sys::ptrace: adding ::syscall_info() for linux/glibc. (#2627)

to retrieve the very system call which stopped the process.
Can be found the type of calls and their related informations.
e.g. on exit we get the return value of the call.

Author: devnexen

changelog/2627.added.md

@@ -0,0 +1 @@
+Add `ptrace::syscall_info` for linux/glibc

src/sys/ptrace/linux.rs

@@ -146,6 +146,8 @@ libc_enum! {
         #[cfg(all(target_os = "linux", target_env = "gnu",
                   any(target_arch = "x86", target_arch = "x86_64")))]
         PTRACE_SYSEMU_SINGLESTEP,
+        #[cfg(all(target_os = "linux", target_env = "gnu"))]
+        PTRACE_GET_SYSCALL_INFO,
     }
 }
 
@@ -567,6 +569,13 @@ pub fn setsiginfo(pid: Pid, sig: &siginfo_t) -> Result<()> {
     }
 }
 
+/// Get the informations of the syscall that caused the stop, as with
+/// `ptrace(PTRACE_GET_SYSCALL_INFO, ...`.
+#[cfg(all(target_os = "linux", target_env = "gnu"))]
+pub fn syscall_info(pid: Pid) -> Result<libc::ptrace_syscall_info> {
+    ptrace_get_data::<libc::ptrace_syscall_info>(Request::PTRACE_GET_SYSCALL_INFO, pid)
+}
+
 /// Sets the process as traceable, as with `ptrace(PTRACE_TRACEME, ...)`
 ///
 /// Indicates that this process is to be traced by its parent.

test/sys/test_ptrace.rs

@@ -381,3 +381,32 @@ fn test_ptrace_regsets() {
         }
     }
 }
+
+#[cfg(all(target_os = "linux", target_env = "gnu"))]
+#[test]
+fn test_ptrace_syscall_info() {
+    use nix::sys::ptrace;
+    use nix::sys::wait::{waitpid, WaitStatus};
+    use nix::unistd::fork;
+    use nix::unistd::ForkResult::*;
+
+    require_capability!("test_ptrace_syscall_info", CAP_SYS_PTRACE);
+
+    let _m = crate::FORK_MTX.lock();
+    match unsafe { fork() }.expect("Error: Fork Failed") {
+        Child => {
+            ptrace::traceme().unwrap();
+            std::thread::sleep(std::time::Duration::from_millis(1000));
+            unsafe {
+                ::libc::_exit(0);
+            }
+        }
+        Parent { child } => loop {
+            if let Ok(WaitStatus::Exited(_, 0)) = waitpid(child, None) {
+                break;
+            }
+            let si = ptrace::syscall_info(child).unwrap();
+            assert!(si.op >= libc::PTRACE_SYSCALL_INFO_ENTRY);
+        },
+    }
+}