container: use /proc/self/exe directly

This is a more reliable form of pathname to self and also cheaper than os.Executable.

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

cmd/sharefs/fuse.go

@@ -33,6 +33,7 @@ import (
 
 	"hakurei.app/container"
 	"hakurei.app/container/check"
+	"hakurei.app/container/fhs"
 	"hakurei.app/container/std"
 	"hakurei.app/hst"
 	"hakurei.app/internal/helper/proc"
@@ -441,12 +442,7 @@ func _main(s ...string) (exitCode int) {
 		// keep fuse_parse_cmdline happy in the container
 		z.Tmpfs(check.MustAbs(container.Nonexistent), 1<<10, 0755)
 
-		if a, err := check.NewAbs(container.MustExecutable(msg)); err != nil {
-			log.Println(err)
-			return 5
-		} else {
-			z.Path = a
-		}
+		z.Path = fhs.AbsProcSelfExe
 		z.Args = s
 		z.ForwardCancel = true
 		z.SeccompPresets |= std.PresetStrict

container/container.go

@@ -525,7 +525,7 @@ func New(ctx context.Context, msg message.Msg) *Container {
 	p := &Container{ctx: ctx, msg: msg, Params: Params{Ops: new(Ops)}}
 	c, cancel := context.WithCancel(ctx)
 	p.cancel = cancel
-	p.cmd = exec.CommandContext(c, MustExecutable(msg))
+	p.cmd = exec.CommandContext(c, fhs.ProcSelfExe)
 	return p
 }
 

container/container_test.go

@@ -773,14 +773,13 @@ func TestMain(m *testing.M) {
 func helperNewContainerLibPaths(ctx context.Context, libPaths *[]*check.Absolute, args ...string) (c *container.Container) {
 	msg := message.New(nil)
 	msg.SwapVerbose(testing.Verbose())
-	executable := check.MustAbs(container.MustExecutable(msg))
 
 	c = container.NewCommand(ctx, msg, absHelperInnerPath, "helper", args...)
 	c.Env = append(c.Env, envDoCheck+"=1")
-	c.Bind(executable, absHelperInnerPath, 0)
+	c.Bind(fhs.AbsProcSelfExe, absHelperInnerPath, 0)
 
 	// in case test has cgo enabled
-	if entries, err := ldd.Resolve(ctx, msg, executable); err != nil {
+	if entries, err := ldd.Resolve(ctx, msg, nil); err != nil {
 		log.Fatalf("ldd: %v", err)
 	} else {
 		*libPaths = ldd.Path(entries)

container/executable.go

@@ -28,6 +28,9 @@ func copyExecutable(msg message.Msg) {
 	}
 }
 
+// MustExecutable calls [os.Executable] and terminates the process on error.
+//
+// Deprecated: This is no longer used and will be removed in 0.4.
 func MustExecutable(msg message.Msg) string {
 	executableOnce.Do(func() { copyExecutable(msg) })
 	return executable

container/fhs/abs.go

@@ -42,6 +42,8 @@ var (
 	AbsDevShm = unsafeAbs(DevShm)
 	// AbsProc is [Proc] as [check.Absolute].
 	AbsProc = unsafeAbs(Proc)
+	// AbsProcSelfExe is [ProcSelfExe] as [check.Absolute].
+	AbsProcSelfExe = unsafeAbs(ProcSelfExe)
 	// AbsSys is [Sys] as [check.Absolute].
 	AbsSys = unsafeAbs(Sys)
 )

container/fhs/fhs.go

@@ -41,6 +41,10 @@ const (
 	// ProcSys points to a hierarchy below /proc/ that exposes a number of
 	// kernel tunables.
 	ProcSys = Proc + "sys/"
+	// ProcSelf resolves to the process's own /proc/pid directory.
+	ProcSelf = Proc + "self/"
+	// ProcSelfExe is a symbolic link to program pathname.
+	ProcSelfExe = ProcSelf + "exe"
 	// Sys points to a virtual kernel file system exposing discovered devices
 	// and other functionality.
 	Sys = "/sys/"

internal/lockedfile/internal/filelock/filelock_test.go

@@ -14,7 +14,7 @@ import (
 	"testing"
 	"time"
 
-	"hakurei.app/container"
+	"hakurei.app/container/fhs"
 	"hakurei.app/internal/lockedfile/internal/filelock"
 	"hakurei.app/internal/lockedfile/internal/testexec"
 )
@@ -197,7 +197,7 @@ func TestLockNotDroppedByExecCommand(t *testing.T) {
 	// Some kinds of file locks are dropped when a duplicated or forked file
 	// descriptor is unlocked. Double-check that the approach used by os/exec does
 	// not accidentally drop locks.
-	cmd := testexec.CommandContext(t, t.Context(), container.MustExecutable(nil), "-test.run=^$")
+	cmd := testexec.CommandContext(t, t.Context(), fhs.ProcSelfExe, "-test.run=^$")
 	if err := cmd.Run(); err != nil {
 		t.Fatalf("exec failed: %v", err)
 	}

internal/lockedfile/lockedfile_test.go

@@ -15,7 +15,7 @@ import (
 	"testing"
 	"time"
 
-	"hakurei.app/container"
+	"hakurei.app/container/fhs"
 	"hakurei.app/internal/lockedfile"
 	"hakurei.app/internal/lockedfile/internal/testexec"
 )
@@ -215,7 +215,7 @@ func TestSpuriousEDEADLK(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	cmd := testexec.CommandContext(t, t.Context(), container.MustExecutable(nil), "-test.run=^"+t.Name()+"$")
+	cmd := testexec.CommandContext(t, t.Context(), fhs.ProcSelfExe, "-test.run=^"+t.Name()+"$")
 	cmd.Env = append(os.Environ(), fmt.Sprintf("%s=%s", dirVar, dir))
 
 	qDone := make(chan struct{})