diff options
author | Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com> | 2023-01-22 14:44:44 +1300 |
---|---|---|
committer | Steven Rostedt (Google) <rostedt@goodmis.org> | 2023-02-02 10:40:09 -0500 |
commit | edf9424029cc4a05166100a5957fab6a13791880 (patch) | |
tree | 410a8a84a999d895f827fb0ca6e28f2e58ce9273 | |
parent | 0a68daed9f58e4429c0f1e7818f7cc0634873112 (diff) | |
download | trace-cmd-edf9424029cc4a05166100a5957fab6a13791880.tar.gz |
trace-cmd: Open code execvp routine to avoid multiple execve syscalls
In tracecmd/trace-record.c:<run_cmd>, trace-cmd record -F <executable>
is launched via the libc's execvp() routine. The way that execvp() routine
works is by invoking execve syscall for every entry on the $PATH if
command specified is neither absolute nor relative which can come across
as a bit cryptic to untrained eyes.
- absolute path example:
# trace-cmd record -p function_graph \
-g __x64_sys_execve -O nofuncgraph-irqs \
-n __cond_resched --max-graph-depth 1 \
-F /usr/bin/echo "ftrace" > /dev/null
# trace-cmd report
echo-172994 [000] 185539.798539: funcgraph_entry: ! 803.376 us | __x64_sys_execve();
- PATH-dependent path example:
# trace-cmd record -p function_graph \
-g __x64_sys_execve -O nofuncgraph-irqs \
-n __cond_resched --max-graph-depth 1 \
-F echo "ftrace" > /dev/null
# trace-cmd report
echo-172656 [002] 185009.671586: funcgraph_entry: ! 288.732 us | __x64_sys_execve();
echo-172656 [002] 185009.671879: funcgraph_entry: ! 158.337 us | __x64_sys_execve();
echo-172656 [002] 185009.672042: funcgraph_entry: ! 161.843 us | __x64_sys_execve();
echo-172656 [002] 185009.672207: funcgraph_entry: ! 157.656 us | __x64_sys_execve();
echo-172656 [002] 185009.672369: funcgraph_entry: ! 156.343 us | __x64_sys_execve();
echo-172656 [002] 185009.672529: funcgraph_entry: ! 863.629 us | __x64_sys_execve();
Open code the libc's execvp routine into trace-cmd so ftrace will only
start recording once the command is found when it needs to be found in
PATH.
Link: https://lore.kernel.org/linux-trace-devel/Y8yVDI93geYhLQio@mail.google.com
Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
-rw-r--r-- | tracecmd/trace-record.c | 48 |
1 files changed, 41 insertions, 7 deletions
diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c index 7f0cebe8..32fbfef5 100644 --- a/tracecmd/trace-record.c +++ b/tracecmd/trace-record.c @@ -1683,6 +1683,46 @@ static int change_user(const char *user) return 0; } +static void execute_program(int argc, char **argv) +{ + char buf[PATH_MAX + NAME_MAX + 1]; + char *path; + char *entry; + char *saveptr; + + /* + * if command specified by user is neither absolute nor + * relative than we search for it in $PATH. + */ + if (!strchr(argv[0], '/')) { + path = getenv("PATH"); + + if (!path) + die("can't search for '%s' if $PATH is NULL", argv[0]); + + for (entry = strtok_r(path, ":", &saveptr); + entry; entry = strtok_r(NULL, ":", &saveptr)) { + + snprintf(buf, sizeof(buf), "%s/%s", entry, argv[0]); + + /* does it exist and can we execute it? */ + if (access(buf, X_OK) == 0) + break; + + } + } else { + strncpy(buf, argv[0], sizeof(buf)); + } + + tracecmd_enable_tracing(); + if (execve(buf, argv, environ)) { + fprintf(stderr, "\n********************\n"); + fprintf(stderr, " Unable to exec %s\n", argv[0]); + fprintf(stderr, "********************\n"); + die("Failed to exec %s", argv[0]); + } +} + static void run_cmd(enum trace_type type, const char *user, int argc, char **argv) { int status; @@ -1693,7 +1733,6 @@ static void run_cmd(enum trace_type type, const char *user, int argc, char **arg if (!pid) { /* child */ update_task_filter(); - tracecmd_enable_tracing(); if (!fork_process) enable_ptrace(); /* @@ -1709,12 +1748,7 @@ static void run_cmd(enum trace_type type, const char *user, int argc, char **arg if (change_user(user) < 0) die("Failed to change user to %s", user); - if (execvp(argv[0], argv)) { - fprintf(stderr, "\n********************\n"); - fprintf(stderr, " Unable to exec %s\n", argv[0]); - fprintf(stderr, "********************\n"); - die("Failed to exec %s", argv[0]); - } + execute_program(argc, argv); } if (fork_process) exit(0); |