Extend -Y option to decode PIDs in arguments and return values

This change extends -Y/--decode-pids=comm option.  In addition to the
information printed before this change, command names would be printed
also for PIDs appeared in syscall arguments and return values.

For example:

  getppid()                  = 3781395<strace>
  getpid()                   = 3781398<a.out>
  pidfd_open(1<systemd>, 0)  = 3<pid:1<systemd>>

NOTE: The code printing the pid in printclockname() is not changed in
this commit.  CLOCKID_TO_FD macro used in printclockname() was removed
from the kernel, so printclockname() may change drastically in the
near future.

* src/defs.h (maybe_printpid_comm): New function declaration.
* src/strace.c (maybe_printpid_comm): New function printing
command name for the given PID.
* src/pidns.c (printpid_translation): Call `maybe_printpid_comm'.
* tests/strace--decode-pids-comm.c (do_default_action): Update expected
output.

Signed-off-by: Masatake YAMATO <yamato@redhat.com>
Co-authored-by: Dmitry V. Levin <ldv@strace.io>

4 files changed, 35 insertions, 12 deletions

diff --git a/src/defs.h b/src/defs.h
index 49636b967..936609ae2 100644
--- a/src/defs.h
+++ b/src/defs.h
@@ -1492,6 +1492,8 @@ extern void kvm_vcpu_info_free(struct tcb *);
 # endif
 
 extern void maybe_load_task_comm(struct tcb *tcp);
+/* Print the contents of /proc/$pid/comm. */
+extern void maybe_printpid_comm(int pid);
 
 static inline int
 printstrn(struct tcb *tcp, kernel_ulong_t addr, kernel_ulong_t len)
diff --git a/src/pidns.c b/src/pidns.c
index eda87aad9..9b8504f7c 100644
--- a/src/pidns.c
+++ b/src/pidns.c
@@ -527,12 +527,18 @@ get_proc_pid(int pid)
 static void
 printpid_translation(struct tcb *tcp, int pid, enum pid_type type)
 {
-	if (!(pid_decoding & PID_DECODING_NS_TRANSLATION))
-		return;
-
-	int strace_pid = translate_pid(tcp, pid, type, NULL);
-	if (strace_pid && strace_pid != pid)
-		tprintf_comment("%d in strace's PID NS", strace_pid);
+	if ((pid_decoding & (PID_DECODING_COMM|PID_DECODING_NS_TRANSLATION))) {
+		int strace_pid = translate_pid(tcp, pid, type, NULL);
+		if (strace_pid) {
+			if ((pid_decoding & PID_DECODING_COMM) &&
+			    (type == PT_TID || type == PT_TGID))
+				maybe_printpid_comm(strace_pid);
+			if ((pid_decoding & PID_DECODING_NS_TRANSLATION) &&
+			    strace_pid != pid)
+				tprintf_comment("%d in strace's PID NS",
+						strace_pid);
+		}
+	}
 }
 
 void
diff --git a/src/strace.c b/src/strace.c
index 950644040..38165a1a3 100644
--- a/src/strace.c
+++ b/src/strace.c
@@ -948,6 +948,19 @@ load_pid_comm(int pid, char *buf, size_t buf_size)
 }
 
 void
+maybe_printpid_comm(int pid)
+{
+	if (!(pid_decoding & PID_DECODING_COMM))
+		return;
+
+	char buf[PROC_COMM_LEN];
+	load_pid_comm(pid, buf, sizeof(buf));
+	tprints("<");
+	tprints(buf);
+	tprints(">");
+}
+
+void
 maybe_load_task_comm(struct tcb *tcp)
 {
 	if (!(pid_decoding & PID_DECODING_COMM))
diff --git a/tests/strace--decode-pids-comm.c b/tests/strace--decode-pids-comm.c
index eca990c1c..d5767853f 100644
--- a/tests/strace--decode-pids-comm.c
+++ b/tests/strace--decode-pids-comm.c
@@ -39,11 +39,13 @@ do_default_action(void)
 	char comm[sizeof(NEW_NAME)];
 	if (prctl(PR_GET_NAME, comm))
 		perror_msg_and_skip("PR_GET_NAME");
+	char ocomm[sizeof(comm)];
+	strcpy(ocomm, comm);
 
 	pid_t pid  = getpid();
 	pid_t ppid = getppid();
 
-	printf("%-5d<%s> getppid() = %d\n", pid, comm, ppid);
+	printf("%-5d<%s> getppid() = %d<%s>\n", pid, comm, ppid, "strace");
 	fflush(stdout);
 
 	pid_t child = fork();
@@ -52,18 +54,18 @@ do_default_action(void)
 	else if (child == 0) {
 		pid = getpid();
 		ppid = getppid();
-		printf("%-5d<%s> getppid() = %d\n", pid, comm, ppid);
+		printf("%-5d<%s> getppid() = %d<%s>\n", pid, comm, ppid, ocomm);
 
 		strcpy(comm, NEW_NAME);
 		prctl(PR_SET_NAME, comm);
 		prctl(PR_GET_NAME, comm);
 
 		ppid = getppid();
-		printf("%-5d<%s> getppid() = %d\n", pid, comm, ppid);
+		printf("%-5d<%s> getppid() = %d<%s>\n", pid, comm, ppid, ocomm);
 
 		long rc = syscall(__NR_tgkill, ppid, ppid, SIGCONT);
-		printf("%-5d<%s> tgkill(%d, %d, SIGCONT) = %s\n",
-		       pid, comm, ppid, ppid, sprintrc(rc));
+		printf("%-5d<%s> tgkill(%d<%s>, %d<%s>, SIGCONT) = %s\n",
+		       pid, comm, ppid, ocomm, ppid, ocomm, sprintrc(rc));
 
 		fflush(stdout);
 		char *args[] = { (char *) "unused", (char *) "execve", NULL };
@@ -79,7 +81,7 @@ do_default_action(void)
 		printf("%-5d<exe> +++ exited with 0 +++\n", child);
 
 		ppid = getppid();
-		printf("%-5d<%s> getppid() = %d\n", pid, comm, ppid);
+		printf("%-5d<%s> getppid() = %d<%s>\n", pid, comm, ppid, "strace");
 		printf("%-5d<%s> +++ exited with 0 +++\n", pid, comm);
 		return WEXITSTATUS(status);
 	}