seccomp: Lazily construct precompiled seccomp programs

pkg/seccomp/precompiledseccomp/precompile_gen.go

@@ -39,8 +39,8 @@ const (
 	packageNameStandin            = "precompiled"
 	precompiledseccompPackageName = "precompiledseccomp"
 	registrationComment           = "PROGRAM_REGISTRATION_GOES_HERE_THIS_IS_A_LOAD_BEARING_COMMENT"
+	namesListComment              = "PROGRAM_NAMES_LIST_GOES_HERE_THIS_IS_A_LOAD_BEARING_COMMENT"
 	disabledAtBuildtimeComment    = "PRECOMPILATION_DISABLED_AT_BUILD_TIME_THIS_IS_A_LOAD_BEARING_COMMENT"
-	programsMapVarName            = "programs"
 )
 
 // Flags.
@@ -105,16 +105,12 @@ func main() {
 			}
 			processedPackageComment = true
 		case strings.Contains(line, registrationComment):
-			var indent string
-			for {
-				var found bool
-				if line, found = strings.CutPrefix(line, "\t"); !found {
-					break
-				}
-				indent += "\t"
+			for _, program := range programs {
+				fmt.Fprint(outFile, program.SwitchCase(precompiledseccompPackageName))
 			}
+		case strings.Contains(line, namesListComment):
 			for _, program := range programs {
-				fmt.Fprint(outFile, program.Registration(indent, precompiledseccompPackageName, programsMapVarName))
+				fmt.Fprintf(outFile, "\t%q,\n", program.Name)
 			}
 		case strings.Contains(line, disabledAtBuildtimeComment):
 			fmt.Fprintf(outFile, "const PrecompilationDisabledAtBuildTime = %t\n", disabledAtBuildTime)

pkg/seccomp/precompiledseccomp/precompiled_lib.tmpl.go

@@ -17,20 +17,15 @@
 package precompiled
 
 import (
-	"sort"
-
 	"gvisor.dev/gvisor/pkg/seccomp/precompiledseccomp"
-	"gvisor.dev/gvisor/pkg/sync"
 )
 
 var (
-	// precompiledPrograms holds registered programs.
-	// It is populated in `registerPrograms`.
-	precompiledPrograms map[string]precompiledseccomp.Program = nil
-
-	// registerPrecompiledProgramsOnce ensures that program registration
-	// happens only once.
-	registerPrecompiledProgramsOnce sync.Once
+	// precompiledProgramNames is the sorted list of all precompiled program
+	// names. It is populated at generation time and used by `ListPrecompiled`.
+	precompiledProgramNames = []string{
+		// PROGRAM_NAMES_LIST_GOES_HERE_THIS_IS_A_LOAD_BEARING_COMMENT
+	}
 )
 
 // PrecompilationDisabledAtBuildTime is a constant that is used to
@@ -40,25 +35,13 @@ const PrecompilationDisabledAtBuildTime = false // PRECOMPILATION_DISABLED_AT_BU
 // GetPrecompiled returns the precompiled program for the given name,
 // and whether that program name exists.
 func GetPrecompiled(programName string) (precompiledseccomp.Program, bool) {
-	registerPrecompiledProgramsOnce.Do(registerPrograms)
-	program, ok := precompiledPrograms[programName]
-	return program, ok
+	switch programName {
+	// PROGRAM_REGISTRATION_GOES_HERE_THIS_IS_A_LOAD_BEARING_COMMENT
+	}
+	return precompiledseccomp.Program{}, false
 }
 
 // ListPrecompiled returns a list of all registered program names.
 func ListPrecompiled() []string {
-	registerPrecompiledProgramsOnce.Do(registerPrograms)
-	programNames := make([]string, 0, len(precompiledPrograms))
-	for name := range precompiledPrograms {
-		programNames = append(programNames, name)
-	}
-	sort.Strings(programNames)
-	return programNames
-}
-
-// registerPrograms registers available programs inside `precompiledPrograms`.
-func registerPrograms() {
-	programs := make(map[string]precompiledseccomp.Program)
-	// PROGRAM_REGISTRATION_GOES_HERE_THIS_IS_A_LOAD_BEARING_COMMENT
-	precompiledPrograms = programs
+	return append([]string(nil), precompiledProgramNames...)
 }

pkg/seccomp/precompiledseccomp/precompiledseccomp.go

@@ -360,10 +360,9 @@ func uint32SliceToInstructions(bytecode32 []uint32) ([]bpf.Instruction, error) {
 	return bpf.ParseBytecode(bytecode)
 }
 
-// Registration outputs Go code that registers this programs in a
-// `map[string]Program` variable named `programsMapVarName` which maps
-// programs names to their `Program` struct.
-// It is used when embedding precompiled programs into a Go library file.
-func (program Program) Registration(indentPrefix, pkgName, programsMapVarName string) string {
-	return fmt.Sprintf("%s%s[%q] = %s\n", indentPrefix, programsMapVarName, program.Name, program.Expr(indentPrefix, pkgName))
+func (program Program) SwitchCase(pkgName string) string {
+	var sb strings.Builder
+	fmt.Fprintf(&sb, "\tcase %q:\n", program.Name)
+	fmt.Fprintf(&sb, "\t\treturn %s, true\n", program.Expr("\t\t\t", pkgName))
+	return sb.String()
 }