tracing: expose current->comm to [ku]probe events
ftrace is very quick to give up on saving the task command line (see
`trace_save_cmdline()`). The workaround for events which really care
about the command line is to explicitly assign it as part of the entry.
However, this doesn't work for kprobe events, as there's no
straightforward way to get access to current->comm. Add a kprobe/uprobe
event variable $comm which provides exactly that.
Link: http://lkml.kernel.org/r/f59b472033b943a370f5f48d0af37698f409108f.1465435894.git.osandov@fb.com
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Omar Sandoval <osandov@fb.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 1d372fa..74e80a5 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -218,6 +218,28 @@
kfree(data);
}
+void FETCH_FUNC_NAME(comm, string)(struct pt_regs *regs,
+ void *data, void *dest)
+{
+ int maxlen = get_rloc_len(*(u32 *)dest);
+ u8 *dst = get_rloc_data(dest);
+ long ret;
+
+ if (!maxlen)
+ return;
+
+ ret = strlcpy(dst, current->comm, maxlen);
+ *(u32 *)dest = make_data_rloc(ret, get_rloc_offs(*(u32 *)dest));
+}
+NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string));
+
+void FETCH_FUNC_NAME(comm, string_size)(struct pt_regs *regs,
+ void *data, void *dest)
+{
+ *(u32 *)dest = strlen(current->comm) + 1;
+}
+NOKPROBE_SYMBOL(FETCH_FUNC_NAME(comm, string_size));
+
static const struct fetch_type *find_fetch_type(const char *type,
const struct fetch_type *ftbl)
{
@@ -348,6 +370,11 @@
}
} else
ret = -EINVAL;
+ } else if (strcmp(arg, "comm") == 0) {
+ if (strcmp(t->name, "string") != 0 &&
+ strcmp(t->name, "string_size") != 0)
+ return -EINVAL;
+ f->fn = t->fetch[FETCH_MTD_comm];
} else
ret = -EINVAL;
@@ -522,6 +549,12 @@
arg[t - parg->comm] = '\0';
t++;
}
+ /*
+ * The default type of $comm should be "string", and it can't be
+ * dereferenced.
+ */
+ if (!t && strcmp(arg, "$comm") == 0)
+ t = "string";
parg->type = find_fetch_type(t, ftbl);
if (!parg->type) {
pr_info("Unsupported type: %s\n", t);