handle ESRCH in more ptrace callsites (#91)

we are seeing processes exit with the following:

```
run process: run_parent03:44
Caused by:03:44
    0: handle_syscall pid=11203:44
    1: get_target_path03:44
    2: ptrace::getregs03:44
    3: ESRCH: No such process
```

a traced process can exit at any time so any ptrace calls that operate
on the pid must check esrch to see if the traced process has exited and
handle it appropriately

we already do it in a bunch of places but do it in more

Author: jackyzha0

npm/darwin-arm64/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@replit/ruspty-darwin-arm64",
-  "version": "3.5.2",
+  "version": "3.5.3",
   "os": [
     "darwin"
   ],

npm/darwin-x64/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@replit/ruspty-darwin-x64",
-  "version": "3.5.2",
+  "version": "3.5.3",
   "os": [
     "darwin"
   ],

npm/linux-x64-gnu/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@replit/ruspty-linux-x64-gnu",
-  "version": "3.5.2",
+  "version": "3.5.3",
   "os": [
     "linux"
   ],

package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "@replit/ruspty",
-  "version": "3.5.2",
+  "version": "3.5.3",
   "main": "dist/wrapper.js",
   "types": "dist/wrapper.d.ts",
   "author": "Szymon Kaliski <hi@szymonkaliski.com>",

package.json

@@ -86,7 +86,11 @@ struct SyscallTarget {
 
 /// Get the tracee's target path for the syscall that is about to be executed by the kernel.
 fn get_syscall_targets(pid: Pid) -> Result<Vec<SyscallTarget>> {
-  let regs = ptrace::getregs(pid).context("ptrace::getregs")?;
+  let regs = match ptrace::getregs(pid) {
+    Ok(regs) => regs,
+    Err(Error::ESRCH) => return Ok(vec![]), // process gone, no targets
+    Err(err) => return Err(err).context("ptrace::getregs"),
+  };
   if regs.rax != (-(Error::ENOSYS as i32)) as u64 {
     // This is a syscall-exit-stop, and we have already made the decision of allowing / denying the operation.
     return Ok(vec![]);
@@ -483,7 +487,16 @@ fn run_parent(main_pid: Pid, options: &Options) -> Result<i32> {
       return Err(err).context("ptrace::setoptions");
     }
   }
-  ptrace::syscall(main_pid, None).context("Failed continue process")?;
+  match ptrace::syscall(main_pid, None) {
+    Ok(_) => {}
+    Err(Error::ESRCH) => {
+      // The child process has already exited.
+      return Ok(0);
+    }
+    Err(err) => {
+      return Err(err).context("failed to continue process");
+    }
+  }
 
   loop {
     match wait() {
@@ -514,16 +527,21 @@ fn run_parent(main_pid: Pid, options: &Options) -> Result<i32> {
         }
         signum @ Signal::SIGSTOP => {
           debug!(signal:?=signum, pid:? = pid; "signal");
-          ptrace::setoptions(
+          match ptrace::setoptions(
             pid,
             ptrace::Options::PTRACE_O_TRACESYSGOOD
               | ptrace::Options::PTRACE_O_TRACEFORK
               | ptrace::Options::PTRACE_O_TRACEVFORK
               | ptrace::Options::PTRACE_O_TRACECLONE
               | ptrace::Options::PTRACE_O_EXITKILL
               | ptrace::Options::PTRACE_O_TRACEEXIT,
-          )
-          .context("setoptions")?;
+          ) {
+            Ok(_) => {}
+            Err(Error::ESRCH) => {}
+            Err(err) => {
+              return Err(anyhow::Error::new(err).context("setoptions"));
+            }
+          }
           match ptrace::syscall(pid, None) {
             Ok(_) => {}
             Err(Error::ESRCH) => {}