From ee913da0363be4ee94451a9894f2f54a5e69d5e5 Mon Sep 17 00:00:00 2001
From: mar77i <mar77i@protonmail.ch>
Date: Mon, 23 Mar 2026 22:09:59 +0100
Subject: [PATCH] apply timer after parsing args. add help message

---
 parse_args.c | 30 +++++++++++++++++++++++++++++-
 perftrace.c  |  6 +++---
 2 files changed, 32 insertions(+), 4 deletions(-)

diff --git a/parse_args.c b/parse_args.c
index 25494b9..41c3e6a 100644
--- a/parse_args.c
+++ b/parse_args.c
@@ -91,6 +91,25 @@ static inline int parse_arg_delay(
     return argc;
 }
 
+static inline void print_help_and_exit(const char *argv0) {
+    printf(
+        (
+            "Usage: %s [-h|--help] [--delay DELAY] [--humanize] --pid PID ...\n"
+            "\n"
+            "Options:\n"
+            "-h, --help  display this help\n"
+            "--delay     A timeval (ms) in which to measure\n"
+            "--humanize  Print memory human-readable rather than bytes\n"
+            "--pid PID   Process ids to track. Specify multiple times\n"
+            "            PID+  track all the direct child processes\n"
+            "            PID*  track all child processes recursively\n"
+            "\n"
+        ),
+        argv0
+    );
+    exit(0);
+}
+
 int parse_args(
     int argc,
     char **argv,
@@ -98,6 +117,7 @@ int parse_args(
     struct timeval *delay,
     int *humanize_mem
 ) {
+    const char *argv0 = *argv;
     for (argc--, argv++; argc > 0; argc--, argv++) {
         if (strncmp(*argv, "--pid", 5) == 0)
             argc = parse_arg_pid(argc, &argv, pids);
@@ -105,12 +125,20 @@ int parse_args(
             argc = parse_arg_delay(argc, &argv, delay);
         else if (strcmp(*argv, "--humanize") == 0)
             *humanize_mem = 1;
-        else
+        else if (strcmp(*argv, "--help") == 0 || strcmp(*argv, "-h") == 0) {
+            if (pids->len > 0)
+                free(pids->data);
+            print_help_and_exit(argv0);
+        } else
             argc = -1;
         if (argc == -1) {
             fprintf(stderr, "Error: Could not process argument: '%s'\n", *argv);
             return -1;
         }
     }
+    if (pids->len == 0) {
+        fprintf(stderr, "Error: At least one pid must be passed.\n");
+        return -1;
+    }
     return 0;
 }
diff --git a/perftrace.c b/perftrace.c
index 20eddb7..9a77228 100644
--- a/perftrace.c
+++ b/perftrace.c
@@ -477,7 +477,9 @@ int main(int argc, char *argv[]) {
         setup_signal_handler(SIGALRM, handle_alarm) < 0
         || setup_signal_handler(SIGINT, handle_int) < 0
     )
-        goto error;
+        return EXIT_FAILURE;
+    if (parse_args(argc, argv, &pids, &delay, &humanize_mem) < 0)
+        return EXIT_FAILURE;
     if (
         setitimer(
             ITIMER_REAL, &(struct itimerval){ delay, delay }, NULL
@@ -486,8 +488,6 @@ int main(int argc, char *argv[]) {
         perror("setitimer");
         goto error;
     }
-    if (parse_args(argc, argv, &pids, &delay, &humanize_mem) < 0)
-        return EXIT_FAILURE;
     printf("[\n");
     for (alarm_set = 0; alarm_await(); alarm_set = 0) {
         if (clock_gettime(CLOCK_REALTIME, &current) < 0) {
-- 
2.53.0