sandbox/seccomp: implement syscall lookup

This uses the Go map and is verified against libseccomp.

Signed-off-by: Ophestra <cat@gensokyo.uk>

flake.nix

@@ -187,12 +187,14 @@
 
           generateSyscallTable = pkgs.mkShell {
             # this should be made cross-platform via nix
-            shellHook = ''
-              exec ${pkgs.perl}/bin/perl \
+            shellHook = "exec ${pkgs.writeShellScript "generate-syscall-table" ''
+              set -e
+              ${pkgs.perl}/bin/perl \
                 sandbox/seccomp/mksysnum_linux.pl \
-                ${pkgs.linuxHeaders}/include/asm/unistd_64.h > \
+                ${pkgs.linuxHeaders}/include/asm/unistd_64.h | \
+                ${pkgs.go}/bin/gofmt > \
                 sandbox/seccomp/syscall_linux_amd64.go
-            '';
+            ''}";
           };
         }
       );

sandbox/seccomp/syscall.go

@@ -0,0 +1,28 @@
+package seccomp
+
+import "iter"
+
+// Syscalls returns an iterator over all wired syscalls.
+func Syscalls() iter.Seq2[string, int] {
+	return func(yield func(string, int) bool) {
+		for name, num := range syscallNum {
+			if !yield(name, num) {
+				return
+			}
+		}
+		for name, num := range syscallNumExtra {
+			if !yield(name, num) {
+				return
+			}
+		}
+	}
+}
+
+// SyscallResolveName resolves a syscall number from its string representation.
+func SyscallResolveName(name string) (num int, ok bool) {
+	if num, ok = syscallNum[name]; ok {
+		return
+	}
+	num, ok = syscallNumExtra[name]
+	return
+}

sandbox/seccomp/syscall_test.go

@@ -5,12 +5,16 @@ import (
 )
 
 func TestSyscallResolveName(t *testing.T) {
-	for name, want := range syscallNum {
+	for name, want := range Syscalls() {
 		t.Run(name, func(t *testing.T) {
 			if got := syscallResolveName(name); got != want {
 				t.Errorf("syscallResolveName(%q) = %d, want %d",
 					name, got, want)
 			}
+			if got, ok := SyscallResolveName(name); !ok || got != want {
+				t.Errorf("SyscallResolveName(%q) = %d, want %d",
+					name, got, want)
+			}
 		})
 	}
 }