureEnable.init(s.Table, max)
@@ -303,5 +348,8 @@ func (s *SyscallTable) LookupEmulate(addr usermem.Addr) (uintptr, bool) {
 // mapLookup is similar to Lookup, except that it only uses the syscall table,
 // that is, it skips the fast look array. This is available for benchmarking.
 func (s *SyscallTable) mapLookup(sysno uintptr) SyscallFn {
-	return s.Table[sysno]
+	if sc, ok := s.Table[sysno]; ok {
+		return sc.Fn
+	}
+	return nil
 }
diff --git a/pkg/sentry/kernel/table_test.go b/pkg/sentry/kernel/table_test.go
index 8f7cdb9f3..3f2b042c8 100644
--- a/pkg/sentry/kernel/table_test.go
+++ b/pkg/sentry/kernel/table_test.go
@@ -26,11 +26,13 @@ const (
 )
 
 func createSyscallTable() *SyscallTable {
-	m := make(map[uintptr]SyscallFn)
+	m := make(map[uintptr]Syscall)
 	for i := uintptr(0); i <= maxTestSyscall; i++ {
 		j := i
-		m[i] = func(*Task, arch.SyscallArguments) (uintptr, *SyscallControl, error) {
-			return j, nil, nil
+		m[i] = Syscall{
+			Fn: func(*Task, arch.SyscallArguments) (uintptr, *SyscallControl, error) {
+				return j, nil, nil
+			},
 		}
 	}