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.
Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@xxxxxxxxx>
---
Changelog:
- v2: open code execvp routine into trace-cmd. (Req. Steve Rostedt)
- v1: https://lore.kernel.org/linux-trace-devel/Y7dUo6woh9Y31cdl@xxxxxxxxxxxxxxx/
---
tracecmd/trace-record.c | 59 ++++++++++++++++++++++++++++++++++++-----
1 file changed, 53 insertions(+), 6 deletions(-)
diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 7f0cebe..4a54637 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -1683,6 +1683,58 @@ 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_env;
+ size_t path_len;
+ size_t entry_len;
+ char *ptr_start;
+ char *ptr_end;
+
+ /*
+ * if command specified by user is neither absolute nor
+ * relative than we search for it in $PATH.
+ */
+ if (!strchr(argv[0], '/') && !strchr(argv[0], '.')) {
+ path_env = getenv("PATH");
+ path_len = strlen(path_env);
+ ptr_start = path_env;
+
+ while ((ptr_start - path_env) < path_len) {
+ ptr_end = strchr(ptr_start, ':');
+
+ /* single entry in PATH? */
+ if (!ptr_end)
+ entry_len = path_len;
+ else
+ entry_len = ptr_end - ptr_start;
+
+ strncpy(buf, ptr_start, entry_len);
+
+ if (buf[entry_len - 1] != '/')
+ buf[entry_len++] = '/';
+
+ strncpy(buf + entry_len, argv[0], sizeof(buf) - entry_len);
+
+ /* does it exist and can we execute it? */
+ if (access(buf, X_OK) == 0)
+ break;
+
+ ptr_start = ptr_end + 1;
+ }
+ } else {
+ strncpy(buf, argv[0], sizeof(buf));
+ }
+
+ 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;
@@ -1709,12 +1761,7 @@ 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);
--
2.38.1
|