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:
- v4: handle case in which path is relative but not './' is used.
(Req. Steven Rostedt)
- v3: simplify path traversal code via strtok_r. (Req. Steven Rostedt)
- v2: open code execvp routine into trace-cmd. (Req. Steven Rostedt)
- v1: https://lore.kernel.org/linux-trace-devel/Y7dUo6woh9Y31cdl@xxxxxxxxxxxxxxx/
Tests made (that's should help during the review):
# Path-dependent
./tracecmd/trace-cmd <args> -F ls
# relative path with '.'
./tracecmd/trace-cmd <args> -F ../../../../usr/bin/ls
# absolute path
./tracecmd/trace-cmd <args> -F /usr/bin/ls
# relative path with no dots
mkdir test_bin && cp /usr/bin/ls test_bin/ \
&& ./tracecmd/trace-cmd <args> -F test_bin/ls \
&& rm -rf test_bin
---
tracecmd/trace-record.c | 48 +++++++++++++++++++++++++++++++++++------
1 file changed, 41 insertions(+), 7 deletions(-)
diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 7f0cebe..32fbfef 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);
--
2.38.1
|