ripple/minitrace: log openat paths

Co-authored-by: V <v@unfathomable.blue>
Change-Id: Idcb3c29c4761158be788511f5f4bdb3003edf909

1 files changed, 37 insertions, 5 deletions

diff --git a/ripple/minitrace/src/main.rs b/ripple/minitrace/src/main.rs
index 5fa35da..6b7c044 100644
--- a/ripple/minitrace/src/main.rs
+++ b/ripple/minitrace/src/main.rs
@@ -14,7 +14,15 @@ use {
 		},
 		unistd::Pid,
 	},
-	std::{convert::TryInto, env, os::unix::process::CommandExt, process::Command},
+	std::{
+		convert::TryInto,
+		env,
+		ffi::CString,
+		fs::File,
+		io::{self, BufRead, Seek, SeekFrom},
+		os::unix::process::CommandExt,
+		process::Command,
+	},
 };
 
 // TODO(edef): consider implementing this in terms of TID?
@@ -40,6 +48,7 @@ impl Tid {
 #[derive(Debug)]
 struct Process {
 	tgid: Tgid,
+	mem: File,
 }
 
 impl Process {
@@ -66,7 +75,25 @@ impl Process {
 			status => bail!("unexpected child state: {:?}", status),
 		}
 
-		Ok(Process { tgid })
+		Ok(Process {
+			tgid,
+			mem: File::open(format!("/proc/{}/mem", tgid.0))
+				.context("Couldn't open child memory")?,
+		})
+	}
+
+	fn read_mem_cstr(&self, ptr: u64) -> Result<CString> {
+		let mut mem = io::BufReader::new(&self.mem);
+		mem.seek(SeekFrom::Start(ptr))?;
+		let mut buf = vec![];
+		mem.read_until(0, &mut buf)?;
+
+		// TODO(V): replace with CString::from_vec_with_nul when we update to Rust 1.58
+		if buf.pop() != Some(0) {
+			bail!("Couldn't find null terminator");
+		}
+
+		Ok(CString::new(buf).expect("logic error"))
 	}
 }
 
@@ -139,7 +166,7 @@ fn main() -> Result<()> {
 
 				syscall_state = Some(EntryExit::Entry(entry));
 
-				if !check_syscall(entry) {
+				if !check_syscall(&process, entry) {
 					ptrace::kill(event_tid.as_pid())?;
 					panic!("unsupported syscall {:?}", entry);
 				}
@@ -169,7 +196,7 @@ fn main() -> Result<()> {
 	Ok(())
 }
 
-fn check_syscall(entry: SyscallEntry) -> bool {
+fn check_syscall(process: &Process, entry: SyscallEntry) -> bool {
 	match entry.number {
 		// read
 		0 => {}
@@ -236,12 +263,17 @@ fn check_syscall(entry: SyscallEntry) -> bool {
 
 		// openat
 		257 => {
-			let [dirfd, _pathname, _flags, _mode, _, _] = entry.args;
+			let [dirfd, pathname, _flags, _mode, _, _] = entry.args;
 			const AT_FDCWD: i32 = -100;
 
 			if dirfd.try_into() == Ok(AT_FDCWD) {
 				return false;
 			}
+
+			println!(
+				"openat(AT_FDCWD, {:?}, ..)",
+				process.read_mem_cstr(pathname).unwrap()
+			);
 		}
 
 		// newfstatat